*Article* **Differences in Femoral Artery Occlusion Pressure between Sexes and Dominant and Non-Dominant Legs**

**Nicole D. Tafuna'i 1 , Iain Hunter 1 , Aaron W. Johnson 1 , Gilbert W. Fellingham <sup>2</sup> and Pat R. Vehrs 1, \***


**Abstract:** *Background and Objectives*: Blood flow restriction during low-load exercise stimulates similar muscle adaptations to those normally observed with higher loads. Differences in the arterial occlusion pressure (AOP) between limbs and between sexes are unclear. We compared the AOP of the superficial femoral artery in the dominant and non-dominant legs, and the relationship between blood flow and occlusion pressure in 35 (16 males, 19 females) young adults. *Materials and Methods*: Using ultrasound, we measured the AOP of the superficial femoral artery in both legs. Blood flow at occlusion pressures ranging from 0% to 100% of the AOP was measured in the dominant leg. *Results*: There was a significant difference in the AOP between males and females in the dominant (230 ± 41 vs. 191 ± 27 mmHg; *p* = 0.002) and non-dominant (209 ± 37 vs. 178 ± 21 mmHg; *p* = 0.004) legs, and between the dominant and non-dominant legs in males (230 ± 41 vs. 209 ± 37 mmHg; *p* = 0.009) but not females (191 ± 27 vs. 178 ± 21 mmHg; *p* = 0.053), respectively. Leg circumference was the most influential independent predictor of the AOP. There was a linear relationship between blood flow (expressed as a percentage of unoccluded blood flow) and occlusion pressure (expressed as a percentage of AOP). *Conclusions*: Arterial occlusion pressure is not always greater in the dominant leg or the larger leg. Practitioners should measure AOP in both limbs to determine if occlusion pressures used during exercise should be limb specific. Occlusion pressures used during blood flow restriction exercise should be chosen carefully.

**Keywords:** resistance exercise; blood flow restriction; blood flow restriction exercise

#### **1. Introduction**

Blood flow restriction (BFR) applied to the arms or legs during low-load resistance training is effective in promoting hypertrophy and increasing or maintaining muscle strength [1–5]. Blood flow restriction exercise (BFRE) can be part of musculoskeletal rehabilitation following an injury or surgery or for those trying to counter muscle wasting due to chronic disease [4,6,7]. The muscular adaptations to BFRE contribute to the popularity of this method of resistance training among athletes and in the fitness industry.

Blood flow restriction partially restricts arterial blood flow into the limb and occludes venous blood flow out of the muscle [6–9]. Some studies [10,11] used elastic wraps as a "practical" method of BFR, but this could produce inconsistent blood flow restriction between two limbs and between exercise sessions. Most studies have restricted blood flow with an inflatable cuff. Early studies used absolute cuff pressures [7,8,12–16] ranging from 50 to 300 mmHg, but this is problematic in that a given cuff pressure represents a different level of occlusion and blood flow restriction for each person. The current recommendation [5,17] is to use a percentage of the arterial occlusion pressure (AOP) to restrict blood flow during BFRE. Although further research is needed to determine the optimal pressure to use during BFRE, it appears that a pressure equivalent to 50% to 80% of the AOP is appropriate during low-load resistance training [5].

**Citation:** Tafuna'i, N.D.; Hunter, I.; Johnson, A.W.; Fellingham, G.W.; Vehrs, P.R. Differences in Femoral Artery Occlusion Pressure between Sexes and Dominant and Non-Dominant Legs. *Medicina* **2021**, *57*, 863. https://doi.org/10.3390/ medicina57090863

Academic Editor: Filipe Manuel Clemente

Received: 23 July 2021 Accepted: 21 August 2021 Published: 24 August 2021

**Publisher's Note:** MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

**Copyright:** © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

Although a plethora of papers have been published on the topic of BFR and BFRE, some things remain unclear, including the relationship between blood flow and occlusion pressure, sex differences in AOP, and differences in AOP between dominant and nondominant limbs. Differences in the AOP between individuals is attributed primarily to differences in limb circumference [5,18]. To date, studies have not reported the AOP in the dominant and non-dominant limbs in an individual. In most of the literature where occlusion pressure is based on a percentage of AOP, dominance of the occluded limb is not reported in unilateral interventions and any differences between limbs are not reported in bilateral studies [19–24]. Any differences in AOP between the dominant and non-dominant limbs may be due to differences in limb circumference. Although previous studies have included male and female participants, sex differences in AOP have not been reported. After accounting for potential differences in limb circumference, little evidence suggests that there is a sex difference in AOP. Some authors have reported that the relationship between arterial blood flow and absolute cuff pressure in the leg is linear [7,8,12,25] but a recent study [26] reported a nonlinear relationship between relative arterial blood flow and cuff pressures with a plateau in blood flow at pressures between 40–80% AOP.

The purposes of this study were to compare the AOP of the superficial femoral artery (SFA) in the dominant and non-dominant legs, and blood flow at relative occlusion pressures (0–100% AOP) in the dominant leg at rest in young healthy men and women. We hypothesized a direct positive relationship between limb circumference and AOP, no significant difference in AOP between the sexes or between the dominant and nondominant legs, and no significant sex difference in the relationship between arterial blood flow and relative occlusion pressure.

#### **2. Materials and Methods**

This study was a cross-sectional study that measured the AOP in the SFA of both legs and blood flow in the dominant leg at cuff pressures representing 0%, 20%, 40%, 60%, 80%, and 100% of the AOP. The primary variables of interest included the AOP (mmHg) and blood flow at each increment of blood flow restriction (% AOP). This study was reviewed and approved by the Institutional Review Board for the use of Human Subjects prior to the collection of any data.

#### *2.1. Participants*

A total of 35 (16 males, 19 females) physically active and apparently healthy adults, 18–35 years of age participated in this study. Interested participants were excluded from participation if they had any known risk factors for cardiovascular disease or one or more risk factors for thromboembolism, which include: obesity (BMI ≥ 30 kg/m<sup>2</sup> ), diagnosed Crohn's disease, a previous fracture of the hip, pelvis, or femur, a major surgery in the last 6 months, varicose veins, a family history of deep vein thrombosis or pulmonary embolism, and on oral birth control [22,27–29]. Individuals were also excluded if a) they had been diagnosed as having or were being treated for cardiovascular disease, renal disease, diabetes, or hypertension, b) their resting systolic blood pressure (SBP) ≥ 130 or diastolic blood pressure (DBP) ≥ 80 mmHg, or c) they were pregnant or less than 6 months postpartum. To minimize the effects of hormone variability later in the menstrual cycle, females participated in the study within the first 14 days of their menstrual cycle.

#### *2.2. Procedures*

Subjects were instructed to refrain from eating during the 2 h prior to their participation, consuming caffeine for the previous 8 h, and participating in vigorous physical activity the previous 24 h [28,29]. All procedures for each subject were completed in one visit to the lab. The methods, expectations, risks, and benefits of the study were explained to each subject after which they voluntarily provided written informed consent.

The subject's height (cm) was measured using a calibrated wall-mounted stadiometer scale (SECA Model 264; SECA, Cino, CA, USA). Body mass (kg) was measured using a

digital scale (Ohaus Model CD-33, Ohaus Corporation, Pine Brook, NJ, USA) and BMI (kg/m<sup>2</sup> ) was calculated from measured height and body mass values. Subjects then sat quietly in a comfortable chair for 5 min with legs uncrossed. Blood pressure was measured on the right arm and the average of two blood pressure measurements was recorded, or if they were not within 5 mmHg of each other, blood pressure was measured a third time, and the two closest measurements were averaged. Mean arterial pressure (MAP) was calculated as DBP plus one-third of pulse pressure. Leg dominance was determined by self-report by asking "I you were to kick a ball, with which leg would you use to kick the ball? [30]. The circumference and skinfold thickness of the dominant and non-dominant thighs were measured in triplicate in the standing position using a spring-loaded Gullick measuring tape and a calibrated Lange caliper (Santa Cruz, CA, USA), respectively. Measurements were taken at one-third of the distance between the inguinal crease and the top of the patella. The average of the three measurements was used in the data analysis.

#### *2.3. Blood Flow Measurements*

All blood flow measurements were performed using a handheld Doppler probe (9 MHz; 55 mm) and GE ultrasound machine with an integrated ECG (GE LOGIQ, GE Healthcare). Blood flow restriction was accomplished using a Hokanson SC10 cuff (10 cm wide; 85 cm long) attached to an E-20 rapid cuff inflator (Hokanson, Bellevue, WA, USA). The occlusion cuff was placed on the participant's thigh one-third of the distance between the inguinal fold and the top of the patella and blood flow in the SFA was measured distal to the cuff. Color flow mode and pulse wave forms were viewed to determine the presence of blood flow. During the entire time of testing, participants were in a semi-reclined (15◦ ) position to allow reasonable access to the SFA using the ultrasound. Angle of insonation of the ultrasound probe was maintained at 60◦ .

#### *2.4. Measurement of Arterial Occlusion Pressure*

The AOP of the SFA in the dominant and non-dominant legs was measured once in a randomized order for each participant. A hand-held Doppler probe was used to detect a pulse wave in the SFA distal to the cuff with the cuff deflated. The cuff was then inflated to 50 mmHg and then gradually increased until arterial flow and pulse waves were no longer detected. After the AOP was recorded, the cuff was deflated, removed, and placed on the other leg. The participant rested for 5 min [20,27,29] with the cuff deflated, after which the process was repeated.

#### *2.5. Measurement of Arterial Blood Flow*

Following at least 5 min after the second AOP measurement, we measured arterial blood flow for 1 min at cuff pressures equivalent to 0%, 20%, 40%, 60%, 80%, and 100% of the subject's previously measured AOP in a randomized order. There was a 5 min rest period between measurements with the cuff deflated. One-minute video clips were stored for later analysis. Using the integrated ECG and pulse waves as reference points, femoral artery diameter was measured at two time periods representing the end of diastole (just before the QRS) and during systole (at the peak of the QRS) of each cardiac cycle. The two measurements were averaged for each beat over five 12-s periods. Time averaged blood flow velocity (TAV) over the five 12-s periods was recorded. Blood flow (mL/min) was calculated automatically by the ultrasound machine as follows:

Blood flow (mL/min) = Cross sectional area (cm<sup>2</sup> ) × TAV (cm/s) × 60 s/min

#### *2.6. Data Analysis*

Sex differences in age, height, body mass, BMI, blood pressure measurements (i.e., SBP, DBP, MAP), leg circumference, thigh skinfold thickness, and AOP in the dominant and nondominant legs were determined using two-sample *t*-tests. Differences in leg circumference, thigh skinfold thickness, and AOP between the dominant and non-dominant legs in males and females were determined using paired *t*-tests. The influence of sex, SBP, DBP, MAP, thigh skinfold and circumference measurements on the AOP was evaluated using regression analysis.

Analysis of arterial blood flow data, expressed as a percentage of unoccluded blood flow, and occlusion pressure, expressed as a percentage of individual AOP (0%, 20%, 40%, 60%, 80%, 100%) presented two major challenges. The first was that relative blood flow when there was no occlusion (0% AOP) is represented as 100% for every subject and there is no variance in the data. Second, blood flow at various degrees of occlusion (e.g., 20%, 40%, 60% AOP) for some subjects was higher than when there was no occlusion (0% AOP). Thus, the difficulty in analyzing the blood flow data was that there was one data point (0% AOP) where there is no variance in blood flow (blood flow = 100%) and other data points where relative blood flow was greater than that measured at 0% AOP (blood flow = 100%). To analyze these data, we first used a one-sample *t*-test to determine if relative blood flow at 20% AOP was significantly different from relative blood flow at 0% AOP. We found that the average relative blood flow at 20% AOP was 81% (CI = 70.4−91.6%) of unoccluded blood flow (*p* = 0.0009). Since each subject had multiple data points, we then fit a mixed linear model between relative blood flow and relative occlusion pressure to account for within- and between-subject variability. To further appropriately account for variability when fitting the model, we omitted the blood flow data at 0% AOP and only used data at occlusion pressures of 20%, 40%, 60%, 80%, and 100% of AOP. The initial analysis revealed that there was no sex difference in the relationship between blood flow and occlusion pressure. We therefore fit a linear model that did not include sex as a variable. A 95% confidence interval (CI) and prediction interval (PI) were computed for the line of best fit through the data.

#### **3. Results**

Participant characteristics are shown in Table 1. Males were taller, heavier and had higher SBP and MAP than their female counterparts. There were no significant differences in the circumferences of the dominant and non-dominant legs in males (*p* = 0.1897) or in females (*p* = 0.0895) or of the dominant (*p* = 0.847) or non-dominant legs (*p* = 0.746) between males and females. There were no significant differences in the thigh skinfold between the dominant and non-dominant legs of either males (*p* = 0.7630) or females (*p* = 0.5923) or of the dominant leg (*p* = 0.056) and non-dominant leg (*p* = 0.054) between males and females.

**Table 1.** Participant Characteristics.




Values are mean ± SD. BMI = body mass index, SBP = systolic blood pressure, DBP = diastolic blood pressure, MAP = mean arterial pressure. \* = significant difference between males and females (*p* < 0.05); ˆ = significant difference between dominant and non-dominant leg (*p* < 0.05).

#### *3.1. Arterial Occlusion Pressure*

There was a significant difference in the AOP between males and females in the dominant (230 ± 41 vs. 191 ± 27 mmHg; *p* = 0.002) and non-dominant (209 ± 37 vs. 178 ± 21 mmHg; *p* = 0.004) legs, respectively. There was a significant difference in the AOP between the dominant and non-dominant legs in males (230 ± 41 vs. 209 ± 37 mmHg; *p* = 0.009) but not in females (191 ± 27 vs. 178 ± 21 mmHg; *p* = 0.053). Regression analysis revealed that after leg circumference entered the equation, SBP, DBP, MAP, skinfold thickness, age, and sex were not significant independent predictors of AOP. The resulting regression model as shown in Figure 1 with 95% CI and 95% PI was:

#### AOP (mmHg) = 40.4 + (3.23) Leg Circumference (cm)

**Figure 1.** Relationship between limb circumference and arterial occlusion pressure. Solid line = line of best fit. Dashed lines = 95% Prediction Intervals. Dotted lines = 95% Confidence Intervals.

#### *3.2. Arterial Blood Flow*

− The mixed model analysis revealed a linear relationship between relative blood flow (% unoccluded blood flow) and relative occlusion pressure (%AOP). The resulting equation (R = −0.842; Residual Standard Error = 25.3) as shown in Figure 2 with 95% CI and 95% PI was:

Percent Blood Flow = 99.46 − 0.85 (Occlusion Pressure; %AOP)

−

**Figure 2.** Relationship between arterial blood flow and occlusion pressure. Solid line = line of best fit. Dashed lines = 95% Prediction Intervals. Dotted lines = 95% Confidence Intervals.

#### **4. Discussion**

This paper adds to the current body of knowledge about BFR in that we report, perhaps for the first time, large differences in AOP between males and females and between the dominant and non-dominant legs. The linear relationship between blood flow and occlusion pressure expressed in relative terms was unrelated to sex. We also report a large variance in blood flow data at different levels of occlusion that is not unique to this study but has not been previously discussed. The findings of this study have implications for future research and those using BFRE.

#### *4.1. Sex and Limb Differences in Arterial Occlusion Pressure*

We report a large sex difference in AOP in both the dominant and non-dominant legs (Table 1). Although other studies have included male and female participants, sex differences in AOP have not been reported [21,26,31,32]. To the best of our knowledge, only one previous study has reported a sex difference in AOP. Jessee et al. [27] reported that the AOP of the right arm of females was on the average 4–7 mmHg (*p* < 0.05) lower than in males across three different cuff sizes. Although significantly different, the authors suggest that the differences in AOP were inconsequential in prescribing BFRE.

It is well reported that differences in the AOP can be attributed primarily to differences in limb circumference [7,18,33]. The larger the limb, the greater the pressure required to occlude the blood vessel. Larger limbs have more mass between the skin and the blood vessels that must be compressed to occlude the vessel, and higher pressures are required to transmit adequate force to the deeper tissues [20,21]. Hence, it follows that sex differences in AOP or differences in AOP between limbs may be accounted for by differences in limb circumference. Jessee et al. [27] reported an average sex difference in circumference of the right arm of 5.3 cm and that after accounting for arm circumference, arm length, SBP, and DBP, sex remained a significant independent predictor of AOP. In this study, there was an average difference in circumference of <1 cm in both the dominant and non-dominant legs between and within males and females (Table 1). Despite a small average difference in leg circumference, there was a large difference in AOP between the dominant and nondominant legs within and between males and females (Table 1). This could be attributed to the fact that the difference in the circumferences of the dominant and non-dominant leg

ranged from the dominant leg being 5.5 cm smaller to 7 cm larger than the non-dominant leg in males and 2.5 cm smaller to 3.5 cm larger in females. The regression analysis in this study indicates that after accounting for leg circumference, SBP, DBP, MAP, skinfold thickness, sex, and age were not significant predictors of AOP. The differences in the results between this study and that of Jessee et al. [27] might be explained by the differences in the size of the limbs studied (i.e., legs vs. arms). In addition, we report the AOP of both the dominant and non-dominant legs, whereas Jessee et al. only reported the AOP of the right arm, rather than the dominant arm. It should be appreciated that the leg circumference of the dominant leg is not always larger than that of the non-dominant leg. In this study, the dominant leg was larger than the non-dominant leg in 20 of the participants (8 males, 12 females) and the non-dominant leg was larger in 15 of the participants (8 males, 7 females). Likewise, the AOP is not always higher in the larger leg. In this study, the AOP was higher in the larger leg of 21 participants (15 dominant, 6 non-dominant; 9 males, 12 females) and higher in the smaller leg of 14 participants (9 dominant, 5 non-dominant; 7 males, 7 females).

Considering that the overall average difference in AOP between the dominant and non-dominant legs in this study was 17 mmHg (Table 1), an occlusion pressure of 50% of AOP would result in a difference in occlusion pressure of less than 9 mmHg between legs. This small difference in occlusion pressure between the two limbs would be of little import during BFRE. Nevertheless, the greatest difference in AOP between the two legs in an individual in this study was 80 mmHg. In this subject, the difference in occlusion pressure between the two legs during BFRE would be of practical significance. Our data suggest that AOP should be measured in both legs to determine if a sufficient difference existed that would justify using occlusion pressures specific to each leg. Most practitioners (e.g., physical therapists, personal trainers, strength and conditioning coaches, etc.) are unable to measure AOP in their clients or patients. Nevertheless, health and fitness professionals should be aware of differences between limbs that could affect the safe use of BFR during exercise. End-users should not be naïve of the potential differences between limbs and should use BFR during exercise with appropriate caution. Although further research is needed, occlusion pressures at a perceived pressure [10,11] could account for difference between limbs when measures of occlusion pressure are not possible.

The composition of the limb may also influence the pressure required to occlude a blood vessel. In this study, the sex differences in thigh skinfold thickness approached the alpha-level of 0.05 but likely did not enter into the regression equation to estimate AOP because it is included as part of the overall circumference of the leg and represents only a portion of the total tissue mass that must be compressed to occlude the femoral artery. Our data concur with that of Loenneke et al. [21] who, after using B-mode ultrasound to measure fat thickness of the upper arm of 171 males and females, concluded that the absolute size of the arm may be more important than the composition of the arm in predicting AOP.

#### *4.2. Arterial Blood Flow*

Since blood flow at any given absolute pressure varies widely between individuals, it is appropriate to express blood flow and occlusion pressure in relative terms. The results of this study (Figure 2) indicate a linear relationship between blood flow (% unoccluded blood flow) and relative occlusion pressure (%AOP). Our data concur with those of a previous study reporting a linear relationship between relative blood flow and %AOP in the posterior tibial artery [25]. This is contrary to recently reported nonlinear relationships between relative blood flow and relative occlusion pressure and plateaus in blood flow between 40% to 80% AOP in the brachial artery [34,35] and the SFA [26]. Some difference in methodology between studies could help explain the disparity in the results. For example, subjects in our study were in a semi reclined position, whereas subjects in Crossley et al. [26] study were in the seated position. Additionally, measurements in the study by Crossley et al. were performed on alternating legs in a randomized order over the course of the

study so the reported AOP and blood flow represented AOP and blood flow in both legs rather than either the dominant or non-dominant leg.

Whether the relationship between blood flow and occlusion is linear or nonlinear is of practical importance. A nonlinear relationship suggests that use of a lower, more comfortable and potentially safer occlusion pressure (e.g., 40% AOP) would provide an equally effective stimulus during BFRE as higher occlusion pressures. A linear relationship suggests that the occlusion pressure used during BFRE should be selected more carefully and that further research is required to determine a recommended reduction in blood flow to be used during BFRE.

#### *4.3. Variance in Blood Flow Measurements*

In this study, we observed a large variation in blood flow at different levels of occlusion. For example, we note that blood flow at higher levels of occlusion was sometimes greater than at lower levels of occlusion. We also found that some participants had notable blood flow at an occlusion pressure equivalent to the previously measured AOP. Variance in the data presented in this study is apparent in the wide prediction intervals shown in Figure 2. These observations are suggestive of a robust cardiovascular system that maintains blood flow across various levels of occlusion pressures [35].

Evidence of the variation in blood flow measurements is present in previous studies. For example, close examination of previously reported blood flow data [34] reveals that relative blood flow at 70% AOP was greater than relative blood flow at 60% and 50% AOP. Likewise, previously reported large standard deviations of blood flow data [35] suggest that in some subjects, blood flow at higher occlusion pressures was greater than at lower occlusion pressures. This could be attributed to a cardiovascular response to high occlusion pressures in the absence of exercise [7,36]. It could also be possible that after several applications of BFR there are local responses in the vasculature that alters blood flow or the AOP. Although previous research indicates that blood flow returns to normal within 30 to 90 s after the occlusion is removed [37], longer rest periods may be needed between sequential blood flow measurements with occlusion. It is possible that after multiple occlusions of blood flow, the AOP changes. This could influence the expression of blood flow relative to AOP. Lastly, although data collected from each subject in this study occurred in a single day, Mouser et al. [35] reported a significant day-to-day variation in resting blood flow that clearly has implications for future research involving blood flow measurements over multiple days and the use of BFRE. Our data and close examination of data presented in the literature warrants a call for further studies evaluating the variance and reliability of blood flow measurements during BFR.

#### *4.4. Study Limitations*

This study had several limitations. Participants were college-age coeds without known risk factors for cardiometabolic diseases. Therefore, the results of our study may not be applicable to all populations. Blood pressure was not measured during the measurement of blood flow at different occlusion pressures. Having blood pressure measurements could lead to a better understanding of the relationship between occlusion pressure and blood flow. Blood pressure measurements during blood flow occlusion may also help explain the variation in blood flow at different occlusion pressures. In this study, the Hokanson SC10 cuff (10 cm wide; 85 cm long) attached to an E-20 rapid cuff inflator (Hokanson, Bellevue, WA, USA) was used for all measurements. Clinicians, researchers, and other practitioners may use different brands of cuffs and inflation systems, different cuff sizes, or other methods to occlude blood flow. Lastly, a greater number of subjects could improve the data when comparing limb and sex differences in AOP.

#### *4.5. Direction for Future Studies*

Based on the results of this study, future studies should include both male and female participants and report limb dominance, AOP, and blood flow data on both limbs in males and females. Limb circumference or other measures of limb volume should also be reported. While it is clear that limb circumference is more influential on AOP than limb composition, the sex differences in thigh skinfold thickness reported in this study and the influence of fat thickness reported by Loenneke et al. [21] lend support for an influence of limb composition on AOP that needs further investigation. The large variation of blood flow measurements at different occlusion pressures reported in this and previous studies suggests the need to standardize blood flow measurement methods and investigate the reliability of AOP and blood flow measurements. Comparing blood flow and variability in blood flow at different occlusion pressures between the dominant and non-dominant leg is also warranted. Measuring blood pressure during occlusion may help explain variation in blood flow at different occlusion pressures. Assessments of reliability in measurements of blood flow with and without occlusion between test administrators, within and between days needs attention.

#### **5. Conclusions**

An important finding of this study was large sex differences in AOP in both the dominant and non-dominant legs and large differences in AOP between the dominant and non-dominant legs particularly in men. Arterial occlusion pressure is not always greater in the dominant leg or the larger leg. Practitioners should measure AOP in both limbs to determine if occlusion pressures used during exercise should be limb specific. We also report a linear relationship between relative occlusion pressure and blood flow. The large variance in blood flow at different occlusion pressured warrants further study and caution during BFRE. These findings are of practical importance when using BFRE in various settings and suggest the need for continued research. Occlusion pressures used during blood flow restriction exercise should be chosen carefully.

**Author Contributions:** Conceptualization, N.D.T., I.H., P.R.V. and A.W.J.; methodology, N.D.T., A.W.J., G.W.F. and P.R.V.; formal analysis, N.D.T., A.W.J., G.W.F., P.R.V.; investigation, N.D.T., A.W.J. and P.R.V.; resources, P.R.V. and A.W.J.; writing—original draft preparation, N.D.T. and P.R.V.; writing—review and editing, I.H., A.W.J. and G.W.F.; project administration, N.D.T. and P.R.V. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Institutional Review Board Statement:** The study was conducted according to the guidelines of the Declaration of Helsinki and approved by the Institutional Review Board of Brigham Young University (Protocol X19019; 5 March 2019).

**Informed Consent Statement:** Informed written consent was obtained from all subjects involved in the study.

**Data Availability Statement:** The data presented in this study are available upon request from the corresponding author. The data are not publicly available.

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **References**


## *Article* **Anabolic–Androgenic Steroid Abuse among Gym Users, Eastern Province, Saudi Arabia**

**Walied Albaker 1 , Ali Alkhars 1 , Yasir Elamin 1 , Noor Jatoi 1 , Dhuha Boumarah <sup>1</sup> and Mohammed Al-Hariri 2, \***


**Abstract:** *Background and Objectives*: The main aim of the present study was to assess the use of androgenic–anabolic steroids (AAS) and to investigate its potentially unfavorable effects among gym members attending gym fitness facilities in Eastern Province, Saudi Arabia. *Materials and Methods*: A cross-sectional questionnaire-based study was carried out during the summer of 2017. Male gym users in the Eastern Province region of Saudi Arabia were the respondents. Information on socio-demographics, use of AAS, knowledge, and awareness about its side effects were collected using a self-administered questionnaire. *Results:* The prevalence of AAS consumption among trainees in Eastern Province was 21.3%. The percentage was highest among those 26–30 years of age (31.9%), followed by the 21–25 (27.4%) (*p* = 0.003) age group. Participants in the study were not aware of the potential adverse effects of AAS use. Adverse effects experienced by 77% of AAS users include psychiatric problems (47%), acne (32.7%), hair loss (14.2%), and sexual dysfunction (10.7%). Moreover, it appears that trainers and friends are major sources (75.20%) for obtaining AAS. *Conclusion:* AAS abuse is a real problem among gym members, along with a lack of knowledge regarding its adverse effects. Health education and awareness programs are needed not only for trainees, but also for trainers and gym owners as they are reportedly some of the primary sources of AAS.

**Keywords:** anabolic steroids; gym members; male; gym; abuse

#### **1. Introduction**

Androgenic–anabolic steroids (AAS) are synthetically occurring products of the male sex hormone (Testosterone) [1]. They have two major effects which are anabolic and androgenic in nature [2]. The anabolic effect leads to decreased body fat and increases bone density and skeletal muscle mass, as well as stimulating erythropoiesis [3]. The androgenic effects are associated with the development of male sexual characteristics [4]. They have a significant effect on athletic performance [1].

A higher level of AAS in the body can lead to several psychological and physical complications. Examples of the physical problems that AAS can lead to are high blood pressure, atherosclerosis, myocardial infarction, cardiac hypertrophy, fluid retention, jaundice, acne, and hepatic tumors [1,5]. Psychiatric problems such as aggressiveness, euphoria, irritability, and mood disturbance can occur. Furthermore, AAS can indeed cause reduced sperm count, shrinking of the testicles, infertility, baldness, and the development of prostate and breast cancers [6].

Most countries permit the use of AAS to treat medical conditions by prescription [7]. Studies show an increasing rate of AAS use among athletes worldwide. However, the World Anti-Doping Agency lists AAS as prohibited substances [8].

**Citation:** Albaker, W.; Alkhars, A.; Elamin, Y.; Jatoi, N.; Boumarah, D.; Al-Hariri, M. Anabolic–Androgenic Steroid Abuse among Gym Users, Eastern Province, Saudi Arabia. *Medicina* **2021**, *57*, 703. https:// doi.org/10.3390/medicina57070703

Academic Editors: Filipe Manuel Clemente and Jose Antonio de Paz

Received: 2 June 2021 Accepted: 7 July 2021 Published: 10 July 2021

**Publisher's Note:** MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

**Copyright:** © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

Many bodybuilders turn to these medications to increase muscle size, strength, and overall efficiency with less effort over a shorter time rather than relying on physical exercise and a healthy diet alone [9].

Data show that AAS abuse is more prevalent in Brazil, Western countries, and the Middle East, and is less prevalent in Asia and Africa [10]. A few studies have evaluated the prevalence and awareness about the use of AAS among bodybuilders in Saudi Arabia. Previously reported data found that AAS ranked the highest among Saudi athletes who tested positive for prohibited agents [5]. Another study evaluating AAS abuse among bodybuilders in the southern province of Saudi Arabia (Jazan) revealed a lifetime prevalence of 31% [11].

The prevalence of AAS abuse was lower in the 316 male gym users in the northwestern region of Saudi Arabia (11.4%) [12]. Meanwhile, many studies have concluded that a lack of knowledge is the most likely cause regarding the use of AAS and its adverse effects on Saudi gym members. These studies also recommended a national awareness program in the central (Riyadh) [5], western (Jeddah) [12], and southern (Jazan) [11] regions of Saudi Arabia. Therefore, the present study sought to assess the prevalence of androgenic–anabolic steroid (AAS) use, and to investigate motivations for use and knowledge of its potentially unfavorable effects among gym center visitors in Eastern Province, Saudi Arabia.

#### **2. Materials and Methods**

A cross-sectional survey-based study was conducted on participants visiting gymnasiums in the Eastern Province (Al-Hufof, Ad-Dammam, Al-Khobar, Al-Qatif, Al-Jubail, and Saihat), Kingdom of Saudi Arabia, during the summer of 2017.

The calculation of the sample size was based on a prevalence of AAS of 50%, with a 95% confidence interval (CI). The inclusion criteria were the following: male, older than 18 years, and willingness to take part. We excluded repeated registration in multiple centers or incomplete responses.

The Ethics Committee of Imam Abdulrahman Bin Faisal University approved the research proposal and questionnaire (IRB-2018-01-174, approval date, 27 September 2018). All the participants agreed to participate and signed a consent form before entering into the study.

#### *2.1. Questionnaire*

A self-administered questionnaire was used for data collection. The questionnaire was designed based on previous similar studies reported in the literature on the same topic [12,13]. A pilot study was then carried out to determine the reliability and validity of the questionnaire. The feedback was analyzed and a finalized questionnaire was created accordingly. The final version of the questionnaire consisted of questions on (1) sociodemographic characteristics; (2) overall knowledge about the most commonly used and adverse effects of anabolic steroids; (3) prevalence of side effects experienced by users; and (4) the practices and patterns of AAS use. A single set of questionnaires was distributed (Arabic version).

#### *2.2. Statistical Analysis*

The statistical analysis was performed using SPSS software version 23.0 (SPSS Inc., Chicago, IL, USA). Descriptive statistics were used to explain the categorical and outcome items. A comparison between subgroups was made using Pearson's Chi-square test. A *p*-value less than 0.05 was used to indicate statistical significance.

#### **3. Results**

#### *3.1. Sociodemographic Characteristics*

Nearly 597 eligible gym members were invited to participate in the present study. A total of 541 participants answered the questionnaire and were included in the study according to the calculated sample size, with an overall response rate of 90.6%. Table 1 shows

the characteristics of the study sample. Most of the users (67.1%) belong to the 21–25 age group. However, the present data showed that 72.3% of the studied gym members were currently employed and received higher education, i.e., bachelor's degree or higher (67.1%). Moreover, the majority of the study participants were single (61%), and half of them (50.8%) drew income less than 5000 Saudi Riyal (SR) (Table 1).


**Table 1.** Sociodemographic characteristics (*n* = 541).

#### *3.2. Practices Associated with Androgenic–Anabolic Steroid Consumption*

As shown in Figure 1, the most commonly used AAS in our study across all ages were Anavar (61.9%), Dianabol (46%), and Deca Durabolin (45.1%).

– **Figure 1.** The prevalence of the most commonly used Androgenic–Anabolic Steroids (AAS) brands (generic).

Nearly 64.6% of gym members had been consuming AAS for more than 5 years, while 20.4% had been using steroids for three years or more (Figure 2).

–

**Figure 2.** The relationship Between Using of Steroids and Years of Practice.

The majority of the AAS users (77%) reported side effects, and 47% experienced psychiatric problems, including depression, insomnia, and lower appetite. Acne was reported in 32.7% and hair loss in 14.2% of participants, as shown in Table 2.



The prevalence of AAS users in this study was 21.3%. Furthermore, it was higher in the age group of 26–30 (31.9%), followed by the 21–25 group (27.4%). The majority of them were employed (82.3%) with low (less than 5000 SR) income (41.6%), as presented in Table 3. According to Figure 3, it appears that trainers and friends are a major source for obtaining AAS.

**Figure 3.** Sources of steroids.

*–*


**Table 3.** The prevalence of anabolic steroid use according to selected characteristics.

Approximately 63.7% of participating gym members observed an increase in activity, while 76.1% reported an increase in power after using AAS. However, 88.5% of users reported fast muscle mass gain (Figure 4).

**Figure 4.** Reported advantages of using anabolic steroids.

#### *3.3. Knowledge about and Attitude towards Androgenic–Anabolic Steroid Consumption*

*–* Surprisingly, the participants in our study were not aware of the potential adverse effects of AAS use. However, the majority of the AAS users had adequate knowledge of the adverse effects of AAS compared with nonusers. Approximately 38.1% of participants were aware that using AAS may lead to increased blood pressure, hair loss (34.5%), and acne (33.6%). Meanwhile, the nonusers expressed more knowledge of infertility (48.69%). About 18.6% of AAS users think that using AAS without a medical prescription is legal, while 15% did not know if it was legal to use ASS with a medical prescription or not. Among users, 66.4% believe it is illegal and still use it (Table 4).


**Table 4.** Knowledge about the adverse effects of anabolic steroids.

#### **4. Discussion**

In this study, we evaluated the prevalence, practices, knowledge, and attitudes of gym members in Eastern Province, Saudi Arabia, using AAS. The prevalence of AAS users among males attending gym centers was as high as 21.3%. These findings are in accordance with other studies conducted in the region (Kuwait and the UAE) [14,15]. Furthermore, two local studies were done in 2016 and 2017, in Riyadh [13] and Jazan [12], respectively. Both studies show an approximately 10% higher prevalence rate.

There are many reasons behind the prevalence of AAS consumption among gym members in the Eastern Province, such as competition among athletes to quickly build muscle mass. Respondents believed that the muscle growth advantages of AAS outweighed its adverse harmful effects [15], as the use of AAS makes lifting heavy objects easier [5]. Even some trainees recommended allowing the use of AAS for enhancing performance [16].

A local study found that the majority (77%) of athletes who self-declared AAS use and were aware of their adverse effects would still recommend them to friends [13]. Another reason for the high use rates could be due to the availability of AAS in gym centers and from trainers and friends. As reported recently, the prevalence of AAS consumption was highly influenced by its availability [16].

The highest prevalence of AAS usage in our study was among the 21–30 age group. This result is different from what was reported in Kuwait and the Middle East and North Africa (MENA) regional studies [15]. Similar profiles have been reported in other local studies, with the majority being the age group of 25 to 29 years [5,11].

In spite of the significant level of knowledge expressed in the study sample, the findings indicate a wide range of practices within the studied gym members. This suggested inadequate insight and a lack of healthcare professionals specializing in sports science who may be able to popularize an understanding of the wide range of adverse effects related to AAS use [7].

Our study revealed a negative association between monthly income and level of education with the prevalence of AAS use, which means that knowledge and education were independent of AAS use. Remarkably, these findings were also observed in previous studies that were performed in the region [5].

The most common types of AAS used in our findings were Anavar, Dianabol, and Deca Durabolin. This differed from previously reported data in another region of Saudi Arabi [17]. This could reflect the availability and preference for AAS in Saudi Arabia.

#### **5. Conclusions**

Based on this study, the prevalence of AAS users in Eastern Province, Saudi Arabia is high, which reflects the fact that gym members are at a higher risk of using AAS. Therefore, Regional Health Authorities in the Eastern Province region, Saudi Arabia, should urgently take measures to alleviate the potential adverse implications of AAS consumptions among

young adults by using social media as an educational tool, or by distributing informative leaflets among AAS users.

#### **6. Limitation**

Although this is the first study conducted on gym members in the Eastern Province regarding AAS consumption, it had some limitations. Notably, it was only performed among male gym members, no blood work was included to investigate potential adverse implications of AAS, and finally, we used a self-reported questionnaire.

**Author Contributions:** W.A.; Y.E. and N.J. made substantial contributions to the conception, design, and acquisition of data. Y.E.; N.J. and A.A. helped in the analysis and interpretation of data. D.B.; and M.A.-H. drafted the manuscript. All authors have read and agreed to the published version of the manuscript.

**Funding:** The authors received no specific funding for this work.

**Institutional Review Board Statement:** The study was conducted according to the guidelines of the Declaration of Helsinki, and approved by the Institutional Review Board of Imam Abdulrahman Bin Faisal University (IRB-2018-01-174, 27 September 2018).

**Informed Consent Statement:** Informed consent was obtained from all subjects involved in the study.

**Data Availability Statement:** The data used to support the findings of this study are available from the corresponding authors upon reasonable request.

**Conflicts of Interest:** The authors declare that they have no competing interests.

#### **References**


**Shirin Aali <sup>1</sup> , Farhad Rezazadeh 2 , Georgian Badicu <sup>3</sup> and Wilhelm Robert Grosz 3, \***


**Abstract:** *Background and Objectives*: Acquiring knowledge about the magnitude and direction of induced joint forces during modifying gait strategies is critical for proper exercise prescription. The present study aimed to evaluate whether a heel-first strike pattern during gait can affect the biomechanical characteristics of ankle and knee joints among asymptomatic people. *Materials and Methods*: In this cross-sectional study performed in the biomechanics laboratory, 13 professional healthy male athletes walked on an instrumented walkway under two walking conditions. For the normal condition, subjects were instructed to walk as they normally would. For the heel-first strike condition, subjects were instructed to walk with heel-first strike pattern and increase heel contact duration as much as possible. Then, knee and ankle joint range of motions and moments, as well as vertical ground reaction force was measured by the Kistler force plate and Vicon motion analysis system. *Results*: Knee flexion angle at the initial contact and during stance phase was significantly lower when increasing the heel strike pattern. In addition, the mean values of the knee external rotation and adductor moments during heel strike condition were lower than those in normal walking. Further, the ankle dorsiflexion range of motion (ROM) during mid-stance increased significantly during heel-first strike pattern compared to the value in normal gait pattern. *Conclusions*: The modification of gait pattern including heel-first strike pattern can reduce the mechanical load applied to the knee, while improving the extensibility of gastro-soleus muscle complex.

**Keywords:** biomechanics; heel strike; ankle; gait change; gastrocnemius muscle stiffness

#### **1. Introduction**

Excessive joint forces play a significant role in developing musculoskeletal system impairment and pain which are the major causes of disability and form a major part of the high costs of health care in the industrialized world [1,2]. In particular, limited ankle dorsiflexion range of motion (ROM) is associated with many of the lower extremity injuries such as anterior cruciate ligament ACL, Achilles, and patella tendon injuries [3,4]. The relationship between gastro-soleus complex stiffness and many of the clinical problems of the foot and other joints of the kinetic chain are well-documented, which cause syndromes of the movement system [5,6].

Previous studies confirm the theories related to the existing mechanics of limited ankle dorsiflexion ROM and the injury of the kinetic chain joints [7,8]. The decreased ankle dorsiflexion may decrease anterior tibial translation at the ankle joint during stance phase of the gait cycle [7] and result in lowering the center of gravity during functional tasks such as walking [9]. This may compensate through mid-foot and subtalar joint pronation, knee joint flexion and valgus, which are related to chronic and acute injuries including ACL rupture, patella-femoral pain syndrome (PFPS), and knee osteoarthritis [10]. Some studies reported increased knee flexion and knee valgus during functional movements.

**Citation:** Aali, S.; Rezazadeh, F.; Badicu, G.; Grosz, W.R. Effect of Heel-First Strike Gait on Knee and Ankle Mechanics. *Medicina* **2021**, *57*, 657. https://doi.org/10.3390/ medicina57070657

Academic Editor: Filipe Manuel Clemente

Received: 30 April 2021 Accepted: 23 June 2021 Published: 26 June 2021

**Publisher's Note:** MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

**Copyright:** © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

For example, walking among people with limited ankle dorsiflexion ROM supports this theory [8,11].

Further, limited ankle dorsiflexion ROM may increase the injury risk through changing the joint forces and muscle stiffness of the lower extremities. Accordingly, the reduced ankle dorsiflexion ROM and changes in knee and hip ROM resulted in increasing ground reaction forces, which are considered as the main causes of lower extremities injuries reported in the previous studies [12,13]. Another possibility is related to the relationship between limited ankle dorsiflexion and injuries through a series of mechanical compensatory patterns instead of a unique mechanical movement pattern in one joint. According to the dynamic system theory, they are considered as multiple biomechanical degrees of freedom recruiting variability as a common output. In addition, limited dorsiflexion may demonstrate loss of a biomechanical degree of freedom (movement pattern variability) which is related to various injuries in the overall kinetic chain [14,15].

Therefore, a good understanding of how gait strategies affect moment and joint forces may improve the results of therapeutic protocols. Acquiring knowledge about the magnitude and direction of induced joint forces during modifying gait strategies is critical for prescribing proper exercise. Modification may include a subtle change in lowerextremity position such as encouraging patients to walk with heel-first strike pattern and increasing heel contact duration as much as possible. Furthermore, it is documented that the musculoskeletal system is optimized subtly to minimize demanding stresses on bones and muscles; any improper change in the movement system, such as muscle imbalance or weakness, increases the joint forces significantly [16,17]. Thus, it is important to evaluate the effectiveness of joint forces from modifying gait patterns among people with gastrocnemius muscle stiffness.

Clinically speaking, the results of the previous studies indicated that the people with gastro-soleus muscle stiffness experienced increased peak foot pronation, knee valgus, magnitude of ground reaction forces, and knee adduction moment [18,19]. Therefore, it seems that changing the gait strategy with a simple guide, such as "walking with heel-first strike pattern and increasing heel contact duration as much as possible" during walking and the extensibility of gastro-soleus muscle complex is effective, especially for the patients with limited dorsiflexion and resulting pain in other joints of the kinetic chain (lower back pain) [17]. However, during the first step of designing a therapeutic protocol, it is unclear whether modifying gait pattern with a simple guide to "heel-first strike pattern" can reduce ground reaction forces, ankle dorsiflexion during the mid-stance phase of gait, knee flexion, knee external rotation, and adduction moment among the healthy people.

Thus, the present study aimed to investigate whether a heel-first strike pattern during gait can affect the selected kinetic and kinematic parameters of ankle and knee joint among healthy subjects. Principally, it is assumed that when a subject changes their gait pattern, the vertical ground reaction force, knee flexion angle during heel contact, mean ankle dorsiflexion during mid-stance, mean knee external rotation, and adduction moment are changed to reduce joint forces and the extensibility of the gastro-soleus muscle.

#### **2. Materials and Methods**

#### *2.1. Participants*

This cross-sectional study was performed on 13 professional competitive runners with five years of experience in the national athletics team (mean age = 25.2 ± 1.2, height = 179.9 ± 1.4 cm, weight = 76.6 ± 4.7 kg) which had normal dorsiflexion ROM in both legs. The mean ankle dorsiflexion AROM in the knee extension and flexion position was 14.4 ± 0.8 and 14.5 ± 0.9 degrees, respectively. The exclusion criteria included the history of trauma or ankle surgery, bone pathology, neurological disorders, and rheumatoid arthritis, inflammatory diseases, and any conditional abnormalities affecting the research process. The individuals recruited from the available community were selected by using the findings of a preliminary study to determine the sample size based on the variance of the test parameters among five participants.

Regarding the ethical consideration, all of the participants read and signed an approved informed consent letter before data collection. The study was confirmed by the Ethical Committee of the university. Participants had the right to decline to participate and withdraw from the research after initiating the process of data collection.

The dorsiflexion ROM was measured using a universal goniometer in both knee bending for soleus length, and extended knee for gastrocnemius length positions [16,17]. At least 10 degrees of ankle dorsiflexion are needed during the stance phase of the gait cycle, which can contribute to forward body movement for normal walking [5,6]. According to previous studies, the normal ankle dorsiflexion ROM should be ranged 10–15 degrees [20,21]. Therefore, at least 12 degrees was considered as the inclusion criterion for ankle dorsiflexion AROM.

#### *2.2. Gait Testing Procedures*

The participants underwent gait testing during a single data collection session. All procedures were carried out at Mowafaghian gait analysis laboratory of Sharif University of technology. Standard 9 mm retroreflective markers were placed over the anatomic landmarks including the heads of the first and fifth metatarsals, the posterior aspect of the calcaneus, and the medial and lateral malleoli, lateral knee joint lines, lateral epicondyle of femur, and anterior superior iliac spine, as well as laterally on shank and thigh of the affected foot determined by anatomic definitions from the Vicon Clinical Manager [19,22]. The position data of markers and ground reaction forces were processed with Vicon dynamic model using Plug-in-Gait-Workstation software version 4.3 (Oxford, UK) to generate the kinematic data and joint moment for sequential analysis.

In the next procedure, kinematic variables during walking were collected using a sixcamera, motion capture system (Motion Analysis MX40S, VICON, Oxford, UK) sampling at 120 Hz. Then, the ground reaction force data were collected from two floor-mounted Kistler force plates (30 × 50, Winterthur, Switzerland) positioned in the middle of the 6 m walkway and sampling at 1200 Hz. Accordingly, three trials with clean force platform strikes were obtained for the dominant limb. All walking trials were performed barefoot based on the participants' self-selected and preferred walking speed.

Each participant accomplished three trials per each condition. The first is related to self-selected or preferred speed walking (normal walking). In the second condition, they were guided to increase the heel strike during walking (walking with heel-first strike pattern) based on the cue "walk with heel-first strike pattern and increase heel contact duration as much as possible". They were given only this simple instruction without any feedback during the study.

In addition, practice trials were allowed until the participants walked comfortably and could contact the force plate with only one foot without altering their gait. Typically, three trials are performed for each situation as a practice. The stance phase was determined from the moment the heel touched the force plate until the toe was lifted off.

#### *2.3. Data Analysis*

The data were collected from at least three trials for each condition with clean foot strikes from each foot. Then, the moments of force were calculated by mathematical equations including inverse dynamic method and link-segment model [3,6]. To calculate the knee adduction and rotation moment, the knee moment was first calculated on the frontal and horizontal planes, and then the time series data of moment-time were normalized. The first 60% of normalized time series was considered as the stance phase. According to ISB recommendations, the positive and negative moments are considered as knee external rotation and adduction torques, respectively [3,14]. Further, joint moments were normalized to body mass (NM/kg). Furthermore, temporal parameters such as step length, walking speed, and total stance time were identified for each trial. Finally, an independent t-test was used to compare group differences after determining the normal distribution of data using the Shapiro–Wilk test and the equality of variances between groups by

using Levene's test. Statistical analysis was performed at the significance level of 0.05 and statistical power of 0.80 by SPSS software version 18.

#### **3. Results**

Table 1 indicates the mean and standard deviation for kinetic and kinematic variables, as well as spatiotemporal parameters of each group. Walking speed in normal walking is significantly greater than that of heel-first strike condition (*t* = 2.21, df = 12, *p* = 0.05). However, no significant difference was observed between the stance time and step length in two conditions (*t* = −0.071, df = 12, *p* = 0.94; *t* = −1.25, df = 12, *p* = 0.24, respectively). In addition, the mean values for the knee flexion-extension ROM during stance phase, knee flexion angle at initial contact, knee external rotation moment during stance phase were significantly higher in normal walking condition (*t* = 2.26, df = 12, *p* = 0.02; *t* = 3.37, df = 12, *p* = 0.005; *t* = 3.09, df = 12, *p* = 0.03, respectively). However, no significant difference was observed between the mean values for ankle dorsiflexion during stance phase in two conditions (*t* = 0.22, df = 12, *p* = 0.82). In addition, the mean ankle dorsiflexion during mid-stance was higher during walking with heel-first strike compared to normal walking (*t* = −2.37, df = 12, *p* = 0.04).

**Table 1.** The mean (standard deviation) for kinetic, kinematic, and spatiotemporal parameters.


ROM: range of motion; \* indicates statistical significance.

Table 2 indicates the mean and standard deviation of vertical ground-reaction force parameters. The mean value for the peak vertical force at the initial contact was significantly higher during walking with heel-first strike (*t* = −2.88, df = 12, *p* = 0.01). Further, no significant difference was reported between the mean value for peak vertical force during weight bearing in two conditions (*t* = 0.78, df = 12, *p* = 0.45). However, the mean value for peak vertical force during toe-off motion was greater during walking with heel-first strike than during the normal walking condition (*t*= −4.38, df = 12, *p* = 0.002).


**Table 2.** The mean (standard deviation) of ground reaction force parameters (data expressed as percentage of stance phase time). **'**

\* indicates statistical significance.

#### **4. Discussion**

The results indicated that the ankle dorsiflexion ROM during the stance phase was greater in heel-first strike compared to the normal walking trial. Furthermore, the parameters of ground reaction force during walking with heel-first strike pattern were significantly higher than those in normal walking (Figure 1). The results could support the theory that heel-first strike during walking leads to a decrease in knee flexion angle at the initial contact and stance phase (Figure 2). In addition, two kinetic variables including the knee external rotation and adduction moment were significantly lower with increased heel-first strike trial (Figure 3). However, the spatiotemporal parameters such as step length and total stance phase time were not significantly different between trials, while walking speed in normal walking was significantly higher than walking with heel-first strike pattern condition.

**Figure 1.** Ground reaction force during increased heel strike gait and normal gait during stance phase.

**Figure 2.** Joint angle patterns (degree) of healthy athletes with increased heel strike gait and normal gait during stance phase. (**a**,**b**): ankle joint angles in the sagittal and frontal plane, respectively. (**c**,**d**): knee joint angles in the sagittal and frontal planes, respectively.

Based on the results, the ground reaction forces, especially the peak impact with heel-first strike walking trial, were significantly greater than the normal walking trial (Figure 1). The findings are consistent with those of [23], which reported increased ground reaction forces in the athletes with the heel strike gait pattern. Grieve et al. [22,24] reported increased ground reaction forces due to the ankle kinematic changes, which are in line with the findings of the present study. In this study, changing the gait pattern with heel-first strike pattern resulted in changing the ground reaction force and knee joint kinematics. On the other hand, the walking speed in normal walking was significantly higher than walking with heel-first strike pattern condition (Table 1), which can be explained by increasing the heel contact duration in the walking with heel-first strike pattern condition rather than normal walking. In addition, walking with heel-first strike pattern changed the kinematics of the knee joint since a reduced inertia led to a compensatory change in the gait kinematics. However, the lack of studies in this area has created some difficulties for interpreting the results.

**Figure 3.** Joint moment pattern (N.M/Kg) of healthy athletes with increased heel strike gait and normal gait during stance phase. (**a**,**b**): ankle moment in the horizontal and frontal planes, respectively. (**c**,**d**): knee joint moment in the horizontal and frontal planes, respectively.

As displayed in Figure 2, knee flexion angle at the initial contact and the knee flexion ROM during the stance phase with heel-first strike pattern walking trial were significantly lower than those in the normal walking. Thus, the significance of the heel strike effect on ground reaction forces should be determined along with demonstrating the heel strike effect changing the knee joint kinematics in the sagittal plane. As a result, the knee and hip joints run into a more flexion position among the people with gastro-soleus stiffness compared to those in healthy people. This position puts the knee in the unlocked position leading to insufficient knee motor control, and compensatory movement patterns in the hip joint (recruiting increased hip extensor muscles and appearing to show synergistic dominance of the hamstring and gluteal muscles). Therefore, it seems that utilizing the cue "increase the heel contact duration" can change the knee flexion position during stance phase, and consequently, modify the insufficient motor control of the lower extremities.

. It is believed that healthy people have a translation of tibia over the ankle joint during the stance phase of gait needed for forward propulsion. Despite the lack of significant difference of mean ankle dorsiflexion during stance phase between the trials, the mean ankle dorsiflexion ROM during mid-stance with heel-first strike pattern walking trial was significantly higher than that of normal walking (Figure 2). The finding of this pilot study may confirm that the heel-first strike walking pattern, as a functional pattern, can be effective in promoting the extensibility of the gastro-soleus muscle.

Furthermore, the values of the ground reaction force failed to decrease significantly in heel-first strike walking trial compared with those in normal walking. Thus, it is worth noting that gait strategies should be modified to achieve a special purpose, not as a set of positive effects. For example, increasing the ankle dorsiflexion ROM and decreasing the knee flexion angle for the individuals with gastro-soleus tightness are more essential than increasing ground reaction forces during walking with heel-first strike pattern since limited ankle dorsiflexion and increased knee flexion are considered as the risk factors for musculoskeletal injuries, such as patellofemoral pain syndrome, osteoarthritis, as well as synergistic dominance of hamstring muscles [10,15,16].

The results indicated that the mean external rotation and adduction moment of the knee in the heel-first strike pattern gait trial decreased significantly compared with those in a normal gait (Figure 3). In the present study, the knee external rotation and adduction moment were measured to identify and establish a movement pattern for the purpose of decreasing mechanical loading on the knee through the guidance to heel-first strike pattern since the improper loading of the knee is regarded as a risk factor for the knee osteoarthritis among the people with gastro-soleus tightness based on the literature [10,20]. In particular, medial knee compartment loading is considered as a clinical indication of the knee injuries and the knee external rotation and adduction moments are mentioned as an indirect measure of the medial knee compartment loading during functional tasks such as walking in most of the recent studies [20,21]. Therefore, early detection of the risk factors involved in knee osteoarthritis, as well as identifying the effective movement pattern for reducing the knee external rotation and adduction moment values may be more successful with the effectiveness of exercise interventions and preventing structural changes in the knee joint. Based on the results of the present study, walking with a heel-first strike pattern can reduce the loading forces of the knee joint. However, the findings cannot be generalized to those with gastro-soleus tightness. Therefore, further research is needed to ensure the effectiveness of heel-first strike gait pattern on reducing mechanical loading on the kinetic chain in people with gastro-soleus tightness.

#### **5. Conclusions**

Based on the results, heel-first strike gait pattern in healthy athletes could make kinematic changes in the knee and ankle joints in all three movement planes. For example, knee flexion angle at the initial contact and the knee flexion ROM during the stance phase decreased with heel-first strike pattern walking. Additionally, some kinetic changes including the mean values of the knee external rotation and adductor moments during heel strike condition were lower than those in normal walking. In addition, heel-first strike gait pattern with increased ankle dorsiflexion at the heel contact led to the extensibility of gastro-soleus muscle complex.

The main limitation is that the participants had no limited dorsiflexion ROM. Thus, the people with gastro-soleus tightness failed to respond to heel-first strike gait pattern like normal people. The present pilot study aimed to evaluate the concept of heel-first strike gait pattern for decreasing knee flexion, increasing ankle dorsiflexion, minimizing knee external rotation and adduction moment during gait, and applying the pattern in people with gastro-soleus tightness. By confirming the heel-first strike gait pattern effect on kinematic changes in this study, another study can be conducted on applying heel strike gait in the athletes with gastro-soleus tightness.

**Author Contributions:** S.A. and F.R. conceived and designed the experiments; S.A. performed the experiments; F.R., G.B. and W.R.G. analyzed the data; S.A. and F.R. contributed reagents and materials; S.A., F.R., G.B. and W.R.G. wrote the paper. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

**Institutional Review Board Statement:** The study was conducted according to the guidelines of the Declaration of Helsinki, and approved by the Ardabil University of Medical Sciences (protocol code: IR.ARUMS.REC.1400.95 and date of approval: 10 November 2020).

**Informed Consent Statement:** Informed consent was obtained from all subjects involved in the study.

**Data Availability Statement:** The data presented in this study are available on request from the author Farhad Rezazadeh.

**Acknowledgments:** Thanks to numerous individuals who participated in this study.

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **References**

