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Article

EMG Activity of Lower Limb Muscles during Anti-Gravity Treadmill Running with Different Loads and Speeds

by
Przemysław Pietraszewski
*,
Artur Gołaś
,
Robert Roczniok
,
Mariola Gepfert
and
Adam Zając
Institute of Sport Sciences, The Jerzy Kukuczka Academy of Physical Education in Katowice, 40-065 Katowice, Poland
*
Author to whom correspondence should be addressed.
Appl. Sci. 2024, 14(17), 7518; https://doi.org/10.3390/app14177518
Submission received: 27 July 2024 / Revised: 22 August 2024 / Accepted: 23 August 2024 / Published: 25 August 2024
Browse Figure
Versions Notes

Abstract

:
The study’s objective was to identify the features of internal movement structure that depend on speed and the importance of unloading when jogging on an anti-gravity treadmill. The aim was to investigate whether the internal structure of running changes under unloaded conditions, using an anti-gravity treadmill. Twenty male competitive middle- and long-distance runners with the following characteristics participated in the study: age, 25 ± 5 years; body weight, 67.2 ± 8.9 kg; body height, 177 ± 11 cm; and training experience, 9 ± 5 years. The gastrocnemius (GC), tibialis anterior (T), quadriceps femoris (Q), biceps femoris (B), and gluteus (G) were the five lower limb muscles whose muscle activity was evaluated. Surface electromyography (sEMG) was used to measure muscle activation while jogging and running on the AlterG Anti-Gravity Treadmill. The study method involved capturing the examined muscular activity at four different speeds: 6, 10, 14, and 18 km/h. At each of these speeds, four two-minute measurements were taken with varying body weight relief: 100%, 75%, 50%, and 25% of body weight. Repeated measures multivariate analysis of variance (RM-MANOVA) [F = 3.4663 p = 0.0001] showed that as running speed increases, the muscular activity of each muscle, expressed as a percentage of maximum muscle tension (%MVIC), decreases significantly. Results indicate that running pace affects the dynamics of the reduction in muscle activity in every examined muscle. As one runs faster, the decline in dynamics becomes more intense. At the slowest jogging pace (6 km/h), the variations were almost negligible (±4 percentage points between 25% and 100% body weight relief) as unloading increased. However, the discrepancies reached up to 14 percentage points at the fastest running speed (18 km/h). In every muscle studied, distinctive patterns and significant dynamics at high speeds were observed. The study’s findings suggest that using an anti-gravity treadmill for training can be beneficial, yet it is important to consider the significant relationships between speed and relief, as these variables could impact maintaining a proper movement pattern and running style. This knowledge may be useful when choosing the right training regimens and loads for runners recovering from injuries.

1. Introduction

Running is one of the most common physical activities. In comparison to other sports, it does not require advanced and expensive equipment and can be practiced by people of any age and physical condition. However, the popularity of running is also associated with a high risk of injuries, among both professional runners and amateurs. It has been estimated that, annually, 27–70% of people training for competitive or recreational reasons suffer injuries as a result of overloading [1,2,3]. It has been proven that the application of customized anti-gravity treadmill training positively impacts the rehabilitation of stroke patients, underscoring the importance of selecting a treatment method tailored to the specific needs of each patient [4]. Although the exact mechanisms of these overload injuries have not been specified, it has been found that one of their most probable causes might be the magnitude of the ground reaction forces affecting a runner [5,6,7,8,9]. The search for appropriate training methods to support physical effort focuses not only on the muscles that generate movement, but also on the respiratory muscles [10].
Therefore, it seems worthwhile to look for an alternative training method that can help minimize the risk of injuries and decrease lower limb ground reaction forces. Numerous studies are being conducted on the structure of muscle work during running and sprinting [11,12]. One of the components of these reaction forces is the impact force, which is defined as a local maximum force observed during the heel–toe running strategy. The magnitude of the impact force can be altered by changing stride length [13], footstrike pattern [14,15,16], speed [17,18], and running surface [19]. It can be eliminated completely by running in deep water, where the runner’s feet do not touch the ground [20]. Until recently, weight alleviation training has been practiced in water or with the use of various types of harnesses. A person running in deep water runs while wearing specific swimming equipment, in a deep pool, without touching the bottom with their feet. When performing this type of training, the body is supported by the water buoyancy forces; thus, the athlete’s body weight is reduced to almost zero. Although studies on the subject, reviewed by Reilly et al. [21], showed that running in deep water can help maintain performance on land, many deep water training programs have been shown to be ineffective. Deep water movements can help maintain aerobic fitness, but neuromuscular training and movement patterns are very different from normal movements because the forces applied to the body in water are disproportionate to the forces involved in surface movements.
An alternative to this type of physical activity may be the use of an anti-gravity treadmill. The Alter-G lower body positive pressure treadmill, also known as the anti-gravity treadmill, is a device dedicated not only to athletes but also to people struggling with overweight or undergoing rehabilitation after lower limb injuries. The anti-gravity treadmill is designed to reduce pressure on joints, tendons, and ligaments while running or walking [22] by limiting the ground reaction forces. It was shown that using the anti-gravity treadmill can effectively preserve the mechanics of gait while reducing the ground reaction forces on lower limbs in postoperative patients. This device is connected to a pressure chamber filled with air, which surrounds an exercising person from the waist down. The anti-gravity treadmill is able to support body weight from 0% to even 100%. The exerciser wears neoprene shorts that are tightly attached to the pressure chamber. After completing all the preliminary steps, the treadmill is calibrated, and the appropriate weight and speed are adjusted.
Despite being a relatively new technology, numerous studies have examined the effects of using an anti-gravity treadmill on the runner’s body, demonstrating its benefits for injury prevention and rehabilitation. It has been found that the greatest differences in muscle activity were detected after changing running speed, while changes in inclination and body weight had less impact on muscle activity. Lower muscle activation has been reported for all downhill conditions, with more tightly clustered low activation levels that were not affected by incline, speed, and body weight [23]. Some researchers paid more attention to the activation of hamstrings while running on the anti-gravity treadmill. Their results have revealed that increased speed on the treadmill resulted in higher peak activation in all the tested muscles, while body weight had a lower influence on changes in muscle activity. The hamstrings were activated before and after the heel strike during a fast run on an anti-gravity treadmill. The lateral hamstrings were more active than the medial hamstrings throughout the gait cycle, especially in the stance phase [23]. In turn, Liebenberg [24] conducted an experiment which has demonstrated that reducing body weight with the anti-gravity treadmill caused a decrease in muscle activity. In addition, muscle activity increased with higher running speed, maintaining the muscle activity patterns despite changes in speed or weight. If the goal of training on an anti-gravity treadmill was to match the muscle activity to that of running on land, the exercising person would have to run at increased speed with less weight. However, if the aim of exercise on this treadmill is to maintain a specific pattern of muscle activity, then the range of body weight can be set to between 60 and 90%, because body weight does not significantly affect changes in muscle activity patterns during running [24]. Lower extremity muscle activity was also tested by Mercer [25] at 20% and 50% of normal body weight. The study found that the activity of the major muscles of the lower extremities decreased as weight decreased and increased as speed increased for all possible body weights. In contrast, the percent change in muscle activity was much smaller compared to the percent change in body weight [26].
The aim of the study was to determine whether the internal structure of running changes under unloaded conditions using an anti-gravity treadmill. It is assumed that conditions of reduced gravity may significantly influence the change in running structure and technique; however, under certain conditions, unloading may have a neutral effect.

2. Materials and Methods

2.1. Participants

Twenty male competitive middle- and long-distance runners with the following characteristics participated in the study: age, 25 ± 5 years; body weight, 67.2 ± 8.9 kg; body height, 177 ± 11 cm; and training experience, 9 ± 5 years. Each participant had at least 10 years of running training experience and had competed in national or international competitions. All participants were healthy and reported no injuries in the past six months. Prior to the experiment, the runners underwent a 48 h rest period, during which they were instructed to maintain their regular diet and hydration. All the participants were informed verbally and in writing about the procedures, possible risks and benefits of the tests and provided written consent before the commencement of the study. The study received the approval of the Bioethical Committee of the Academy of Physical Education in Katowice (3/2021) and was performed according to the ethical standards of the Declaration of Helsinki, 2013.

2.2. Procedures

The measurements were performed in the Strength and Power Laboratory at the Academy of Physical Education in Katowice. The study method involved capturing the examined muscles’ activity at four different speeds: 6, 10, 14 and 18 km/h. At each of these speeds, four 2 min measurements were taken with varying body weight relief: 100%, 75%, 50%, and 25% of body weight. The test started with a standard 15 min warm-up, which included continuous running, joint mobility, static and dynamic stretching of the lower and upper limbs and 3–4 repetitions of 30 s runs at progressive speed on the anti-gravity treadmill.
The anti-gravity treadmill (AlterG Anti-Gravity TreadmillTM M320) operates using positive pressure generated by compressed air within a sealed structure. This enclosed system encompasses the lower half of the user’s body. The treadmill itself is covered by an air-tight inflatable bag, and the user wears special shorts equipped with a half-zipper around the hips. This zipper connects to the top of the inflatable bag. The bag is secured to support poles on either side, which run parallel to the sides of the zipper and can be adjusted vertically within the treadmill’s outer frame. This vertical adjustability accommodates users of varying heights and allows for precise control of body weight support. The anti-gravity treadmill can provide support for up to 80% of the user’s body weight.

2.3. Electromyography

The Noraxon TeleMyo 2400 recording system, with eight channels, was employed to capture biopotentials from muscles during each repetition of the jogging and running on the anti-gravity treadmill. Five muscles—the gastrocnemius (GC), tibialis anterior (T), quadriceps femoris (Q), biceps femoris (B), and gluteus (G)—were monitored. Preceding electrode placement, skin preparation involved shaving, abrasion, and alcohol cleansing. Electrodes (Dri-Stick Silver circular sEMG Electrodes AE-131, NeuroDyne Medical, Cambridge, MA, USA) were then positioned in accordance with SENIAM procedures [27], spaced 2 cm apart with an 11 mm contact diameter. sEMG signals, sampled at 1000 Hz, underwent bandpass filtering (8 Hz to 450 Hz) followed by root-mean-square (RMS) calculation. Before and after the experimental session, MVIC tests were conducted, with the highest value chosen for analysis, expressed as a percentage of maximum voluntary isometric contraction (%MVIC). Tests utilized with two 5 s maximum isometric contractions separated by a 10 s rest interval, and a 2 min rest interval between MVC evaluations per muscle, adhering to SENIAM procedures. The sEMG data were based on the average of the peak sEMG amplitude recorded across the trials for each muscle [28].

2.4. Statistical Analysis

All analyses were performed using the Statistica 13.1 package. The normality of distributions was verified using the Shapiro–Wilk test, the Levene test was used to verify the homogeneity of variances, and the Mauchly test was used to verify sphericity. The results were presented as means with standard deviations and 95% confidence intervals. A multicriterial repeated measures ANOVA was used to compare the differences between the considered variables. Effect sizes for main effects and interactions were determined by partial eta squared (η2). The ES were classified as small (0.01 to 0.059), moderate (0.06 to 0.137), and large (>0.137). In case of significant differences for main effect or interaction, post hoc comparisons were conducted using Bonferroni’s post hoc test. The statistical significance of the differences between the type of loads and muscle side was set at p < 0.05. Effect sizes (Cohen’s d) were also calculated. The ES was interpreted as large for d > 0.8, moderate for d between 0.8 and 0.5, and small for d < 0.5.

3. Results

Multicriterial repeated measures ANOVA indicated significant differences for main effects (Muscle F = 23.84, p < 0.0001, η2 = 0.20; Speed F = 537.58, p < 0.0001, η2 = 0.81; Body weight relief F = 1170.49, p < 0.0001, η2 = 0.75) and interactions (Body weight relief × Muscle F = 7.91, p < 0.0001, η2 = 0.076; Body weight relief × Speed F = 94.61, p < 0.0001, η2 = 0.43; Body weight relief × Muscle × Speed F = 3.47, p < 0.0001, η2 = 0.098). No significant differences were found for the interaction Muscle × Speed (F = 1.56, p = 0.099, η2 = 0.047). To verify between which interactions significant differences occurred, multiple comparisons post hoc Bonferroni tests were applied. As a result of the conducted analyses, a clear trend was observed. In each of the analyzed muscles, along with the increasing relief, the muscle tension value also decreased. However, more importantly, the dynamics of the tension decrease were significantly greater at higher speeds. The observed trend is presented in Figure 1.
For the gastrocnemius muscle, descriptive statistics are presented in Table 1. At a running speed on a treadmill of 6 km/h, significantly higher MVIC results [%] were found for 100% Body weight relief (m = 11.29 ± 1.50) compared to 25% Body weight relief (m = 8.98 ± 1.53; p = 0.029; d = 1.52). In the case of other interactions, no differences were found to be p > 0.05. At a running speed on a treadmill of 10 km/h, statistically significantly higher MVIC results [%] were found only for 100% Body weight relief (m = 16.75 ± 2.73) compared to 50% Body weight relief (m = 13.45 ± 1.02, p < 0.0001, d = 1.60) and compared to 25% Body weight relief (m = 12.71 ± 1.80, p < 0.0001, d = 1.75). In the case of other interactions, no differences were found to be p > 0.05. At a running speed on a treadmill of 14 km/h, statistically significantly higher MVIC results [%] were found for 100% Body weight relief (m = 22.55 ± 3.41) compared to 75% Body weight relief (m = 19.11 ± 2.82, p < 0.0001, d = 1.10), 50% Body weight relief (m = 17.58 ± 2.09 p < 0.0001 d = 1.76), and 25% Body weight relief (m = 15.99 ± 1.85; p < 0.0001 d = 2.39). No significant differences were found between 75% and 50% and between 50% and 25% Body weight relief at p > 0.05. At a running speed on a treadmill of 18 km/h, significantly higher MVIC results [%] were found for 100% Body weight relief (m = 28.51 ± 3.37) compared to 75% Body weight relief (m = 24.90 ± 3.40 p < 0.0001; d = 1.07), 50% Body weight relief (m = 22.04 ± 3.32 p < 0.0001; d = 1.93) and 25% Body weight relief (m = 19.92 ± 2.67; p < 0.0001; d = 3.67). There were only no significant differences between 50% and 25% Body weight relief.
For the tibialis anterior muscle, descriptive statistics are presented in Table 2. At a treadmill running speed of 6 km/h, statistically significantly higher MVIC results [%] were found for 100% Body weight relief (m = 11.87 ± 1.65) compared to 50% Body weight relief (m = 9.58 ± 1.62; p = 0.032; d = 1.40) and compared to 25% Body weight relief (m = 9.25 ± 1.54; p = 0.0014; d = 1.64). In the case of other interactions, no differences were found to be p > 0.05. At a running speed on a treadmill of 10 km/h, statistically significantly higher MVIC results [%] were found for 100% Body weight relief (m = 18.43 ± 2.68) compared to 75% Body weight relief (m = 15.92 ± 2.31; p = 0.0044; d = 1.00) compared to 50% Body weight relief (m = 14.08 ± 2.10; p < 0.0001; d = 1.81) and compared to 25% Body weight relief (m = 12.55 ± 2.04; p < 0.0001; d = 2.47). In the case of other interactions, no differences were found to be p > 0.05. At a running speed on a treadmill of 14 km/h, statistically significantly higher MVIC results [%] were found for 100% Body weight relief (m = 23.69 ± 2.44) compared to 75% Body weight relief (m = 20.46 ± 2.50; p < 0.0001; d = 1.31), 50% Body weight relief (m = 17.92 ± 2.04; p < 0.0001; d = 2.57) and 25% Body weight relief (m = 16.09 ± 1.81; p < 0.0001; d = 3.38). No significant differences were found between only 50% and 25% Body weight relief p > 0.05. At a running speed on a treadmill of 18 km/h, statistically significantly higher MVIC results [%] were found for 100% Body weight relief (m = 29.51 ± 2.63) compared to 75% Body weight relief (m = 25.62 ± 2.94; p < 0.0001; d = 1.39), 50% Body weight relief (m = 22.68 ± 2.45; p < 0.0001; d = 2.69) and 25% Body weight relief (m = 20.17 ± 2.27; p < 0.0001; d = 3.80). Significant differences were also found between the results of 75%, 50% and 25%, and between 50% and 25% Body weight relief p < 0.05
For the rectus muscle, descriptive statistics are presented in Table 3. At a treadmill running speed of 6 km/h, no significant differences in MVIC [%] were found due to Body weight relief (p > 0.05). At a running speed on a treadmill of 10 km/h, statistically significantly higher MVIC results [%] were found for 100% Body weight relief (m = 14.53 ± 3.92) compared to 75% Body weight relief (m = 12.14 ± 2.59; p = 0.013; d = 0.72), 50% Body weight relief (m = 10.60 ± 1.91; p < 0.0001; d = 1.27) and 25% Body weight relief (m = 8.96 ± 1.71; p < 0.0001; d = 1.84). In the case of other interactions, no differences were found (p > 0.05). At a running speed on a treadmill of 14 km/h, statistically significantly higher MVIC results [%] were found for 100% Body weight relief (m = 21.03 ± 5.21) compared to 75% Body weight relief (m = 16.53 ± 3.09; p < 0.0001; d = 1.05), 50% Body weight relief (m = 13.70 ± 2.42; p < 0.0001; d = 1.80) and 25% Body weight relief (m = 11.35 ± 2.06; p < 0.0001; d = 2.44). Significant differences were also found between the results of 75%, 50% and 25% and between 50% and 25% Body weight relief (p < 0.05). At a running speed on a treadmill of 18 km/h, statistically significantly higher MVIC results [%] were found for 100% Body weight relief (m = 28.39 ± 6.48) compared to 75% Body weight relief (m = 20.07 ± 3.28; p < 0.0001; d = 1.62), 50% Body weight relief (m = 17.33 ± 2.34; p < 0.0001; d = 2.27) and 25% Body weight relief (m = 14.49 ± 2.46; p < 0.0001; d = 2.84). Significant differences were also found between the results of 75%, 50% and 25% and between 50% and 25% Body weight relief (p < 0.05).
For the biceps femoris muscle, descriptive statistics are presented in Table 4. At a running speed of 6 km/h on a treadmill, no significant differences in MVIC [%] were found due to Body weight relief (p > 0.05). At a running speed on a treadmill of 10 km/h, statistically significantly higher MVIC results [%] were found for 100% Body weight relief (m = 15.60 ± 1.80) compared to 50% Body weight relief (m = 13.75 ± 1.37; p < 0.0001; d = 1.16) and compared to 25% Body weight relief (m = 12.50 ± 1.36; p < 0.0001; d = 1.94). In the case of other interactions, no differences were found (p > 0.05). At a running speed on a treadmill of 14 km/h, statistically significantly higher MVIC results [%] were found for 100% Body weight relief (m = 21.76 ± 1.98) compared to 75% Body weight relief (m = 19.20 ± 2.28; p = 0.0025; d = 1.20), 50% Body weight relief (m = 16.60 ± 1.79; p < 0.0001; d = 2.73) and 25% Body weight relief (m = 13.96 ± 1.92; p < 0.0001; d = 4.00). Significant differences were also found between the results of 75%, 50% and 25% and between 50% and 25% Body weight relief (p < 0.05). At a running speed on a treadmill of 18 km/h, statistically significantly higher MVIC results [%] were found for 100% Body weight relief (m = 26.88 ± 3.15) compared to 75% Body weight relief (m = 24.46 ± 2.78; p = 0.0094; d = 0.81), 50% Body weight relief (m = 21.71 ± 1.91; p < 0.0001; d = 1.98) and 25% Body weight relief (m = 18.43 ± 1.92; p < 0.0001; d = 3.24). Significant differences were also found between the results of 75%, 50% and 25% and between 50% and 25% Body weight relief p < 0.05.
For the gluteus maximus muscle, descriptive statistics are presented in Table 5. At a treadmill running speed of 6 km/h, no significant differences in MVIC [%] were found due to Body weight relief (p > 0.05). At a running speed on a treadmill of 10 km/h, statistically significantly higher MVIC results [%] were found for 100% Body weight relief (m = 18.90 ± 4.88) compared to 75% Body weight relief (m = 15.47 ± 4.46; p < 0.0001; d = 0.73), 50% Body weight relief (m = 13.31 ± 3.46; p < 0.0001; d = 1.32) and 25% Body weight relief (m = 11.30 ± 3.28; p < 0.0001; d = 1.83). In the case of other interactions, no differences were found (p > 0.05). At a running speed on a treadmill of 14 km/h, statistically significantly higher MVIC results [%] were found for 100% Body weight relief (m = 25.40 ± 6.22) compared to 75% Body weight relief (m = 20.16 ± 5.32; p < 0.0001; d = 0.91), 50% Body weight relief (m = 17.66 ± 4.16; p < 0.0001; d = 1.46) and 25% Body weight relief (m = 14.82 ± 3.93; p < 0.0001; d = 2.03). Significant differences were also found between the results of 75%, 50% and 25% and between 50% and 25% Body weight relief (p < 0.05). At a running speed on a treadmill of 18 km/h, statistically significantly higher MVIC results [%] were found for 100% Body weight relief (m = 31.11 ± 7.78) compared to 75% Body weight relief (m = 25.48 ± 6.56; p < 0.0001; d = 0.78), 50% Body weight relief (m = 23.23 ± 6.03; p < 0.0001; d = 1.13) and 25% Body weight relief (m = 19.49 ± 5.90; p < 0.0001; d = 1.68). Significant differences were also found between the results of 75%, 50% and 25% and between 50% and 25% Body weight relief (p < 0.05).

4. Discussion

The results obtained in our study unequivocally indicate that the pattern of muscle activity during running with unloading varies depending on running speed and the degree of unloading. However, these differences are not typically linear, and their dynamics depend on running speed. An increase in speed and degree of unloading results in much faster declines in muscle activity. At low speeds (6–10 km/h), the differences in muscle activity with increasing unloading were small enough to maintain an appropriate muscle activity pattern during running. At higher speeds (14–18 km/h), progressive unloading caused significantly greater decreases in muscle activity. This relationship clearly indicates that the use of an anti-gravity treadmill in training or post-injury rehabilitation is most beneficial at low running speeds. It allows for the application of high levels of unloading while maintaining a relatively standard muscle activity pattern. This can be particularly important for the recovery of individuals with lower limb injuries in the early stages of rehabilitation.
There are other studies which show that anti-gravity treadmills, like the AlterG®, have significant applications in sports, particularly for rehabilitation and recovery from injuries. They help maintain fitness while minimizing the adverse effects of unloading, which is especially important for endurance athletes. Reducing body weight load enables safe training with higher intensity, while decreasing the impact on bones and soft tissues. At higher running speeds, they can produce metabolic demands comparable to running at full body weight [29]. Such outcomes have been reported by other researchers [30]. Anti-gravity treadmills cause reductions in cadence, ground reaction forces (GRFs), GRF impulses, knee and ankle range of motion, and vertical stiffness, with elevations in stride length, flight time, ground contact time, and plantarflexion. It has also been noted that body weight support alters biomechanical variables such as cadence, stride length, and muscle activity, which should be monitored to avoid permanent changes in running form. Despite this, the anti-gravity treadmill significantly reduces ground reaction forces while maintaining running form, making it easier to return to full activity [31]. Barnes [32] investigated the physiological and biomechanical responses of highly trained distance runners to lower body positive pressure treadmill running, often referred to as anti-gravity treadmill training. The research focused on differences in body load and gait characteristics, concluding that such training can modify running biomechanics. This is especially beneficial for runners who wish to increase training intensity while minimizing injury risk.
The issue of muscle activity patterns while running on an anti-gravity treadmill has been thoroughly discussed in many studies. The variations in muscle activity with different levels of unweighting are complex and not consistent across various muscle groups [24,33,34]. Earlier studies have shown that, in healthy runners, there is a general reduction in muscle activity of the biceps femoris, rectus femoris, tibialis anterior, and gastrocnemius with progressive unloading. Additionally, muscle activity is higher at speeds of 115–125% of the preferred running speed, regardless of the level of unweighting. Surface electromyography (sEMG) measurements of lower extremity muscles (gastrocnemius medialis and lateralis, tibialis anterior, and vastus medialis and lateralis) during running with body weight support (BWS) reveal that preactivation levels do not change with unweighting. This consistency is believed to be due to maintained muscle preactivation, which counteracts the anticipated impact from a longer flight time.
Other researchers have reported nearly linear reductions in the activity of the rectus femoris, vastus medialis and lateralis, gastrocnemius, and soleus muscles with 20% increases in BWS [35]. However, during the braking and push-off phases, the muscle activity of the soleus and gastrocnemius (both medial and lateral) decreased by 10–20% as BWS increased. Moreover, increasing the cadence by 10% from the preferred habitual value boosts the muscle activity of the rectus femoris, biceps femoris, and tibialis anterior, regardless of the BWS level. Therefore, manipulating cadence may be an effective strategy to preserve more natural muscle activation patterns during rehabilitation with unweighting.
In accordance with the literature, the zero-crossing rate (ZCR) and amplitude of muscle tension (AMT) can quantitatively assess muscle fatigue from EMG signals [36]. However, in this study, muscle fatigue parameters were not used as evaluation criteria because the test protocol, both in terms of exercise volume and intensity, was designed to ensure that the athletes did not experience muscle fatigue. Future studies should involve higher training intensity and volume, and the analysis should include additional measurements of fatigue using signal frequency analysis, supplemented by isometric conditions.

5. Conclusions

The findings of this study, along with supporting evidence from other research, emphasize the critical role of running speed and degree of unloading in determining muscle activity patterns when using an anti-gravity treadmill. The relationship between speed and unloading is non-linear, with higher speeds causing more pronounced reductions in muscle activity. This suggests that the use of an anti-gravity treadmill is most beneficial at lower running speeds, where significant unweighting can be applied without disrupting the natural muscle activation patterns. This makes the technology particularly valuable in early rehabilitation for individuals recovering from lower limb injuries. While anti-gravity treadmills effectively reduce the mechanical load on the musculoskeletal system and minimize the risk of further injury, they also allow athletes to maintain fitness and train at higher intensities with reduced impact on bones and soft tissues. However, the influence of body weight support on biomechanical variables, such as cadence and stride length, should be closely monitored to prevent long-term changes in running form. The ability to manipulate cadence during unweighting offers an additional method to preserve more natural muscle activation patterns during rehabilitation.
In conclusion, anti-gravity treadmills provide a versatile and effective tool for both rehabilitation and athletic training, enabling safe and progressive recovery while minimizing injury risk. These treadmills allow for adjustments that optimize muscle activity and running mechanics, which is particularly beneficial in the early stages of recovery and for endurance athletes looking to maintain performance while reducing impact-related stress.

Author Contributions

Conceptualization, P.P. and A.G.; methodology, P.P. and A.G.; software, M.G.; validation, R.R. formal analysis, R.R.; investigation, P.P.; resources, R.R.; data curation, R.R.; writing—original draft preparation, P.P.; writing—review and editing, M.G.; visualization, A.Z.; supervision, A.Z.; project administration, P.P.; funding acquisition, A.Z. 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 research was approved by the Ethics Committee of The Academy of Physical Education in Katowice (3/2021) and executed according to the ethical standards of the latest version of the Declaration of Helsinki, 2013.

Informed Consent Statement

Informed consent was obtained from all subjects involved in the study. Written informed consent has been obtained from the patient to publish this paper.

Data Availability Statement

The datasets used and analyzed during the current study are available from the corresponding author upon reasonable request.

Conflicts of Interest

The authors declare no conflicts of interest.

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Applsci 14 07518 g001
Figure 1. Trend of muscle tension for the results of Bonferroni’s post-hoc tests (mean and 95%CI).
Figure 1. Trend of muscle tension for the results of Bonferroni’s post-hoc tests (mean and 95%CI).
Applsci 14 07518 g001
Table 1. Descriptive statistics for the gastrocnemius muscle.
Table 1. Descriptive statistics for the gastrocnemius muscle.
MuscleSpeedBody Weight Relief
100%75%50%25%
Mean ± SD
(95%) CI		Mean ± SD
(95%) CI		Mean ± SD
(95%) CI		Mean ± SD
(95%) CI
Gastrocnemius6 km11.3 ± 1.50
(10.6–12.0)		10.0 ± 1.36
(9.41–10.7)		9.34 ± 1.14
(8.80–9.87)		8.98 ± 1.53
(8.27–9.70)
10 km16.7 ± 2.73
(15.5–18.0)		14.8 ± 1.62
(14.0–15.5)		13.4 ± 1.02
(13.0–13.9)		12.7 ± 1.80
(11.9–13.6)
14 km22.6 ± 3.41
(20.95–24.15)		19.1 ± 2.82
(17.79–20.43)		17.6 ± 2.09
(16.60–18.56)		16.0 ± 1.85
(15.13–16.86)
18 km28.5 ± 3.37
(26.9–30.1)		24.9 ± 3.40
(23.3–26.5)		22.0 ± 3.32
(20.5–23.6)		19.9 ± 2.67
(18.7–21.2)
Table 2. Descriptive statistics for the tibialis anterior muscle.
Table 2. Descriptive statistics for the tibialis anterior muscle.
MuscleSpeedBody Weight Relief
100%75%50%25%
Mean ± SD
(95%) CI		Mean ± SD
(95%) CI		Mean ± SD
(95%) CI		Mean ± SD
(95%) CI
Tibialis anterior6 km11.9 ± 1.65
(11.1–12.6)		10.4 ± 1.57
(9.67–11.1)		9.58 ± 1.62
(8.82–10.3)		9.25 ± 1.54
(8.52–9.97)
10 km18.4 ± 2.68
(17.2–19.7)		15.9 ± 2.31
(14.8–17.0)		14.1 ± 2.10
(13.1–15.1)		12.6 ± 2.04
(11.6–13.5)
14 km23.7 ± 2.44
(22.6–24.8)		20.5 ± 2.50
(19.3–21.6)		17.9 ± 2.04
(17.0–18.9)		16.1 ± 1.81
(15.2–16.9)
18 km29.5. ± 2.63
(28.3–30.7)		25.6 ± 2.94
(24.2–27.0)		22.7 ± 2.45
(21.5–23.8)		20.2 ± 2.27
(19.1–21.2)
Table 3. Descriptive statistics for the rectus femoris muscle.
Table 3. Descriptive statistics for the rectus femoris muscle.
MuscleSpeedBody Weight Relief
100%75%50%25%
Mean ± SD
(95%) CI		Mean ± SD
(95%) CI		Mean ± SD
(95%) CI		Mean ± SD
(95%) CI
Rectus Femoris6 km7.91 ± 2.30
(6.84–8.99)		8.24 ± 1.74
(7.43–9.05)		7.20 ± 1.65
(6.43–7.97)		6.49 ± 1.35
(5.86–7.12)
10 km14.5 ± 3.92
(12.7–16.4)		12.1 ± 2.59
(10.9–13.3)		10.6 ± 1.91
(9.71–11.5)		8.96 ± 1.71
(8.16–9.76)
14 km21.0 ± 5.21
(18.6–23.5)		16.5 ± 3.09
(15.1–18.0)		13.7 ± 2.42
(12.6–14.8)		11.3 ± 2.06
(10.4–12.3)
18 km28.4 ± 6.48
(25.4–31.4)		20.1 ± 3.28
(18.5–21.6)		17.3 ± 2.34
(16.2–18.4)		14.5 ± 2.46
(13.3–15.6)
Table 4. Descriptive statistics for the biceps femoris muscle.
Table 4. Descriptive statistics for the biceps femoris muscle.
MuscleSpeedBody Weight Relief
100%75%50%25%
Mean ± SD
(95%) CI		Mean ± SD
(95%) CI		Mean ± SD
(95%) CI		Mean ± SD
(95%) CI
Biceps Femoris6 km8.86 ± 1.55
(8.14–9.59)		8.56 ± 1.47
(7.87–9.25)		8.30 ± 1.72
(7.50–9.10)		7.37 ± 1.59
(6.62–8.11)
10 km15.6 ± 1.80
(14.7–16.4)		13.7 ± 1.37
(13.1–14.4)		12.5 ± 1.36
(11.9–13.14)		10.7 ± 1.15
(10.1–11.2)
14 km21.8 ± 1.98
(20.8–22.7)		19.2 ± 2.28
(18.1–20.3)		16.6 ± 1.79
(15.8–17.4)		14.0 ± 1.92
(13.1–14.8)
18 km26.9 ± 3.15
(25.4–28.4)		24.5 ± 2.78
(23.1–25.8)		21.7 ± 1.91
(20.8–22.6)		18.4 ± 1.92
(17.5–19.3)
Table 5. Descriptive statistics for the gluteus maximus muscle.
Table 5. Descriptive statistics for the gluteus maximus muscle.
MuscleSpeedBody Weight Relief
100%75%50%25%
Mean ± SD
(95%) CI		Mean ± SD
(95%) CI		Mean ± SD
(95%) CI		Mean ± SD
(95%) CI
Gluteus maximus6 km7.97 ± 1.77
(7.14–8.79)		8.05 ± 1.54
(7.32–8.77)		7.59 ± 1.56
(6.86–8.32)		6.89 ± 1.69
(6.11–7.68)
10 km18.9 ± 4.88
(16.6–21.2)		15.5 ± 4.46
(13.4–17.6)		13.3 ± 3.46
(11.7–14.9)		11.3 ± 3.28
(9.76–12.8)
14 km25.4 ± 6.22
(22.5–28.3)		20.2 ± 5.32
(17.7–22.6)		17.7 ± 4.16
(15.7–19.6)		14.8 ± 3.93
(13.0–16.7)
18 km31.1 ± 7.78
(27.5–34.7)		25.5 ± 6.56
(22.4–28.5)		23.2 ± 6.03
(20.4–26.0)		19.5 ± 5.90
(16.7–22.2)
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Pietraszewski, P.; Gołaś, A.; Roczniok, R.; Gepfert, M.; Zając, A. EMG Activity of Lower Limb Muscles during Anti-Gravity Treadmill Running with Different Loads and Speeds. Appl. Sci. 2024, 14, 7518. https://doi.org/10.3390/app14177518

AMA Style

Pietraszewski P, Gołaś A, Roczniok R, Gepfert M, Zając A. EMG Activity of Lower Limb Muscles during Anti-Gravity Treadmill Running with Different Loads and Speeds. Applied Sciences. 2024; 14(17):7518. https://doi.org/10.3390/app14177518

Chicago/Turabian Style

Pietraszewski, Przemysław, Artur Gołaś, Robert Roczniok, Mariola Gepfert, and Adam Zając. 2024. "EMG Activity of Lower Limb Muscles during Anti-Gravity Treadmill Running with Different Loads and Speeds" Applied Sciences 14, no. 17: 7518. https://doi.org/10.3390/app14177518

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