Muscles, Volume 4, Issue 1 (March 2025) – 9 articles

Background/Aims: The pelvic floor muscles are important structures involved in pelvic floor tone, pelvic organ support, and continence. The aim of this study was to perform an update on the pelvic floor muscle structure and function alterations of women with pelvic floor dysfunctions. Methods: A systematic search was undertaken in two electronic databases, PubMed/Medline and Ovid Discovery to find manuscripts (in English), published between 1 January 2002 and 31 July 2022, including all clinical studies using the following search terms: “muscle” or “extracellular matrix *” and “pelvic floor dysfunction *”. All clinical trials, observational, or animal studies examining the muscle and reporting pelvic floor dysfunction as a primary outcome were included. Case reports, literature reviews, conference papers and theses, and unpublished data were excluded. To ensure that no eligible articles were overlooked, the reference lists of all included papers underwent manual scrutiny. The bias level was estimated using Newcastle–Ottawa Scale (NOS) for cohort and case-control studies. A qualitative synthesis was performed. Results: The significant qualitative and quantitative heterogeneity between the studies did not allow for a quantitative analysis. Of the 30 articles selected with a total of 5592 women, 15 referred to the analysis of structural muscle defects, which included 3365 participants with urinary incontinence, pelvic organ prolapse, fecal incontinence, cistocele, rectocele, and sexual dysfunction; 10 manuscripts referred to the study of pelvic floor muscle function with a population of 2042 women, such as urinary incontinence, pelvic organ prolapse, fecal incontinence, and sexual dysfunction; and 5 papers evaluated cellular and/or molecular changes affecting the pelvic floor muscles, like urinary incontinence, pelvic organ prolapse, and rectocele, which included a total of 185 participants. Women with pelvic floor muscle defects are at greater risk of pelvic floor dysfunctions, and inversely, women with pelvic floor dysfunctions have more pelvic floor muscle defects than women without pelvic floor dysfunctions. These patients demonstrate a reduction in muscle tone, contraction strength, and resistance, a compromised neuromuscular activity, and an alteration of the normal composition and organization of the muscle cells. Conclusions: Women with pelvic floor dysfunction have anatomical muscle defects, disturbance of muscle function and cellular changes involving muscle cells and nerve fibers. Full article

The assessment of joint ranges is an essential component of the physical examination, enabling monitoring and follow-up. Additionally, it is a key component of muscle mobility assessment. Smartphone applications for range-of-motion assessments offer a cost-effective alternative to traditional measurement tools, reducing the need for expensive equipment while maintaining accuracy. Their portability and ease of use provide significant advantages in clinical settings, allowing for quicker assessments. This, in turn, can enhance patient care by enabling more frequent monitoring and timely interventions, ultimately improving treatment outcomes. This study evaluated the validity and reliability of the PhysioMaster application in measuring knee range of motion. Twenty-nine participants performed passive knee extensions, with data collected simultaneously through the application and video recordings for posterior angle calculations. The application demonstrated excellent validity, with intraclass correlation (ICC = between 0.729 and 0.814) and the Pearson correlation values ranging from r = 0.908 to 0.974. For inter-rater reliability, ICC was 0.898 and Pearson correlation coefficient r = 0.82. Additionally, the coefficient of variation was 5.18%, and the measurement error was 0.82°. The results showed that the PhysioMaster application is a valid and reliable tool for assessing passive knee extension in clinical environments, supporting efficient and accurate patient evaluations. Full article

Barbell (BB) and dumbbell (DB) devices are commonly used during a bench press to develop the muscles of the chest, shoulders, and upper arms. Recently, a complete upper body bar (CUBB) was designed to train the muscles of the forearm by allowing for pronation and supination while providing the same traditional training for the rest of the upper body. The purpose of this study was to investigate the effectiveness of the CUBB relating to the EMG activity of the forearm during a bench press. Methods: A total of 21 healthy college-aged men volunteered for this study. EMG sensors were placed on the anterior deltoid (AD), pectoralis major (PEC), triceps brachii (TRI), pronator teres (PRO), and supinator (SUP). The participants went through a bench press test in a series of three different randomized conditions: the DB, the BB, and the CUBB. Resistance was set at 30% of body weight. A repeated-measures ANOVA was used to analyze the normalized EMG data (alpha = 0.05). Results: For the forearm muscles, the CUBB exhibited 41% and 37% higher PRO activation than the DB and BB, respectively. In addition, the CUBB exhibited 67% and 30% more SUP activation than the BB and DB, respectively. For the shoulder and chest muscles (AD and PEC), no significant differences were found among the three conditions. Conclusions: Bench pressing with a CUBB can engage more upper body muscles and offer individuals additional training benefits. Full article

Elevated temperatures have been shown to decrease muscle force production, with potential causes including protein unfolding, enzyme denaturation, and reactive oxygen species (ROS). This study aimed to investigate whether fucoidan, a compound derived from brown seaweed, could mitigate heat-stress-induced loss of muscle function. C57BL/6 mice were orally administered fucoidan (400 mg/kg/day) from one of two different seaweed species Fucus vesiculosus (FVF) or Undaria pinnatifida (UPF) or vehicle control for seven consecutive days. Subsequently, the in vitro muscle function of the fast-twitch extensor digitorum longus (EDL) was assessed at either 25 °C (control) or 43 °C (heat stress). Functional analysis was complemented with gene analysis and the C2C12 myoblast heat-stress assay. The temperature (43 °C)-induced loss of force produced by the EDL muscle was significantly attenuated by fucoidan from FVF but not UPF. Fucoidan from UPF did not affect gene expression levels, whereas fucoidan from FVF significantly increased the expression levels of HSP90. In mouse C2C12 myoblasts, heat stress induced a significant increase in ROS production which was significantly reduced by both fucoidan species. These results suggest fucoidan extracted from Fucus vesiculosus may be an effective preventive strategy to protect against heat-induced loss of muscle strength in fast-twitch muscles. Full article

Background: Algometry is a validated and reliable measurement tool, but there are still no reliable data for the different algometers used by different raters in the same participant. Objective: The aim of this study was to determine the intra-reliability of pressure pain thresholds (PPTs) measured using a digital algometer with and without a digital screen by different raters at the same time in a pain-free population. Methods: Participants were healthy adults. PPTs were assessed using two different algometers: a digital algometer with a digital screen for a feedback of the pressure curve rate (SpTech Digital Algometer); and a digital algometer without a screen (Wagner Instruments FDX-25, Greenwich, CT, USA). Four PPT points were used: upper trapezius, lumbar spine, extensor carpi ulnaris, and tibialis anterior. The Copenhagen Psychosocial Questionnaire II was used to assess burnout, stress, sleeping problems, depressive symptoms, somatic stress, and cognitive stress. The intraclass coefficients (ICCs) for intra-rater reliability was calculated using a two-way mixed effects model, single measurement type, and absolute agreement definition. Results: A total of 47 healthy participants with a mean age of 30.51 (11.35) years were included. The upper trapezius and extensor carpi ulnaris had the lowest PPT values, and the tibialis anterior had the highest PPT value. Females had the lowest PPT values when compared with males with p < 0.05 in the upper trapezius and extensor carpi ulnaris regions. The intra-rater reliability ranged from good to excellent reliability, with the ICC values of rater 1 being higher when compared with rater 2. The PPT in tibialis anterior had the highest mean ICC scores. Conclusions: The intra-rater reliability of PPTs measured by different digital algometers ranged from good to excellent reliability. The rater with more experience demonstrated higher reliability. Full article

A history of bronchiolitis may lead to changes in health-related physical fitness in children and adolescents. The aim of this study was to analyze the influence of history of bronchiolitis on health-related physical fitness components (muscle strength and cardiorespiratory fitness) in children and adolescents. A cross-sectional study was conducted, and 86 participants (aged 7–14 years; all males) were divided into two groups: a group with (n = 40) and without (n = 46) history of bronchiolitis. Muscle strength was assessed with handgrip and isometric quadriceps strength tests with handheld dynamometers and the five-times sit-to-stand test. Cardiorespiratory fitness was assessed with the six-minute walk test (6MWT). The Mann–Whitney test was used to compare the health-related physical fitness tests between groups and the binary logistic regression model was used to estimate the potential risk or protective factors in participants. No significant differences were observed between the groups in muscle strength tests. Participants without bronchiolitis walked a greater distance in the 6MWT than those with bronchiolitis (p = 0.002), and this appears to reproduce a protective factor in the group without bronchiolitis with an odds ratio of 0.99 [95% confidence interval: 0.98–0.99]. In this study, a history of bronchiolitis appears to influence cardiorespiratory fitness, but not muscle strength, in children and adolescents. Full article

This study examined the association between knee proprioception, strength, and functional symmetry in healthy individuals using isokinetic strength tests, proprioception assessments, and hop tests. Twenty young, healthy adults (mean age 26.5 ± 4.1 years, 85% right-limb dominant) participated. Knee extensor and flexor strength were measured at 60°·s⁻¹ and 240°·s⁻¹. Proprioception was assessed by measuring passive joint position sense (JPS1: position recognition; JPS2: repositioning) and kinesthesia (threshold to detection of passive motion, TTDPM). Functional performance was evaluated using the single-leg hop test (SLH), triple-hop test (TH), and crossover hop test (COH). Symmetry was calculated using the limb symmetry index (LSI) as the ratio of non-dominant to dominant limb values. The results showed that THT (p = 0.011) and COH (p = 0.032) performance was superior on the dominant limb. A correlation analysis revealed strong positive correlations between hop test distances and knee extensor strength (r = 0.56–0.70, p < 0.001). JPS symmetry was negatively correlated with hop test symmetry (JPS1: SLH, r = −0.53; THT, r = −0.49; COH, r = −0.70). The participants with poorer position sense on the non-dominant leg were 2.7 times more likely to show LSI < 90% (p = 0.035). In conclusion, proprioception—particularly joint position sense—is associated with functional symmetry during dynamic tasks, highlighting the importance of proprioceptive assessments in rehabilitation and injury prevention. Full article

Background/Objectives: CrossFit^® is one of the most popular yet controversial training regimens. Some groups extol the positive effects of its practice, while others argue that it is unsafe and that there is limited information. The aim of this study was to investigate, through a self-reported questionnaire, the epidemiology of Portuguese CrossFit^® training practitioners. Methods: Statistical analyses, including Mann–Whitney U, chi-square, Spearman’s rho correlations, and logistic regressions, were conducted. Results: A total of 288 practitioners completed the questionnaire, with 39.9% reporting injuries. These injuries occurred mainly during training, particularly when performing gymnastics exercises. Tendon (40.9%) and shoulder (46.1%) were the most common injuries. Key risk factors for injury included male gender (OR = 2.7), years of practice (4–6 years: OR = 7.22), heavier body weight (OR = 4.76), and higher weekly training volume (4–6 times per week). Conclusions: Approximately 40% of CrossFit^® practitioners are expected to experience injuries, particularly in the shoulder and tendons. Injury risk is influenced by factors such as practice years, weekly training, sex, and body weight. These findings may help guide practitioners, coaches, and health professionals in better understanding the risk factors, mitigating injuries, and developing effective injury prevention strategies. Full article

Friedreich’s ataxia (FRDA) results from a faulty mitochondrial protein known as Frataxin. The purpose of this case report was to test whether skeletal muscle in FRDA can adapt to an endurance-based training program using neuromuscular electrical stimulation (NMES). A 36-year-old female with FRDA completed twelve training sessions, each lasting 30 min over 30 days, focused on the forearm muscles using NMES. Pre- and post-training session measurements of contractions, muscle-specific endurance, and muscle mitochondrial capacity were taken per training session. Training contractions increased from 4200 to 9420. Muscle-specific endurance increased by 14% at 2 Hz and 17% at 4 Hz. Muscle endurance at 6 Hz increased from 0% to 51%. The rate constant of mitochondrial capacity was 0.95 min⁻¹ pre- and 0.99 min⁻¹ post-training session. In conclusion, one month of NMES increased training volume and muscle-specific endurance but did not change mitochondrial capacity. Muscle adaptations to endurance training were seen in FRDA, but increased training might be needed to test if mitochondrial capacity can improve. Full article