Muscles

This work investigates the macroscopic behavior of skeletal muscles from a system-theoretic perspective. Based on data available in the literature, we propose an initial evaluation model for isometric force generation, i.e., force produced at a constant muscle length or in quasi-static conditions, as a function of muscle length and neuronal excitation frequency. This model enables a more physics-inspired representation of isometric force by employing a nonlinear spring framework with controllable properties such as stiffness and rest length. Finally, we introduce a hybrid dynamical filter model to describe components of the sensory system responsible for relaying information about muscle length and its rate of change back to the Central Nervous System. As an application case, we present the modeling of the oculomotor system, highlighting the relevance of the proposed modeling approach in a physiologically meaningful control task. Full article

Background: The reliable assessment of cervical muscle morphology is essential for both clinical and research use. However, evidence on the reliability of ultrasound measurements remains limited. Objective: To investigate the intra-rater and test–retest reliability of morphological measurements of the Longus Colli, Sternocleidomastoid, Multifidus Cervicis, and Semispinalis Capitis muscles using musculoskeletal ultrasound. Methods: Cross-sectional area, anteroposterior, and lateral dimensions were assessed using B-mode ultrasound. Anterior neck muscles were scanned in the supine position, while posterior neck muscles were scanned in the prone position. Each muscle was measured three times (to assess intra-rater reliability), which was repeated after 30 min (to assess test–retest reliability). Measurements were also normalized according to BMI and neck circumference. Results: Intra-rater reliability was found to be good to excellent for the Longus Colli (ICC = 0.77–0.92), excellent for the Sternocleidomastoid (ICC = 0.93–0.99), good to excellent for the Semispinalis Capitis (ICC = 0.89–0.97), and moderate to excellent for the Multifidus Cervicis (ICC = 0.69–0.92). Test–retest reliability was found to be moderate to good for the Longus Colli (ICC = 0.73–0.87), good to excellent for the Sternocleidomastoid (ICC = 0.84–0.98), good to excellent for the Semispinalis Capitis (ICC = 0.78–0.95), and good to excellent for the Multifidus Cervicis (ICC = 0.80–0.92). Conclusions: Musculoskeletal ultrasound demonstrates strong reliability for cervical muscle assessment, supporting its clinical use. Full article

Chronic musculoskeletal pain negatively affects patients’ quality of life, and pain perceptions may significantly influence rehabilitation outcomes. This study investigated the relationships among pain intensity, pain perceptions, and kinesiophobia in individuals with chronic musculoskeletal pain. No previous studies have examined these variables in combination. A cross-sectional observational study was conducted with 37 participants with non-specific chronic musculoskeletal pain for at least 6 months, affecting the neck (n = 8), lower back (n = 18), upper limbs (n = 5), lower limbs (n = 5), or shoulder (n = 1). The following validated tools were used: (a) Pain Beliefs and Perceptions Inventory (PBPI), (b) the Tampa Scale for Kinesiophobia (TSK), and (c) the Short-Form McGill Pain Questionnaire (SF-MPQ). Spearman r correlation analyses were performed. Total kinesiophobia scores were positively correlated with (a) total pain intensity (McGill score) (r = 0.37, p = 0.022), (b) present pain intensity (PPI) (r = 0.52, p = 0.001), (c) pain duration (r = 0.51, p = 0.001), (d) the “mystery” factor of pain perception (r = 0.41, p = 0.013), and (e) the Visual Analogue Scale (VAS) (r = 0.42, p = 0.009). The total pain perception scores were positively associated with the “fear of injury” factor of kinesiophobia (r = 0.36, p = 0.028). The McGill pain scores were strongly correlated with both PPI (r = 0.63, p = 0.001) and VAS (r = 0.51, p = 0.001). There is a significant relationship between pain perception and kinesiophobia levels in patients with chronic musculoskeletal pain. Limitations of the study include a small and heterogeneous sample regarding pain localization. Further research is required using larger, more homogeneous populations to confirm the present findings. Full article

Skeletal muscle aging and related diseases are characterized by progressive loss of muscle mass, strength, and metabolic function. Central to these processes is mitochondrial dysfunction, which impairs energy metabolism, redox homeostasis, and proteostasis. In addition, non-mitochondrial factors such as muscle stem cell exhaustion, neuromuscular junction remodeling, and chronic inflammation also contribute significantly to muscle degeneration. This review integrates recent advances in understanding mitochondrial and non-mitochondrial mechanisms underlying muscle aging and disease. Additionally, we discuss emerging therapeutic approaches targeting these pathways to preserve muscle health and promote healthy aging. Full article

Limb–girdle muscular dystrophy (LGMD) encompasses a heterogeneous group disease, genetic and phenotypically. There are more than 30 subtypes divided into two groups: autosomal dominant and recessive. LGMDs are characterised by muscle weakness; however, psychosocial factors seem to be affected too, such as HRQoL. Given the lack of literature in this respect, the present cross-sectional study aimed to create a patient profile comparing both dominant and recessive forms by analysing HRQoL through the INQoL, and sociodemographic data. The LGMD-recessive group had a worse HRQoL compared to the dominant group, specifically in the dimensions of muscle weakness (p = 0.007), emotion (p = 0.046), independence (p = 0.029), and body image (p = 0.022). In addition, in the LGMD-dominant group, 77.9% of the relational indicator was explained by age (B = 0.907, p = 0.012), which can be understood as a limitation in their social role due to the disease progression. In contrast, no sociodemographic variables were found to be predictive of the HRQoL of patients with recessive forms of LGMD. These results are relevant for clinical practice, as they reflect the most affected areas of HRQoL in LGMD patients, differentiating between recessive and dominant forms. Full article

Ergogenic supplements are becoming increasingly popular in the diet of trained individuals, due to their potential benefits. Ashwagandha (Withania somnifera) is one of the supplements that has recently grown in popularity. Despite growing interest, its scientific background remains limited and sometimes inconsistent. Objective: This overview of systematic reviews aimed to evaluate the effects of Ashwagandha supplementation on sports performance and health-related outcomes. Methods: A systematic literature search was carried out on the following electronic databases: PUBMed, Scopus, Academic Search Complete, SPORTDiscus, Web of Science, and Google Scholar, using the search terms “ashwagandha” and “systematic review” in the title or abstract of the publication in July 2024. The eligibility of the articles was assessed using the PICOS (Population, Intervention, Comparator, Outcomes, and Study Design) approach, and risk of bias was assessed using the AMSTAR-2 checklist. Results: Of the 2388 systematic reviews found, 11 met the inclusion criteria, which included 151 original studies representing 9005 individuals. Findings suggest that Ashwagandha supplementation may improve various aspects of sports performance, such as endurance and muscular strength, as well as health-related outcomes, including anxiety reduction, improved sleep quality, and enhanced sexual function. The most commonly used doses of Ashwagandha supplementation are between 500 mg and 1000 mg a day. Conclusion: While current evidence indicates promising effects of Ashwagandha on physical and psychological parameters, further high-quality randomized controlled trials are needed. Therefore, its use in athletes or healthy individuals should be considered with caution and based on individual needs. Full article

Background: Expression of maximal and rapid force in the hip, knee, and plantar flexors is important for athletic performance in female soccer. This study was designed to determine the effect of relative isometric strength in the isometric mid-thigh pull (IMTP) on countermovement jump (CMJ) and rebound jump (CMJ-R) performance in female youth soccer players. Methods: Ninety-six female soccer players (age: 14.1 ± 2.3 years, height: 160.5 ± 9.7 cm, mass: 55.0 ± 10.3 kg) completed three trials of the IMTP, CMJ, and CMJ-R using force plates. Players were categorized as stronger (top quartile, n = 19) and weaker players (bottom quartile, n = 23) based on IMTP relative net peak force. One-way Bayesian independent t-tests were performed between stronger and weaker players. Results: Very large difference in lower limb strength between groups (g = 5.05). Moderate to very strong evidence to support that stronger players had greater countermovement depth and time to take-off with similar jump heights than weaker players. Strong evidence was observed for CMJ-R height, with stronger players falling from a greater height and executing similar ground contact times compared to weaker players. Conclusions: Relative strength has implications for CMJ-R, highlighting the importance of developing relative strength in hip, knee, and plantar extensors. Full article

Amyotrophic lateral sclerosis (ALS) is a progressive disease that degeneratively damages both upper and lower motor neurons, eventually resulting in muscular paralysis and death. Although ALS is broad in scope and commonly thought of as a motor neuron disease, more active research sheds light on the that role skeletal muscle plays in the development and progression of the disease. Muscle tissue in ALS patients and in animal models demonstrates severe regenerative deficits, including impaired myogenesis and impaired myoblast fusion. In ALS, muscle stem cells, known as satellite cells, show poor performance in activation, proliferation, and differentiation and thus contribute to ALS muscle wasting. Moreover, the pathological tissue environment that inhibits myoblast fusion is made up of proinflammatory cytokines, oxidative stress, and a lack of trophic signals from the neuromuscular junction, which greatly disrupts homeostatic regulation. It is likely that skeletal muscle is instead a dynamic player, fueling neuromuscular degeneration as opposed to a passive responder to denervation. One must appreciate the cellular and molecular changes that complicate muscle regeneration in ALS for effective treatment to be developed, permitting simultaneous interventions with both muscle and neurons. Full article

Service-Learning (SL) is an innovative educational methodology that integrates academic learning with active community engagement, fostering both technical and transversal competencies. This pilot study explores the implementation of an SL-based experience within the Physiotherapy Degree at the University of Extremadura. The primary objective was to design and deliver therapeutic exercise programs targeting patients with cardiorespiratory conditions, utilizing local community resources. A total of 44 third-year physiotherapy students participated in the design and simulated the implementation of community-based interventions targeting muscular strength, postural control, balance, and endurance. A mixed-methods approach was used, combining descriptive statistics (SPSS v23) and thematic analysis of student reflections to assess the impact of SL on the development of specific professional competencies, including clinical reasoning, patient communication, therapeutic planning, and adaptation of interventions to diverse environments. The results show a significant improvement in students’ theoretical and practical understanding, with over 70% of participants rating their learning experience between 8 and 10 (on a 0–10 scale) in aspects such as pathology description, clinical assessment, and exercise planning. Additionally, 92% reported improved teamwork, 89% noted better adaptability, and 87% reported enhanced decision-making skills. The findings suggest that SL can enhance perceived learning in musculoskeletal rehabilitation and support the transition from academic training to clinical practice. However, the study is exploratory and based on perceived outcomes, and future research should include validated tools and real patients to assess its impact more rigorously. This pilot study highlights the value of integrating musculoskeletal-focused training—targeting strength, balance, and endurance—into physiotherapy education through Service-Learning methodology. The study highlights SL’s potential to enrich physiotherapy education while leveraging community spaces—such as those in Extremadura, a region with three UNESCO World Heritage Sites—as dynamic learning environments. Full article

This study aimed to describe and compare the serratus anterior (SA) and latissimus dorsi (LD) muscle activity during six hypopressive exercise (HE) positions performed in open and closed kinetic chains. While previous studies analyzed abdominal and pelvic muscle activity during HE, research on scapular stabilizers like SA and LD remains underreported. Twenty-five healthy adults (mean age, 42.9 ± 8.4 years; BMI, 22.1 ± 2.4 kg/m²) with prior HE experience performed three open and three closed-chain HE positions. Surface electromyography recorded bilateral SA and LD activity, normalized to maximum voluntary isometric contraction (MVIC). SA showed greater activation than LD across all positions, with moderate activation levels (20–40% MVIC), while LD activation remained mild (<20% MVIC). Significant differences were found across positions and kinetic chain conditions. SA activation was higher during closed-chain standing (W = 41; p < 0.001; r = −0.74) and kneeling (W = 9; p < 0.001; r = −0.94), while LD activity increased significantly in the seated closed-chain position (left LD: W = 26; p < 0.001; r = −0.84; right LD: W = 20; p < 0.001; r = −0.87). These findings suggest body and kinetic chain positioning influence scapular muscle recruitment during HE. Further research is warranted to determine clinical applications. Full article

Blood flow restriction exercise (BFRE), which partially restricts arterial inflow and occludes venous outflow to the limbs, has gained attention for its potential to elevate serum brain-derived neurotrophic factor (BDNF), a key mediator in the muscle–brain crosstalk leading to improvement of neuroplasticity, neurogenesis, and cognitive health. In this systematic review of five studies, participants included healthy young adults, older adults, and individuals with clinical conditions. Most investigations found that BFRE increased serum BDNF, with responses comparable to those elicited by high-intensity exercise. Proposed mechanisms center on the metabolic demands of BFRE, which may increase lactate and thereby trigger BDNF release. However, two studies showed no significant changes, possibly due to short exercise duration, insufficient training intensity, or age-related reductions in BDNF responsiveness. The small sample sizes and varied protocols across studies limit definitive conclusions. Nonetheless, BFRE may provide a valuable alternative for populations who cannot tolerate high mechanical loads, and it shows promise for enhancing neurotrophic support and potentially improving brain health. Larger, well-controlled trials are warranted to refine BFRE protocols and better understand optimal strategies for increasing BDNF and supporting neuroplasticity. Full article

Boxing is a sport that has a high level of oxygen use within the Rectus Femoris muscle, with recovery between rounds important to subsequent performance. The study aimed to determine muscle oxygen use in male and female professional boxers in response to a repeated sprint stimulus. 10 male (age: 26 ± 5 years, height: 177 ± 4 cm, weight: 72 ± 6 kg) and 6 female (age: 29 ± 4 years, height: 173 ± 2 cm, weight: 73 ± 4 kg) professional boxers took part. Participants attended a single session where a Moxy near-infrared monitor was placed on the rectus femoris muscle of both legs. Participants completed 2 × 30 s Wingate-based sprint efforts with a 60 s active recovery (maintaining 60 rpm against 50 W resistance). Skeletal muscle oxygenation was recorded throughout. Significant differences were found in peak power, average speed and rate of fast desaturation between males and females (p < 0.001) in both sprints. There was a significant difference in males and females for the rate (sprint 1M: −5.6 ± 1.2%.s⁻¹, 1F: −2.3 ± 1.9%.s⁻¹, p < 0.05; sprint 2M: −4.2 ± 1.1%.s⁻¹, 2F: −1.5 ± 0.9%.s⁻¹, p < 0.05) and duration of fast desaturation (sprint 1M: 6.1 ± 1.3 s, 1F: 3.7 ± 2.8 s, p < 0.05; sprint 2M: 7.3 ± 1.6 s, 2F: 4.5 ± 1.0 s, p < 0.05) in both sprints. This study demonstrates that male professional boxers have a significantly different oxygen use and recovery in response to a high-intensity stimulus compared to female boxers. In both male and female boxers, the ability to perform subsequent high-intensity activity is dependent on the quality of the recovery from the initial high intensity activity. Therefore, there is a greater need to focus training to improve recovery kinetics in boxing. Full article

Background: Previous work has found that combining plyometric and resistance training in a single session can be effective in improving maximum strength (muscle contraction ability), vertical jumping, and sprint acceleration performance in young soccer players. However, the literature is scarce in relation to young rugby union players. Thus, the purposes of the present study were to examine the effects of a 6-week combined training (CT) programme that combined plyometric and resistance training in the same session on physical performance measures in adolescent male rugby union players and whether a 4-week period of plyometric training exclusion (Detraining) affects training adaptations. Methods: The participants (n = 15) completed a 6-week CT intervention and 4 weeks of plyometric detraining during the schoolboy rugby union in-season. A performance testing battery was conducted pre-intervention, post-intervention, and 4 weeks post-intervention. Results: A repeated measures ANOVA showed a significant effect for time on CMJ variables (mean power, mean force, and modified reactive strength index [RSI]), 3RM back squat strength, and 505 test time (p < 0.05). Pairwise comparisons revealed that CMJ variables (mean force, mean power, and peak power), 3RM back squat strength, and 505 test performance significantly increased from pre-intervention to post-intervention (p < 0.05). The 4-week plyometric detraining period significantly augmented CMJ variables (mean force, mean power, and modified RSI) and performance measures (standing broad jump [SBJ], 20 m sprint time, 505 test, and 3RM strength). Conclusions: The findings indicate that a 6-week CT programme can augment measures of lower-body power, maximal strength, and change of direction performance in adolescent male rugby union players, and a 4-week resistance training-only period (plyometric detraining) does not negatively affect performance adaptations. Full article

This study examined the impact of different breath-holding conditions on iliopsoas and other hip flexor muscle activity in individuals with chronic ankle instability (CAI). It has been hypothesised that impaired diaphragmatic function influences iliopsoas activation, potentially contributing to motor control deficits in patients with CAI. Eleven adults with a history of chronic ankle sprain participated in this study. Maximal isometric hip flexion was assessed under three breath-holding conditions: end-expiration, end-inspiration, and the intermediate state. Surface electromyography was used to record the muscle activity of the iliopsoas, rectus femoris, sartorius, and tensor fasciae latae, while the peak hip flexion torque was measured using an isokinetic dynamometer. Under the end-inspiration condition, iliopsoas activity on the affected side was significantly lower than that on the control side (p < 0.05). However, no significant differences were observed between the affected and control sides in the activity of the other hip flexor muscles or the peak hip flexion torque across breath-holding conditions. This study highlights the association between reduced iliopsoas activity during end-inspiration and compromised diaphragmatic function in patients with CAI. Future research should explore dynamic movement tasks and larger sample sizes to elucidate neuromuscular mechanisms further and refine rehabilitation strategies. Full article

This systematic review aims to evaluate the impact of hormonal fluctuations during the menstrual cycle on the performance of female athletes. Methods: Following PRISMA guidelines, a comprehensive search was conducted in Scopus, Web of Science, and PubMed databases using the keywords: (“Menstrual cycle”) AND (“performance” OR “female athlete” OR “sport” AND NOT “male”); AND NOT (“contraceptive”). Inclusion criteria focused on original studies published between 2013 and 2023, in English or Spanish, involving eumenorrheic female athletes without menstrual disorders or oral contraceptive use. The studies were critically assessed using the McMaster scientific review method. Results: Thirteen eligible articles were reviewed, comprising a total sample of 152 athletes. Significant findings include increased flexibility during the ovulatory phase and enhanced aerobic and anaerobic capacities in the luteal phase. Additionally, the menstrual and premenstrual phases notably influenced aerobic and anaerobic capacities, performance perception, symptomatology, and exercise-induced muscle damage. Conclusion: Hormonal fluctuations can impact female athletes’ performance. However, further research is warranted due to inconsistent results stemming from variations in cycle phases studied, lack of standardized methodologies, small sample sizes, and short observation periods. Full article

The strength and conditioning literature examining neuromuscular physiology, bioenergetics, neuroendocrine factors, nutrition and metabolic factors, and the use of ergogenic aids, as well as physical and physiological responses and adaptations, have clearly identified the benefits of participating in regular resistance training programs for athletic populations, especially as it relates to improving muscular strength. Beyond evidence-based research, models for resistance training program implementation are of considerable value for optimizing athletic performance. In fact, several have been provided that address general to specific characteristics of athleticism (i.e., strength endurance, muscular strength, and muscular power) through resistance training over the decades. For instance, a published model known as the strength–endurance continuum that enhances dynamic correspondence (i.e., training specificity) in athletic populations by developing structural, metabolic, and neural capacities across a high-load, low-repetition and low-load, high-repetition range. Further models have been developed to enhance performance approaches (i.e., optimum performance training model) and outcomes (i.e., performance pyramid), even within specific populations, such as youth (i.e., youth physical development model). The ten, five, three, or 10-5-3 (TFT) model for strength and conditioning professionals synthesizes currently available information and provides a framework for the effective implementation of resistance training approaches to suit the needs of athletes at each stage of development. The model includes three key components to consider when designing strength and conditioning programs, denoted by the acronym TFT (ten, five, three). Over recent years, the model has gained much support from teams, coaches, and athletes, mainly due to the ability to streamline common knowledge within the field into an efficient and effective resistance training system. Furthermore, this model is distinctly unique from others as it prioritizes the development of strength–endurance, muscular strength, and muscular power concurrently. This paper explains the model itself and begins to provide recommendations for those interested in implementing TFT-based approaches, including a summary of points as a brief take-home guide to implementing TFT interventions. It is the author’s hope that this paper encourages other performance professionals to share their models to appreciate human ingenuity and advance our understanding of individualized approaches and systems towards the physical development of the modern-day athlete. Full article

Benign paroxysmal torticollis (BPT) is a condition characterized by episodes of alternating head tilt in infants. Mild cases may be mistaken for Congenital Muscular Torticollis, potentially leading to unnecessary treatment. This case report describes an infant with suspected mild BPT who exhibited alternating head tilt and colic but demonstrated normal motor development. The head tilt resolved spontaneously without intervention. Physical therapists should be aware of mild benign paroxysmal torticollis and monitor such cases carefully to differentiate it from other forms of torticollis and to provide reassurance to parents. Full article

Hip injuries are common in contact sports, particularly in high-impact activities. A well-known type of hip trauma is the hip pointer, which is a contusion of the iliac crest caused by a direct blow. Typically, hip pointers involve the lateral aspect of the iliac crest. In this case report, we present an unusual variation of this injury affecting the posterior iliac crest near the posterior superior iliac spine (PSIS). We describe two cases of elite athletes who sustained posterior iliac crest trauma, a condition we propose naming the “posterior hip pointer”. This report highlights the clinical presentation, imaging findings, treatment approach, and implications for sports medicine. Full article

Improving and maintaining an ideal body composition is important for sporting achievement and good health. Body composition assessment is therefore a tool used to monitor training and to evaluate the objectives of a training plan for health purposes. Ultrasound (US) emerges as an alternative to evaluate the thickness of subcutaneous cellular tissue, as well as muscle thickness: (1) Background: We aim to evaluate and compare the anthropometric and ultrasound measurements used to quantify the effects of strength training. (2) Methods: A total of 31 students (22.3 ± 4.14 years of age), 25 men and 6 women, from the Professional Programme in Sport were enrolled in the Physical Preparation course at the Institución Universitaria Politécnico Colombiano Jaime Isaza Cadavid. Protocol: Pre- and post-intervention ultrasound and anthropometric evaluations of a strength training programme with a predominance of the eccentric component were performed three times a week for 4 weeks. For the pre- and post-intervention relationship of the quantitative anthropometric and ultrasound variables, the Wilcoxon signed-rank test was used; the effect size of a Wilcoxon test was also calculated using the rank correlation, and the correlation of the anthropometric and ultrasound variables was determined using Spearman’s correlation coefficient, with a p-value < 0.05 considered statistically significant. (3) Results: There were no statistically significant differences in the anthropometric variables assessed, but there were significant differences in measures of quadricep muscle size and in the control parameter echo-intensity (EI) of subcutaneous fat in the variables. (4) Conclusions: The US of the quadriceps can measure changes in muscle thickness even without changes in muscle mass assessed by anthropometry, making it an excellent tool for the evaluation and monitoring of strength training. Full article