Muscles

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

Non-contact injuries are common in collegiate throwing athletes. Identifying musculoskeletal issues that predispose athletes to injuries would be valuable for reducing the associated risk. The purpose of this pilot study was to use binomial logistic regression to identify injury-prone athletes with multiple pre-season functional measures and demographic information. Eighteen Division II baseball and softball athletes underwent pre-season functional testing including measures of manual muscle testing of the dominant shoulder muscles (MMT), the functional movement screen (FMS), and closed kinetic chain upper extremity stability (CKCUES). A certified athletic trainer at the university diagnosed and documented the injuries that these athletes sustained over the course of the season. Binomial logistic regression models were used to assess the effects of FMS composite score, CKCUES normative score, MMT scores, and demographic information on the likelihood that participants would sustain (a) any type of injury and (b) a shoulder injury during the competitive season. The model for injury was not significant (p = 0.822), correctly classifying 72.2% of cases. The model for shoulder injury was significant (p = 0.039) and correctly classified 100% of cases. These results suggest that shoulder injury incidence may potentially be predicted using sport-specific movement tests in baseball and softball athletes. A larger sample size is needed to verify these results in the future. Full article

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

Background: Surface mechanomyographic (sMMG) signals have been used to examine sex-specific differences in the mechanical behavior of muscle during fatiguing exercise. However, studies often utilize simple amplitude- and frequency-based analyses, which only reveal the static components of the sMMG signal. Methods: Thus, a wavelet-based analysis was used to examine changes in the spectral intensity of the non-dominant limb’s vastus lateralis during a fatiguing, maximal, unilateral isometric leg extension in recreationally active men (n = 11) and women (n = 10). Relative changes in spectral intensities and instantaneous mean frequency (IMF) were examined using linear mixed-effect models. Time-to-task failure was compared using an independent sample t-test. Results: The neuromuscular responses demonstrated parallel decreases in IMF (p < 0.001). Further, there were parallel, nonlinear, decreases in spectral intensity across wavelets (p < 0.001) and there were no sex differences in time-to-task failure (p = 0.15). Conclusions: These data showed no sex-specific differences in exercise fatigability or muscle mechanics during fatiguing exercise of the leg extensors. However, when collapsed across sex, wavelet-specific changes in spectral intensity over time reveal novel insights into the interplay between low- and high-frequency components during fatigue. Full article

Maximal eccentric (MES) and isometric (MIS) muscle strength may enhance vertical jump performance by facilitating preloading and reducing energy loss during the eccentric (ECC) phase of the stretch-shortening cycle (SSC). However, the contributions of ECC and isometric (ISO) strength to the countermovement (CMJ) and depth jump (DJ) remain unclear due to variability in assessment methods (e.g., dynamometry, isometric mid-thigh pull) and the limited range of metrics examined in prior research. The aim of this study was to assess correlations between multi-joint lower extremity MES and MIS, obtained using a seated multi-joint isokinetic dynamometer, and 13 vertical ground reaction force (GRF) measures derived from the performance of three maximal effort DJs and CMJs. Twenty-five healthy young adults participated in this study (age = 21.9 ± 2.9 years). Pearson r correlation coefficients were used to assess the statistical significance (α = 0.05) of the relationships between absolute (N) and body mass normalized (BN) maximal strength measures and vertical jumping metrics. Moderate-to-strong positive correlations were identified between MES and MIS with broad performance metrics in CMJ and DJ, including reactive strength index (r = 0.45–0.53, p < 0.05), modified reactive strength index (r = 0.41–0.62, p < 0.05), and jump height (r = 0.59–0.75, p < 0.05). Moderate-to-strong positive correlations were also observed between MES and MIS with CON work (r = 0.58–0.71, p < 0.05) and CON peak power (r = 0.44–0.71, p < 0.05) for both the CMJ and DJ. In contrast, moderate-to-strong negative correlations were observed between MES and MIS with ECC work (r = 0.42–0.62, p < 0.005) and ECC peak power (r = 0.45–0.60, p < 0.05). These findings suggest that enhanced neuromuscular efficiency and joint stiffness in stronger musculature reduce energy absorption during the eccentric phase, minimizing mechanical deformation and preserving elastic energy for concentric propulsion. Combined, MES and MIS optimize force application, energy utilization, and control, which are crucial for maximizing jump height. These findings underscore the role of MES and MIS in influencing jumping performance across both the ECC and CON phases of the SSC. This insight is valuable for practitioners designing training programs aimed at improving vertical jumping ability. Full article

People affected by mitochondrial myopathies (MITOs) are thought to have impaired skeletal muscle oxygenation. The aims of this study were to measure skeletal muscle mitochondrial capacity in MITO participants and able-bodied (AB) participants and evaluate the influence of muscle-specific endurance training in one MITO participant. Participants (n = 7) with mitochondrial disease and controls (n = 9) were tested (ages 18–54 years). Mitochondrial capacity (mVO₂max) was measured using the rate constant of recovery of oxygen consumption (mVO₂) after exercise in the forearm flexor muscles with near-infrared spectroscopy (NIRS). One MITO participant was tested before and after performing 18 forearm exercise sessions in 30 days. There were no differences between MITO and AB participants in mVO₂max (MITO: 1.4 ± 0.1 min⁻¹; AB: 1.5 ± 0.3 min⁻¹; p = 0.29), resting mVO₂ (MITO: −0.4 ± 0.2%/min; AB: −0.3 ± 0.1%/min; p = 0.23), or initial post exercise oxygen consumption rates (MITO: 4.3 ± 1.2%/min; AB: 4.4 ± 1.4%/min; p = 0.9). Exercise oxygen desaturation was greater in MITO (39.8 ± 9.7% range) than in AB (28 ± 8.8% range) participants, p = 0.02. The MITO participant who trained increased her mitochondrial capacity (58%) and muscle-specific endurance (24%) and had reduced symptoms of muscle fatigue. We found no evidence supporting in vivo impairment of forearm muscle mVO₂max in genetically confirmed MITO participants. This is consistent with studies that report increased mitochondrial content, which offsets the decrease in mitochondrial function. Positive muscle adaptations to endurance training appear to be possible in people with MITOs. Characterization of study populations will be important when interpreting the relationship between in vivo mitochondrial capacity and mitochondrial disease. Full article

Background: The presence of sensorimotor control deficits in adolescent idiopathic scoliosis compared to typically developed adolescents is supported by the literature but lacks reliability studies for assessment in this population. This study aimed to assess the reliability of eight sensorimotor control tests, in terms of static and dynamic balance, joint position sense (JPS) tests of the extremities and the spine, and a functional upper extremity proprioceptive test in adolescent idiopathic scoliosis subjects. Methods: Sixty adolescent idiopathic scoliosis subjects were divided into four groups. Each group underwent two tests by the same examiner, repeated at 15 min intervals. Reliability was measured using the intraclass correlation coefficient (ICC), standard error of measurement (SEM), and smallest detectable difference (SDD). Results: The results showed high reliability for the upper extremity functional proprioception test, for the dynamic and static balance test, and for the spinal lateral flexion joint position sense test in both directions. On the other hand, the shoulder external rotation, knee extension, elbow flexion, and spinal flexion joint position sense tests demonstrated poor reliability in adolescent idiopathic scoliosis subjects. Conclusions: Therapists are recommended to use the functional upper extremity proprioception test, the Fukuda test, the static balance test using a force footplate, and the spinal lateral flexion joint position sense test for assessing treatment progress in this population. Full article