Effects of foam rolling on hamstrings stiffness in damaged and non-damaged muscle states.

Introduction: The aim of this study was to examine the effects of foam rolling (FR) on hamstring muscles stiffness in both non-damaged and exercise-induced muscle damage (EIMD) states, using shear wave ultrasound elastography to measure changes in shear modulus. Methods: Fourteen healthy adults (25.5 ± 4.7 years) participated in a within-participant repeated measures design, with a 2-minute FR intervention applied on one leg and contralateral leg serving as a control. The damaging protocol encompassed maximal eccentric knee extensions performed on an isokinetic dynamometer and the Nordic hamstring exercise, consisting of 3 sets of 10 and 6 repetitions, respectively. Measurement were taken at baseline and then 1 h, 24 h and 48 h after the damaging protocol. Results: The results indicated no significant time × leg interaction for shear modulus in biceps femoris, semimembranosus, and semitendinosus muscles in both non-damaged and damaged states. Notably, there was a significant increase in biceps femoris (p = 0.001; η2 = 0.36) and semitendinosus (p < 0.001; η2 = 0.44) shear modulus after EIMD, but no significant differences were found between the FR and control leg, which was also the case for muscle soreness, range of motion, and passive resistive torque (p = 0.239-0.999 for interactions). Discussion: The absence of significant changes post-FR intervention suggests a limited role of short-duration FR in altering muscle stiffness during recovery from EIMD. These findings contribute to the understanding of FR's role in muscle recovery. Although this was not directly investigated, our results suggest a predominance of central mechanisms rather than direct mechanical modifications in muscle properties. This research highlights the necessity for additional investigations to explore how FR interventions influence muscles in different states and to elucidate the mechanisms underlying these influences.

Is larger eccentric utilization ratio associated with poorer rate of force development in squat jump? An exploratory study.

This exploratory study examines the relationship between the eccentric utilization ratio (EUR) and the rate of force development (RFD) in squat jumps (SJ). EUR, a key metric in sports science, compares performance in countermovement jumps (CMJ) and squat jumps (SJ). The study hypothesizes that a higher EUR is associated with a poorer RFD in SJ. Basketball and soccer players, long-distance runners, alongside physical education students (209 men; age: 23.2 ± 4.95 years and 104 women; age: 22.7 ± 4.42 years) participated. The EUR was calculated from jump height, peak force and peak power. The results indicated a small to moderate but significant negative correlation between EUR based on peak force or peak power and RFD in SJ (r = -.41 and -.27), suggesting that a higher EUR might be linked to a diminished ability to rapidly develop force in SJ. Thus, a higher EUR may not indicate superior athletic performance.

The effects of taping in the management of primary dysmenorrhoea: A systematic review with meta-analysis.

In this systematic review and meta-analysis, we explored the efficacy of taping as a non-pharmacological intervention for pain reduction in primary dysmenorrhoea (PD), a prevalent condition causing significant quality of life impairment. We conducted a comprehensive search across databases including PubMed, PEDro, and Web of Science to identify randomized controlled trials assessing taping's effectiveness in PD for pain relief. Our criteria focused on studies comparing taping to no intervention or alternatives, with pain outcomes primarily measured using the Visual Analogue Scale (VAS). The quality assessment utilized the PEDro scale, with scores ranging from 4 to 8, indicating a spectrum of moderate to high-quality evidence. The results indicate that both kinesiotaping (SMD = -1.22; 95 % CI: -2.15, -0.29; p = 0.01) and other tapes (SMD = -1.61, 95 % CI: -2.15, -0.65; p = 0.001) significantly reduces pain intensity in women with PD. However, the certainty of evidence was very low according to GRADE criteria. This underscores the necessity for further research to understand taping's analgesic mechanisms, its long-term effects, and its influence on related symptoms and overall quality of life. Our findings advocate for the inclusion of taping in PD management, offering a promising direction for enhancing care in affected women.

The Use of Shear-Wave Ultrasound Elastography in the Diagnosis and Monitoring of Musculoskeletal Injuries.

Ultrasound elastography is a valuable method employed to evaluate tissue stiffness, with shear-wave elastography (SWE) recently gaining significance in various settings. This literature review aims to explore the potential of SWE as a diagnostic and monitoring tool for musculoskeletal injuries. In total, 15 studies were found and included in the review. The outcomes of these studies demonstrate the effectiveness of SWE in detecting stiffness changes in individuals diagnosed with Achilles tendinopathy, Achilles tendon rupture, rotator cuff rupture, tendinosis of the long head of the biceps tendon, injury of the supraspinatus muscle, medial tibial stress syndrome, and patellar tendinopathy. Moreover, SWE proves its efficacy in distinguishing variations in tissue stiffness before the commencement and after the completion of rehabilitation in cases of Achilles tendon rupture and patellar tendinopathy. In summary, the findings from this review suggest that SWE holds promise as a viable tool for diagnosing and monitoring specific musculoskeletal injuries. However, while the field of ultrasound elastography for assessing musculoskeletal injuries has made considerable progress, further research is imperative to corroborate these findings in the future.

Sensorimotor and proprioceptive exercise programs to improve balance in older adults: a systematic review with meta-analysis.

The primary aim of this study was to systematically review and meta-analyze the impact of sensorimotor and proprioceptive exercises on balance in older adults. We also sought to define how researchers describe proprioceptive and sensory-motor training and their respective protocols. The review was conducted following the PRISMA guidelines, with searches performed in March 2023. Both authors carried out independent searches using the PubMed and PEDro databases. From a total of 320 identified records, 12 studies were deemed eligible for meta-analysis after screening and removal of duplicates. The average PEDro score was 5.11 ± 1.11 indicating overall fair quality of studies.  Common outcome measures included the Berg balance scale, Timed up and go test, Tinetti balance scale, Functional reach test and various single-leg stance tests. All outcomes were significantly improved by the interventions (standard mean difference = 0.65 - 1.29), with little difference between proprioceptive and sensorimotor training. However, the quality of evidence ranged from "very low" to "low" based on GRADE guidelines, suggesting further high-quality studies are needed. This review underscores the potential benefits of sensorimotor and proprioceptive exercises for enhancing balance in older adults, while also highlighting the ambiguity and inconsistency regarding the usage of the terms proprioceptive and sensorimotor training.

Differential Effects of Classical vs. Sports Massage on Erector Spinae and Upper Trapezius Muscle Stiffness: A Shear-Wave Elastography Study in Young Women.

Classical and sports massages are commonly used interventions, but their comparative effects on muscle stiffness remain unclear. Classical massage is more general and uses light to moderate pressure, and its main purpose is relaxation. Sports massage, on the other hand, is more specialized and targets the unique needs of massaged individuals using moderate to firm pressure. This study aimed to evaluate the impacts of classical and sports massages on the stiffness of the erector spinae (ES) and upper trapezius (UT) muscles. Fifteen recreationally active young women, aged 22.9 ± 1.2 years, underwent a randomized cross-over study (with three conditions). Participants received either a five-minute classical or sports massage or a passive rest as a control on distinct days. Muscle stiffness was assessed using shear-wave elastography. The ES shear modulus displayed a significant time effect (p < 0.001; η2 = 0.515) without noticeable differences between the conditions, and the time × massage-type interactions approached statistical significance (F = 2.014; p = 0.073). There was also a large and statistically significant effect of the time on the UT (F = 11.127; p < 0.001; η2 = 0.443). We could not prove that classical and sports massages reduced muscle stiffness. The absence of significant differences might be attributed to the specific intervention parameters (massage duration of 5 min) and the small, only young women sample size. Given some tendencies towards significant effects, larger sample sizes are needed to further investigate this research question.

Acute effects of static and proprioceptive neuromuscular facilitation stretching on hamstrings muscle stiffness and range of motion: a randomized cross-over study.

This study aimed to compare the acute effects of static stretching (SS) and proprioceptive neuromuscular facilitation (PNF) stretching on hamstrings flexibility and shear modulus. Sixteen recreationally active young volunteers participated in a randomized cross-over study. Participants underwent an aerobic warm-up (WU), followed by either SS or PNF stretching. Range of motion (RoM) during passive straight leg raise and active knee extension, as well as shear modulus of the biceps femoris (BF) and semitendinosus (ST) muscles, were measured at baseline, post-WU, and post-stretching. Both stretching techniques significantly increased RoM, with no differences observed between SS and PNF (p < 0.001; η2 = 0.59-0.68). However, only PNF stretching resulted in a significant decrease in BF shear modulus (time×stretching type interaction: p = 0.045; η2 = 0.19), indicating reduced muscle stiffness. No changes in ST shear modulus were observed after either stretching technique. There was no significant correlation between changes in RoM and shear modulus, suggesting that the increase in RoM was predominantly due to changes in stretch tolerance rather than mechanical properties of the muscles. These findings suggest that both SS and PNF stretching can effectively improve hamstring flexibility, but PNF stretching may additionally reduce BF muscle stiffness. The study highlights the importance of considering individual muscle-specific responses to stretching techniques and provides insights into the mechanisms underpinning acute increases in RoM.

The Prevalence of Impostor Phenomenon in Medical Students in Slovenia: Effects of Gender, Year of Study, and Clinical Work Experience.

Phenomenon: Impostor syndrome (IS) is manifested in the fear of failing and being exposed as incompetent, despite exceptional professional performance. IS has been recognized in many professions, including medicine. Understanding IS prevalence and risk factors is critical to ensure the well-being of medical students and, by extension, future physicians. Approach: It was expected that IS is highly prevalent in medical students, higher in women and associated with year of study and prior clinical experience. The Clance Impostors Phenomenon Scale (CIPS) was used to collect the responses from of medical students in May 2023. Questionnaires were distributed online to both public medical faculties in Slovenia. Findings: 207 medical students (157 women, 50 men; mean age: 23.2 ± 2.6 years) completed the questionnaire (response rate = 13.1%). Women exhibited higher CIPS scores (66.0 ± 13.9) compared to men (58.8 ± 15.1) (p = 0.005). Neither age (r = 0.05; p = 0.464) nor year of study (r = 0.03; p = 0.653) was correlated with CIPS score. There were also no differences in CIPS score between students with (63.4 ± 15.2) and without (64.7 ± 13.9) prior clinical work experience (p = 0.531). Insights: The results of the present study suggest that IS can occur at any stage of medical education, with a slightly higher prevalence in women. This study contributes to the understanding of IS among medical students and calls for addressing environmental factors and taking supportive measures to mitigate the impact of IS and promote medical students' well-being and success.

Potential of molecular biophysical stimulation therapy in chronic musculoskeletal disorders: a narrative review.

Current treatment of chronic musculoskeletal diseases does not give sufficient results despite the implementation of novel drugs and techniques in orthopaedics and physical therapy. For instance, osteoporosis treatment is currently mainly limited to drug application, while the goal of osteoarthritis treatment is to mitigate pain symptoms through physical therapy. The main therapeutic principle in the management of osteoporosis is not only to increase bone mass, but also to improve bone and the cartilage quality, which depends on the biomechanical balance. Therefore, there is a strong demand for advanced technologies that would safely and non-invasively accelerate cartilage regeneration and improve bone density. Ten years ago, a new state-of-the-art technology - "Molecular biophysical stimulation therapy (MBST)", specifically nuclear magnetic resonance therapy, emerged on the medical technology market and until now, it has shown successful results in the conservative treatment of musculoskeletal disorders, including back pain. The aim of this review is to provide an integrated, synthesized overview of the current evidence of efficacy of MBST for managing chronic musculoskeletal disorders.

Which muscles exhibit increased stiffness in people with chronic neck pain? A systematic review with meta-analysis.

Introduction: Chronic neck pain (CNP) substantially impacts quality of life, posing both personal challenges and economic strains. This systematic review sought to discern muscle-specific stiffness differences between CNP patients and individuals without CNP. Methods: We searched the PubMed, Scopus, and PEDro databases for studies using ultrasound elastography or myotonometry to compare muscle stiffness between CNP patients and asymptomatic controls. Using a meta-analysis with a random-effects model, we derived the pooled effect as standardized mean difference (SMD). Results: Out of the six studies selected, the adjusted Newcastle-Ottawa rating scale for cross-sectional studies denoted three as moderate-quality and three as high-quality. Our findings indicate that the upper trapezius (UT) stiffness was elevated in CNP patients compared to their counterparts without CNP (SMD = 0.39, 95% CI = 0.05 to 0.74; p = 0.03; small effect size). The data for other muscles remained inconclusive. Discussion: Given the case-control design of all reviewed studies, a direct causative link between UT stiffness and CNP is yet to be confirmed. As such, recommending a reduction in trapezius muscle stiffness as a primary rehabilitation strategy for CNP patients is still inconclusive and further research is needed.

Influence of unilateral and bilateral knee extension fatigue protocols on inter-limb asymmetries assessed through countermovement jumps.

This study explores the sensitivity of jump type (unilateral and bilateral) and output variable (mean force, propulsive impulse, and jump height) to detect the changes in inter-limb asymmetries induced by unilateral and bilateral fatigue protocols. Thirty-eight individuals performed two testing sessions that consisted of (I) nine "pre-fatigued" countermovement jumps (CMJs; three bilateral and six unilateral [three with each leg]), (II) fatigue protocol and (III) nine "post-fatigued" CMJs. The testing sessions only differed in the fatigue protocol (five sets to failure against the 15-repetition maximum load using either the unilateral or bilateral knee extension exercise). The magnitude of all CMJ-derived variables (mean force, impulse, and jump height) decreased following both unilateral (p ≤ 0.002) and bilateral fatigue protocols (p ≤ 0.018). However, only unilateral protocol accentuated inter-limb asymmetries, which was detected for all variables during the unilateral CMJ (from -4.33% to -2.04%; all p < 0.05) but not during the bilateral CMJ (from -0.64% to 0.54%; all p > 0.05). The changes in inter-limb asymmetries following the unilateral and bilateral fatigue protocols were not significantly correlated between the unilateral and bilateral CMJs (rs ≤ 0.172). The unilateral CMJ should be recommended for the testing purposes over the bilateral CMJ due to its greater sensitivity to detect the selective effects of fatigue.

Stretching and Releasing of Iliotibial Band Complex in Patients with Iliotibial Band Syndrome: A Narrative Review.

Iliotibial band syndrome (ITBS) is one of the most common overuse syndromes causing knee pain; it is especially prevalent in runners and also common in cyclists, rowers, and field athletes, with occasional cases occurring in non-athletes too. ITBS symptoms can negatively affect not only knee function, but also mental and physical aspects of health-related quality of life. Although various conservative treatment options have been investigated and discussed, there is still no consensus on a standard of care for ITBS. Moreover, the literature on the etiology and risk factors of ITBS, which could help in selecting appropriate treatment methods, is conflicting and inconclusive. The role of individual treatment modalities such as stretching and releasing techniques has not been extensively studied and remains unclear. In this article, we will critically review the available evidence for the benefits of ITB stretching and "release" methods in the treatment of ITBS. In addition to the direct evidence (clinical studies examining the effects of ITB stretching and other methods that purportedly stretch or "release" the ITB), we present several additional lines of reasoning that discuss the rationale for ITB stretching/releasing in terms of the etiology of ITBS, the mechanical properties and behavior of the ITB, and the risk factors for ITBS development. We conclude that the current literature provides some evidence for the inclusion of stretching or other "release" methods in the early rehabilitation of ITBS. Long-term interventions typically include ITB stretching; however, it remains unclear to what extent stretching within a multimodal treatment actually contributes to resolving the symptoms. At the same time, there is no direct evidence to suggest that stretching and "release" methods have any negative effects.

The relationship between elastography-based muscle properties and vertical jump performance, countermovement utilization ratio, and rate of force development.

This study explored the relationships between passive muscle stiffness (shear modulus) and vertical jumping performance, countermovement utilization ratio (CUR) and rate of force development (RFD) in an attempt to unravel the mechanism that may explain the association between shear modulus and performance. 32 recreationally active participants (16 males, 16 females; age: 22.4 ± 5.1 years) participated. Shear modulus was assessed for the lateral and medial gastrocnemius (GL and GM), and vastus medialis (VM) and lateralis (VL) muscles using shear wave elastography. Squat jump (SJ) and countermovement (CMJ) jump were determined, with CUR being expressed as the ratio between the two. RFD in ankle and knee extension tasks was measured using isometric dynamometers. Our results suggest that within a heterogeneous group of recreational athletes, passive muscle stiffness is not related to RFD and jump performance, but positively related to CUR. In males, shear modulus of the GL was positively related to SJ height (r = 0.55). We also found inverse moderate correlations between VL and VM shear modulus and RFD in females only (r = -0.50 to -0.51), but this relationship was possibly affected by age and body fat content. Different mechanisms may underpin the association between shear modulus and performance depending on the muscle, task and population investigated.

Incidence and Duration of Sick Leave Due to Work-Related Musculoskeletal Disorders in the Accommodation and Food Services Activities Sector in Slovenia: A Nationwide 5-Year Observational Study.

OBJECTIVES: The aim of this study was to analyze Slovenian data on sick leave (SL) due to the most common work-related musculoskeletal disorders (MSDs) among workers in sector I "accommodation and food services activities" from the NACE Rev2 classification. METHODS: We investigated both SL incidence (i.e., number of cases) and disease severity (i.e., average SL duration) by body site, gender, age and divisions within the sector. In addition, trends in SL data (difference between 2015 and 2019) were analyzed. The effect of age group, gender and division was also assessed with relative risk (RR). RESULTS: Female gender was associated with higher risk of MSDs in young (RR = 1.91 (1.53-2.43)) and older (RR = 2.24 (1.90-2.65)) subgroups. Older age was associated with greater SL incidence and longer SL duration, regardless of gender and division within sector I. This was also reflected in relative risk calculations between older and younger groups (females: RR = 4.43; CI = 3.75-5.01; p < 0.001; males: RR = 3.71; CI = 2.89-4.77; p < 0.001). Low back disorders were the most frequent cause for SL, while lower limb disorders tended to cause the longest average SL. The SL durations were similar across divisions within the sector, while the incidence rate tended to be higher in the "accommodation" than the "food and beverage services" division. CONCLUSIONS: Special attention needs to be paid to reducing the risk of low back disorders, which are by far the most common cause of SL, and lower limb disorders, which cause the longest SL. We recommend the implementation of countermeasures that focus on early detection and rapid treatment/recovery of MSDs in older workers.

The prevalence and severity of sick-leaves due to musculoskeletal disorders among workers in water supply; sewerage, waste management and remediation activities.

The aim of this study was to analyse the nationwide data on sick leaves (SL) due to work-related musculoskeletal disorders among Slovenian workers in section E "water supply; sewerage, waste management and remediation activities" from NACE Rev2 classification. We report both, SL frequency (ie, number of cases) and SL severity (ie, average SL duration), stratified by body region, gender, age and divisions within the section. In addition, trends in SL data (year 2015-2019 difference) were analyzed. Throughout the analysed years, ∼9,000 workers were employed in the section, with male to female ratio at ∼ 4:1. The major findings are as follows: (i) low back disorders were by far the most prevalent, however, the mean SL duration was the highest for lower limb disorders; (ii) older age was associated with increased SL frequency and duration, irrespective of gender; (iii) male gender was consistently associated with larger SL duration, while the data on SL frequency is inconclusive, as older females had more frequent SL than older males; (iv) the effect of division was relatively minor and the comparisons are limited due to large discrepancies regarding the number of workers across divisions; (v) a slight increasing trend for both SL frequency and duration was observed from 2015 to 2019. In conclusion, particular attention in terms of early diagnosis and treatment of musculoskeletal disorders should be given to male workers and older workers in general in section E.

Effects of 12-week full body resistance exercise on vertical jumping with and without military equipment in Slovenian Armed Forces.

INTRODUCTION: Jumping ability is one of the most important physical qualities in military personnel. Previous training intervention studies have shown equivocal effects on jumping ability. In this study, we assessed the effect of a 12-week resistance exercise programme on countermovement jump (CMJ) performance with and without military equipment. METHODS: Ninety-six members of the Slovenian Armed Forces (age range 20-47 years) were allocated to the intervention (n=65) and the control (n=32) group. The intervention group performed 2 sessions of full body resistance exercise per week for 12 weeks, while the control group continued with their regular training routine. Before and after the intervention, CMJ assessment using force plates was conducted with and without military equipment. RESULTS: CMJ testing with and without equipment both exhibited high to excellent relative and absolute reliability. The intervention elicited statistically significant (p=0.011-0.026; η2=0.05-0.06), but small improvements in CMJ height when performed without equipment (from 28.2±3.8 cm to 29.5±3.3 cm) and with equipment (from 25.3±3.7 cm to 27.1±6.1). Other variables showed even smaller or trivial changes. CONCLUSIONS: This study suggests that CMJ with equipment could be a reliable tool to assess jumping performance specific to requirements of military work, which would increase the ecological validity of the testing. The present structured full-body training intervention showed modest improvements in jumping ability in both testing conditions. TRIAL REGISTRATION NUMBER: NCT0341546.

The Effects of Conservative Interventions for treating Diastasis Recti Abdominis in Postpartum Women: a Review with Meta-analysis.

Diastasis recti abdominis (DRA) is a common occurrence in postpartum women, and it is unclear what types of nonsurgical interventions are most effective in preventing and/or reducing it. The aim of this review with meta-analysis was to investigate which conservative treatment approaches are the most effective for the management of postpartum DRA. After a thorough search of the PubMed and Scopus databases, we reviewed 14 articles. The literature suggests that abdominal exercise programs are generally effective in treating DRA at various postpartum periods. There is preliminary but promising evidence of the efficacy of electrical stimulation in combination with exercise. In addition, abdominal kinesiotaping can be used in conjunction with other interventions. Limitations of previous research include (a) the use of different measurement methods (palpation, calipers, ultrasound) and sites, (b) the evaluation of treatment effects in different time periods, and (c) the use of a wider range of exercise combinations. Although abdominal exercise is a cornerstone of DRA treatment, the optimal exercise combination is currently unknown due to these limitations.

Comparison of Vertical and Horizontal Reactive Strength Index Variants and Association With Change of Direction Performance.

ABSTRACT: Sarabon, N, Kozinc, Z, and Bishop, C. A comparison of vertical and horizontal reactive strength index variants and association with change of direction performance. J Strength Cond Res 37(1): 84-90, 2023-This study sought to investigate the interrelationship between different vertical and horizontal variants of reactive strength index (RSI) and change of direction (CoD) performance. Thirty-one male volleyball players (age: 22.4 ± 3.9 years) performed bilateral drop jumps (DJs), bilateral and unilateral countermovement jumps (CMJs), and triple hops for distance. The RSI was calculated as the ratio of jump height and contact time (DJ), jump height and time to takeoff (CMJ), flight time or hop distance and contact time (triple hop), and 505 CoD test. Reactive strength index obtained from DJ and CMJ tasks exhibited excellent trial-to-trial reliability (intraclass correlation coefficient [ICC] = 0.91-0.94), whereas triple hop-based RSI had only moderate reliability (ICC = 0.67-0.74). The relationships among different RSI variants were moderate to high (i.e., DJ to CMJ: r = 0.57-0.69, p ≤ 0.004; DJ to triple hop: r = 0.54-0.66, p ≤ 0.021; and CMJ to triple hop: r = 0.42-0.63, p ≤ 0.037). For the triple hop, the associations between RSI based on hop flight time and RSI based on hop distance were high for hop 1-2 (r = 0.77-0.83; p < 0.001) and very high for hop 2-3 (r = 0.91-0.92; p < 0.001). All RSI variants were in small to moderate negative correlation with 505 test performance (r = -0.38 to -0.45; p ≤ 0.042). The agreement in interlimb asymmetry direction between RSI from unilateral CMJ and triple hop RSI variables was slight to moderate (kappa coefficient = 0.06-0.36). In conclusion, although interrelationships between RSI variants were moderate to high, the direction of interlimb asymmetry was inconsistent, highlighting the notion of movement variability in limb dominance.

The Effects of Isometric Fatigue on Trunk Muscle Stiffness: Implications for Shear-Wave Elastography Measurements.

Muscle stiffness has been implicated as a possible factor in low back pain risk. There are few studies on the effects of isometric fatigue on the shear modulus of trunk muscles. This study aimed to investigate the effects of trunk isometric fatigue on the passive and active (during low and high-level contractions) shear moduli of the erector spinae (ES) and superficial and deep multifidus (MF) muscles. We assessed passive and active shear modulus using shear-wave elastography in healthy young participants (n = 22; 11 males, 11 females), before and after an isometric trunk extension fatigue protocol. Maximal voluntary force decreased from 771.2 ± 249.8 N before fatigue to 707.3 ± 204.1 N after fatigue (-8.64%; p = 0.003). Passive shear modulus was significantly decreased after fatigue in the MF muscle (p = 0.006-0.022; Cohen's d = 0.40-46), but not the ES muscle (p = 0.867). Active shear modulus during low-level contraction was not affected by fatigue (p = 0.697-0.701), while it was decreased during high-level contraction for both muscles (p = 0.011; d = 0.29-0.34). Sex-specific analysis indicated the decrease in ES shear modulus was significant in males (p = 0.015; d = 0.31), but not in females (p = 0.140). Conversely, the shear modulus in superficial MF had a statistically significant decrease in females (p = 0.002; d = 0.74) but not in males (p = 0.368). These results have important implications for further investigations of the mechanistic interaction between physical workloads, sex, muscle stiffness (and other variables affecting trunk stability and neuromuscular control), and the development/persistence of low back pain.

Acute Effects of Beetroot Juice Supplementation on Isometric Muscle Strength, Rate of Torque Development and Isometric Endurance in Young Adult Men and Women: A Randomized, Double-Blind, Controlled Cross-Over Pilot Study.

This study was conducted to investigate the effect of concentrated beetroot juice on isometric strength and knee extensor muscle endurance in healthy adults. We conducted a randomized cross-over, double-blind experiment in which participants (18 healthy, physically active adults, 9 men, 9 women) consumed either concentrated beetroot juice (140 mL) or low-nitrate control supplement 2.5 h before the measurement. Isometric maximum strength (peak torque), explosive strength (isometric rate of torque development), and strength endurance at 50% of peak torque were measured on an isometric dynamometer. The results showed that concentrated beetroot juice had no effect on the maximum voluntary isometric strength and rate of torque development of the knee extensors. The only exception was the maximum rate of torque development, for which a positive influence was demonstrated only in men. As for the endurance of the knee extensors, the supplement had a positive effect in men (endurance time increased from 86.4 ± 46.1 s to 103.4 ± 53.7 s; p = 0.022), but not in women. The absence of effect on maximal voluntary strength is consistent with previous research. One the other hand, improvements in endurance and rate of torque development in men only point to an important aspect of a previously under-researched area of sex-specific responses to nitrate supplementation.