Biomedical Beliefs Explain the Clinical Decisions Made by Exercise-Based Practitioners for People With Chronic Low Back Pain.

STUDY DESIGN: Cross-sectional survey. OBJECTIVE: This study surveyed the attitudes and beliefs of physiotherapists and accredited exercise physiologists (AEP) toward chronic low back pain (CLBP), in Australia. The objective of this study was to investigate the effect of biomedical and biopsychosocial attitudes and beliefs toward CLBP on clinical decision making in exercise-based practitioners. SUMMARY OF BACKGROUND DATA: The attitudes and beliefs of AEPs toward CLBP have not been studied. Literature regarding physiotherapists suggests a biomedical approach leading to more conservative treatment and on occasion, treatment going against practice guidelines. METHODS: Seventy five AEPs and 75 physiotherapists were surveyed using the pain attitudes and beliefs scale for physiotherapists, which consists of both a biomedical and biopsychosocial subscale. Clinical decision making was assessed using two patient vignettes. RESULTS: AEPs held higher biomedical beliefs compared with physiotherapists. No between-group differences were observed on the biopsychosocial subscale. Indeed, biomedical attitudes and beliefs did explain clinical decision making with higher scores reflecting a more conservative approach. However, biomedical beliefs influenced decision making regardless of profession. CONCLUSION: Biomedical attitudes and beliefs regarding CLBP influence clinical decision making in exercise-based practitioners, regardless of profession. AEPs reported higher biomedical scores, suggesting more frequent choice of conservative care. Thus, patients may receive inconsistent care and advice from practitioners within the same field. Based on clinical practice guidelines and the positive associations on clinical decision making of the biopsychosocial model, it is necessary to understand how best to provide exercise-based practitioners with education on how to apply a biopsychosocial approach to CLBP.Level of Evidence: 3.

Changes in Unilateral Upper Limb Muscular Strength and Electromyographic Activity After a 16-Week Strength Training Intervention in Survivors of Breast Cancer.

Hagstrom, AD, Shorter, KA, and Marshall, PWM. Changes in unilateral upper limb muscular strength and Electroymographic activity after a 16-week strength training intervention in survivors of breast cancer. J Strength Cond Res 33(1): 225-233, 2019-Upper limb strength deficits are frequently observed following breast cancer (BC) and its treatments. It is currently unknown whether these unilateral deficits can be corrected by a standard bilateral strength training intervention. Twenty-three survivors of BC were included in this analysis. Fourteen performed a 16-week resistance training (RT) intervention, 9 were assigned to a usual care waitlist control group. Electromyographic analysis of the pectoralis major and triceps brachii were monitored during 3 maximal isometric contractions and a fatiguing endurance task. Muscular strength was significantly different between limbs at the start of the intervention (p = 0.02). Electromyographic amplitude and median frequency did not differ between limbs at the start of the intervention. Muscular strength was significantly different between limbs in the RT group at the end of the intervention (p = 0.01). Electromyographic amplitude did not differ between limbs or groups at the end of the intervention. Bilateral strength training did not correct the unilateral strength deficit observed in this group of survivors of breast cancer. Periods of unilateral strength training should be implemented into periodized RT programs in this cohort.

Anticipatory and compensatory postural adjustments in people with low back pain: a systematic review and meta-analysis.

BACKGROUND CONTEXT: Despite altered anticipatory (APAs) and compensatory postural adjustments (CPAs) being hypothesized to contribute to the onset and persistence of low back pain (LBP), results from studies comparing people with and without LBP are conflicting. PURPOSE: This systematic review aimed to determine whether APAs or CPAs are altered in the presence of acute and chronic LBP. STUDY DESIGN: A systematic review of studies was carried out. PATIENT SAMPLE: No patient sample was required. OUTCOME MEASURES: Between group standardized mean differences and 95% confidence intervals for APAs ad CPAs METHODS: A comprehensive search was conducted for articles comparing people with LBP (acute or chronic) to healthy controls for the onset or amplitude of muscle activity, center of pressure (COP), or kinematic responses to expected or unexpected perturbations. Two independent reviewers extracted data and assessed the methodological quality of relevant studies. Differences between people with and without LBP were calculated as standardized mean differences, and included in a meta-analysis if outcomes were homogeneous. Otherwise, a narrative synthesis was conducted. RESULTS: Twenty-seven studies were included, of which the majority examined muscle onsets in response to expected and unexpected perturbations. Only two studies compared people with and without acute LBP, and results for these studies were conflicting. The results show delayed muscle onsets in response to expected and unexpected perturbations for people with chronic LBP when compared with healthy controls. No conclusive evidence for differences between people with and without chronic LBP for COP or kinematic responses. CONCLUSIONS: There is currently no convincing evidence of differences between people with and without acute LBP for APAs or CPAs. Conversely, delayed muscle onsets in people with chronic LBP suggest APAs and CPAs are altered in this population. However, the functional relevance of these delayed muscle onsets (eg, COP and kinematics) is unknown.

Acute attenuation of fatigue after sodium bicarbonate supplementation does not manifest into greater training adaptations after 10-weeks of resistance training exercise.

PURPOSE: In two concurrent studies, we aimed to a) confirm the acute effect of 0.3 g·kg-1 body weight (BW) sodium bicarbonate (NaHCO3) supplementation on central and peripheral mechanisms associated with explosive power (Study 1) and b) determine whether chronic NaHCO3 supplementation would improve the adaptive response of the neuromuscular system during a 10-week resistance training program (Study 2). METHODS: Eight resistance trained participants volunteered after providing written consent. The experimental design consisted of a week of baseline testing, followed by ten weeks of training with progress measures performed in Week 5. Study 1 involved neuromuscular measurements before and after the leg extension portion of a power based training session performed in Week 1. Changes in maximal torque (MVT) and rates of torque development (RTD), along with other variables derived from femoral nerve stimulation (e.g. voluntary activation, neural recruitment) were analysed to determine the extent of fatigue under NaHCO3 or placebo conditions. Changes in these same variables, coupled with functional 1-repetition maximum leg extension strength, were measured in Study 2 from baseline (Week 0) to Week 5, and again at Week 10. RESULTS AND CONCLUSION: In Study 1, we observed a decline after the leg extension task in both MVT (~ 30%) and rates of torque production (RTD) irrespective of acid-base status, however the decline in maximal RTD (RTDMAX) was nearly 20% less in the NaHCO3 condition when compared to placebo (mean difference of 294.8 ± 133.4 Nm·s-1 (95% CI -583.1 to -6.5 Nm, p < 0.05)). The primary finding in Study 2, however, suggests that introducing NaHCO3 repeatedly during a 10-week RT program does not confer any additional benefit to the mechanisms (and subsequent adaptive processes) related to explosive power production.

The fatigue of a full body resistance exercise session in trained men.

OBJECTIVES: We examined the fatigue and recovery for 48h following a full-body resistance exercise session in trained men. DESIGN: Experimental cross-sectional study. METHODS: Eight resistance trained men volunteered to participate (mean±SD; age 27.0±6.0 years, height 1.79±0.05m, weight 81.8±6.8kg, training experience 7.8±5.0 years). Fatigue and pain was measured before, after, 1h post, 24h and 48h post the full-body resistance exercise session, which was based on in-season models used in contact team sports (e.g. AFL, NRL). Other measures included maximal torque and rate of torque development, central motor output (quadriceps muscle activation, voluntary activation, H-reflexes), and muscle contractility (evoked twitch responses). Linear mixed-model ANOVA procedures were used for data analysis. RESULTS: Fatigue, soreness, and muscle pain did not return to pre-exercise levels until after 48h rest. Quadriceps maximal torque and muscle contractility were reduced from pre-exercise (p<0.01), and did not return to pre-exercise levels until 24h. Early rates of torque development and muscle activation were unchanged. The amplitude and slope of the normalized quadriceps H-reflex was higher immediately after exercise (p<0.05). CONCLUSIONS: Full-body resistance exercise including multiple lower limb movements immediately reduced maximal torque, muscle contractility, and increased pain. While recovery of voluntary and evoked torque was complete within a day, 48h rest was required for fatigue and pain to return to baseline. Maximal voluntary effort may be compromised for lower-limb training (i.e. sprinting, jumping) prescribed in the 48h after the session.

Improved compensatory postural adjustments of the deep abdominals following exercise in people with chronic low back pain.

The purpose of this study was to determine if 8 weeks of exercise affects motor control in people with chronic low back pain (CLBP), measured by anticipatory (APAs) and compensatory postural adjustments (CPAs). APAs and CPAs were measured prior to and following 8 weeks in two groups of people with CLBP: an exercise group (n=12) who attended three exercise sessions per week for 8 weeks; and a non-exercise control group (n=12) who were advised to continue their usual activities for the duration of the study. APAs and CPAs were recorded during unilateral arm flexion, bilaterally from rectus abdominis (RA), transverse abdominis/internal oblique (TA/IO), and erector spinae (ES) via surface electromyography. Analysis of muscle onsets and APA amplitudes suggests APAs did not change for either group. Ipsi-lateral TA/IO CPAs increased for the exercise group and ipsi-lateral TA/IO CPAs decreased for the control group. Only exercise promoted a pattern of TA/IO activity during CPAs similar to healthy individuals, suggesting improved control of rotational torques. These results show motor control improvement following exercise in people with CLBP, highlighted by improved side specific control of TA/IO.

The effects of d-aspartic acid supplementation in resistance-trained men over a three month training period: A randomised controlled trial.

CONTEXT: Research on d-aspartic acid (DAA) has demonstrated increases in total testosterone levels in untrained men, however research in resistance-trained men demonstrated no changes, and reductions in testosterone levels. The long-term consequences of DAA in a resistance trained population are currently unknown. OBJECTIVE: To evaluate the effectiveness of DAA to alter basal testosterone levels over 3 months of resistance training in resistance-trained men. DESIGN: Randomised, double-blind, placebo controlled trial in healthy resistance-trained men, aged 18-36, had been performing regular resistance training exercise for at least 3 d.w-1 for the previous 2 years. Randomised participants were 22 men (d-aspartic acid n = 11; placebo n = 11) (age, 23.8±4.9 y, training age, 3.2±1.5 y). INTERVENTION: D-aspartic acid (6 g.d-1, DAA) versus equal-weight, visually-matched placebo (PLA). All participants performed 12 weeks of supervised, periodised resistance training (4 d.w-1), with a program focusing on all muscle groups. MEASURES: Basal hormones, total testosterone (TT), free testosterone (FT), estradiol (E2), sex-hormone-binding globulin (SHBG) and albumin (ALB); isometric strength; calf muscle cross-sectional area (CSA); calf muscle thickness; quadriceps muscle CSA; quadriceps muscle thickness; evoked V-wave and H-reflexes, were assessed at weeks zero (T1), after six weeks (T2) and after 12 weeks (T3). RESULTS: No change in basal TT or FT were observed after the intervention. DAA supplementation (n = 10) led to a 16%, 95% CI [-27%, -5%] reduction in E2 from T1-T3 (p<0.01). The placebo group (n = 9) demonstrated improvements in spinal responsiveness (gastrocnemius) at the level of the alpha motoneuron. Both groups exhibited increases in isometric strength of the plantar flexors by 17%, 95% CI [7%, 28%] (p<0.05) as well as similar increases in hypertrophy in the quadriceps and calf muscles. CONCLUSIONS: The results of this paper indicate that DAA supplementation is ineffective at changing testosterone levels, or positively affecting training outcomes. Reductions in estradiol and the blunting of peripheral excitability appear unrelated to improvements from resistance training. TRIAL REGISTRATION: Australian New Zealand Clinical Trials Registry ACTRN12617000041358.

Physical activity and the mediating effect of fear, depression, anxiety, and catastrophizing on pain related disability in people with chronic low back pain.

BACKGROUND: Chronic low back pain is a worldwide burden that is not being abated with our current knowledge and treatment of the condition. The fear-avoidance model is used to explain the relationship between pain and disability in patients with chronic low back pain. However there are gaps in empirical support for pathways proposed within this model, and no evidence exists as to whether physical activity moderates these pathways. METHODS: This was a cross-sectional study of 218 people with chronic low back pain. Multiple mediation analyses were conducted to determine the role of fear, catastrophizing, depression, and anxiety in the relationship between pain and disability. Separate analyses were performed with physical activity as the moderator. Individuals were classified as performing regular structured physical activity if they described on average once per week for > 30-minutes an activity classified at least moderate intensity (≥ 4-6 METs), activity prescribed by an allied health professional for their back pain, leisure time sport or recreation, or self-directed physical activity such as resistance exercise. RESULTS: Fear, catastrophizing, and depression significantly mediated the relationship between pain and disability (p<0.001). However the mediating effect of catastrophizing was conditional upon weekly physical activity. That is, the indirect effect for catastrophizing mediating the relationship between pain and disability was only significant for individuals reporting weekly physical activity (B = 1.31, 95% CI 0.44 to 2.23), compared to individuals reporting no weekly physical activity (B = 0.21, 95% CI -0.50 to 0.97). Catastrophizing also mediated the relationship between pain and fear (B = 0.37, 95% CI 0.15 to 0.62), with higher scores explaining 53% of the total effect of pain on fear. CONCLUSIONS: These results support previous findings about the importance of fear and depression as factors that should be targeted in low back pain patients to reduce back pain related disability. We have also extended understanding for the mediating effect of catastrophizing on back pain related disability. Back pain patients engaged with regular physical activity may require counselling with regards to negative pain perceptions.

Mechanistic Insights into the Efficacy of Sodium Bicarbonate Supplementation to Improve Athletic Performance.

A large proportion of empirical research and reviews investigating the ergogenic potential of sodium bicarbonate (NaHCO3) supplementation have focused predominately on performance outcomes and only speculate about underlying mechanisms responsible for any benefit. The aim of this review was to critically evaluate the influence of NaHCO3 supplementation on mechanisms associated with skeletal muscle fatigue as it translates directly to exercise performance. Mechanistic links between skeletal muscle fatigue, proton accumulation (or metabolic acidosis) and NaHCO3 supplementation have been identified to provide a more targeted, evidence-based approach to direct future research, as well as provide practitioners with a contemporary perspective on the potential applications and limitations of this supplement. The mechanisms identified have been broadly categorised under the sections 'Whole-body Metabolism', 'Muscle Physiology' and 'Motor Pathways', and when possible, the performance outcomes of these studies contextualized within an integrative framework of whole-body exercise where other factors such as task demand (e.g. large vs. small muscle groups), cardio-pulmonary and neural control mechanisms may outweigh any localised influence of NaHCO3. Finally, the 'Performance Applications' section provides further interpretation for the practitioner founded on the mechanistic evidence provided in this review and other relevant, applied NaHCO3 performance-related studies.

Relative abdominal adiposity is associated with chronic low back pain: a preliminary explorative study.

BACKGROUND: Although previous research suggests a relationship between chronic low back pain (cLBP) and adiposity, this relationship is poorly understood. No research has explored the relationship between abdominal-specific subcutaneous and visceral adiposity with pain and disability in cLBP individuals. The aim of this study therefore was to examine the relationship of regional and total body adiposity to pain and disability in cLBP individuals. METHODS: A preliminary explorative study design of seventy (n = 70) adult men and women with cLBP was employed. Anthropometric and adiposity measures were collected, including body mass index, waist-to-hip ratio, total body adiposity and specific ultrasound-based abdominal adiposity measurements. Self-reported pain and disability were measured using a Visual Analogue Scale (VAS) and the Oswestry Disability Index (ODI) questionnaires respectively. Relationships between anthropometric and adiposity measures with pain and disability were assessed using correlation and regression analyses. RESULTS: Significant correlations between abdominal to lumbar adiposity ratio (A-L) variables and the waist-to-hip ratio with self-reported pain were observed. A-L variables were found to predict pain, with 9.1-30.5 % of the variance in pain across the three analysis models explained by these variables. No relationships between anthropometric or adiposity variables to self-reported disability were identified. CONCLUSIONS: The findings of this study indicated that regional distribution of adiposity via the A-L is associated with cLBP, providing a rationale for future research on adiposity and cLBP.

Acute neuromuscular and performance responses to Nordic hamstring exercises completed before or after football training.

The optimal scheduling of Nordic Hamstring exercises (NHEs) relative to football training sessions is unknown. We examined the acute neuromuscular and performance responses to NHE undertaken either before (BT) or after (AT) simulated football training. Twelve amateur players performed six sets of five repetitions of the NHE either before or after 60 min of standardised football-specific exercise (SAFT60). Surface electromyography signals (EMG) of the hamstring muscles were recorded during both the NHE, and maximum eccentric actions of the knee flexors (0.52 rad · s-1) performed before and after the NHE programme, and at 15 min intervals during SAFT60. Ten-metre sprint times were recorded on three occasions during each 15 min SAFT60 segment. Greater eccentric hamstring fatigue following the NHE programme was observed in BT versus AT (19.8 %; very likely small effect), which was particularly apparent in the latter range of knee flexion (0-15°; 39.6%; likely moderate effect), and synonymous with hamstring EMG declines (likely small-likely moderate effects). Performing NHE BT attenuated sprint performance declines (2.0-3.2%; likely small effects), but decreased eccentric hamstring peak torque (-14.1 to -18.9%; likely small effects) during football-specific exercise. Performing NHE prior to football training reduces eccentric hamstring strength and may exacerbate hamstring injury risk.

Anticipatory and compensatory postural adjustments in people with low back pain: a protocol for a systematic review and meta-analysis.

BACKGROUND: Anticipatory (APAs) and compensatory (CPAs) postural adjustments are organised by the central nervous system (CNS) and serve to control postural perturbations. Ineffective APAs and CPAs have been hypothesised to contribute to the persistence of symptoms and disability in people with low back pain (LBP). Despite two decades of research, there is no systematic review investigating APAs and CPAs in people with LBP. Thus, the aim of the current review is to determine if APA and CPA onset or amplitude, as measured by electromyography (EMG), centre of pressure (COP), and kinematics, are altered in people with LBP. METHODS/DESIGN: A systematic review and meta-analysis will be conducted. Searches will be conducted in electronic databases for full-text articles published before January 2016 using pre-defined search strategies that utilise combinations of keywords and medical subject heading terms. Two independent reviewers will screen potentially relevant articles for inclusion, extract data, and assess risk of bias for individual studies. Any disagreements will be resolved by a third reviewer. Studies comparing APA onset and amplitude and CPA onset and amplitude measured by EMG, COP, or kinematics between people with LBP and healthy individuals will be included if all aspects of the eligibility criteria are met. Data will be synthesised if studies are homogeneous; otherwise, results will be reviewed narratively. DISCUSSION: To our knowledge, this is the first systematic review to examine APAs and CPAs, as measured by EMG, COP, and kinematics in people with LBP. The findings of this review may aid in the identification of factors that play a role in the persistence of symptoms and disability and aid in the development of interventions to treat symptoms. SYSTEMATIC REVIEW REGISTRATION: PROSPERO CRD42016032815.

The effect of resistance training on markers of immune function and inflammation in previously sedentary women recovering from breast cancer: a randomized controlled trial.

The purpose of this randomized controlled trial was to determine the effects of resistance training (RT) on markers of inflammation and immune function in breast cancer survivors. Thirty-nine breast cancer survivors were randomly assigned to a RT (n = 20) or control (n = 19) group. RT performed supervized exercise three times per week. Natural killer cell (NK) and natural killer T-cell (NKT) function, and markers of inflammation (serum TNF-α, IL-6, IL-10, and CRP) were measured before and after training. Changes in NK and NKT cell function were analyzed using ANCOVA, with the change score the dependent variable, and the baseline value of the same variable the covariate. Effect sizes (ES) were calculated via partial eta-squared. We found a significant reduction, and large associated ESs, in the RT group compared to the control group for change in NK cell expression of TNF-α (p = 0.005, ES = 0.21) and NKT cell expression of TNF-α (p = 0.04, ES = 0.12). No differences were observed in any serum marker. Significant improvements in all measurements of strength were found in RT compared to control (p < 0.001; large ESs ranging from 0.32 to 0.51). These data demonstrate that RT has a beneficial effect on the NK and NKT cell expression of TNF-α indicating that RT may be beneficial in improving the inflammatory profile in breast cancer survivors.

Passive heating following the prematch warm-up in soccer: examining the time-course of changes in muscle temperature and contractile function.

This study examined changes in muscle temperature, electrically evoked muscle contractile properties, and voluntary power before and after a soccer specific active warm-up and subsequent rest period. Ten amateur soccer players performed two experimental sessions that involved performance of a modified FIFA 11+ soccer specific warm-up, followed by a 12.5-min rest period where participants were required to wear either normal clothing or a passive electrical heating garment was applied to the upper thigh muscles. Assessments around the warm-up and cool-down included measures of maximal torque, rate of torque development, muscle temperature (Tm), and electrically evoked measures of quadriceps contractile function. Tm was increased after the warm-up by 3.2 ± 0.7°C (P < 0.001). Voluntary and evoked rates of torque development increased after the warm-up between 20% and 30% (P < 0.05), despite declines in both maximal voluntary torque and voluntary activation (P < 0.05). Application of a passive heating garment in the cool-down period after the warm-up did not effect variables measured. While Tm was reduced by 1.4 ± 0.4°C after the rest period (P < 0.001), this value was still higher than pre warm-up levels. Voluntary and evoked rate of torque development remained elevated from pre warm-up levels at the end of the cool-down (P < 0.05). The soccer specific warm-up elevated muscle temperature by 3.2°C and was associated with concomitant increases of between 20% and 30% in voluntary rate of torque development, which seems explained by elevations in rate-dependent measures of intrinsic muscle contractile function. Application of a passive heating garment did not attenuate declines in muscle temperature during a 12.5-min rest period.

The Magnitude of Peripheral Muscle Fatigue Induced by High and Low Intensity Single-Joint Exercise Does Not Lead to Central Motor Output Reductions in Resistance Trained Men.

PURPOSE: To examine quadriceps muscle fatigue and central motor output during fatiguing single joint exercise at 40% and 80% maximal torque output in resistance trained men. METHOD: Ten resistance trained men performed fatiguing isometric knee extensor exercise at 40% and 80% of maximal torque output. Maximal torque, rate of torque development, and measures of central motor output and peripheral muscle fatigue were recorded at two matched volumes of exercise, and after a final contraction performed to exhaustion. Central motor output was quantified from changes in voluntary activation, normalized surface electromyograms (EMG), and V-waves. Quadriceps muscle fatigue was assessed from changes in the size and shape of the resting potentiated twitch (Q.(pot.tw)). Central motor output during the exercise protocols was estimated from EMG and interpolated twitches applied during the task (VA(sub)). RESULTS: Greater reductions in maximal torque and rate of torque development were observed during the 40% protocol (p<0.05). Maximal central motor output did not change for either protocol. For the 40% protocol reductions from pre-exercise in rate and amplitude variables calculated from the Q.(pot.tw) between 66.2 to 70.8% (p<0.001) exceeded those observed during the 80% protocol (p<0.01). V-waves only declined during the 80% protocol between 56.8 ± 35.8% to 53.6 ± 37.4% (p<0.05). At the end of the final 80% contraction VA(sub) had increased from 91.2 ± 6.2% to 94.9 ± 4.7% (p = 0.005), but a greater increase was observed during the 40% contraction where VA(sub) had increased from 67.1 ± 6.1% to 88.9 ± 9.6% (p<0.001). CONCLUSION: Maximal central motor output in resistance trained men is well preserved despite varying levels of peripheral muscle fatigue. Upregulated central motor output during the 40% contraction protocol appeared to elicit greater peripheral fatigue. V-waves declines during the 80% protocol suggest intensity dependent modulation of the Ia afferent pathway.

Hamstring Fatigue and Muscle Activation Changes During Six Sets of Nordic Hamstring Exercise in Amateur Soccer Players.

The Nordic hamstring exercise (NHE) is a bodyweight movement commonly prescribed to increase eccentric hamstring strength and reduce the incidence of strain injury in sport. This study examined hamstring fatigue and muscle activation responses throughout 6 sets of 5 repetitions of the NHE. Ten amateur-level soccer players performed a single session of 6 sets of 5 repetitions of NHE. Maximal eccentric and concentric torque output (in newton meters) was measured after every set. Hamstrings electromyograms (EMG) were measured during all maximal contractions and exercise repetitions. Hamstring maximal eccentric torque was reduced throughout the range of motion after only a single set of NHE between 7.9 and 17.1% (p ≤ 0.05), with further reductions in subsequent sets. Similarly, maximal concentric torque reductions between 7.8 and 17.2% were observed throughout the range of motion after 1 set of NHE (p ≤ 0.05). During the descent phase of the NHE repetitions, hamstring muscle activity progressively increased as the number of sets performed increased. These increases were observed in the first half of the range of motion. During the ascent phase, biceps femoris muscle activity but not medial hamstrings was reduced from the start of exercise during latter sets of repetitions. These data provide unique insight into the extent of fatigue induced from a bodyweight only exercise after a single set of 5 repetitions. Strength and conditioning coaches need to be aware of the speed and extent of fatigue induced from NHE, particularly in practical settings in which this exercise is now prescribed before sport-specific training sessions (i.e., the FIFA-11 before soccer training).

Lower hamstring extensibility in men compared to women is explained by differences in stretch tolerance.

BACKGROUND: This study examined whether passive hamstring tissue stiffness and/or stretch tolerance explain the relationship between sex and hamstring extensibility. METHODS: Ninety healthy participants, 45 men and 45 women (mean ± SD; age 24.6 ± 5.9 years, height 1.72 ± 0.09 m, weight 74.6 ± 14.1 kg) volunteered for this study. The instrumented straight leg raise was used to determine hamstring extensibility and allow measurement of stiffness and stretch tolerance (visual analog pain score, VAS). RESULTS: Hamstring extensibility was 9.9° greater in women compared to men (p = 0.003). VAS scores were 16 mm lower in women (p = 0.001). Maximal stiffness (maximal applied torque) was not different between men and women (p = 0.42). Passive stiffness (slope from 20-50° hip flexion) was 0.09 Nm.°(-1) lower in women (p = 0.025). For women, linear and stepwise regression showed that no predictor variables were associated with hamstring extensibility (adjusted r(2) = -0.03, p = 0.61). For men, 44% of the variance in hamstring extensibility was explained by VAS and maximal applied torque (adjusted r(2) = 0.44, p < 0.001), with 41% of the model accounted for by the relationship between higher VAS scores and lower extensibility (standardized ß coefficient = -0.64, p < 0.001). CONCLUSIONS: The results of this study suggest that stretch tolerance and not passive stiffness explains hamstring extensibility, but this relationship is only manifest in men.

Hamstring muscle fatigue and central motor output during a simulated soccer match.

PURPOSE: To examine changes in hamstring muscle fatigue and central motor output during a 90-minute simulated soccer match, and the concomitant changes in hamstring maximal torque and rate of torque development. METHOD: Eight amateur male soccer players performed a 90-minute simulated soccer match, with measures performed at the start of and every 15-minutes during each half. Maximal torque (Nm) and rate of torque development (RTD; Nm.s-1) were calculated from maximal isometric knee flexor contractions performed at 10° of flexion. Hamstring peripheral fatigue was assessed from changes in the size and shape of the resting twitch (RT). Hamstring central motor output was quantified from voluntary activation (%) and normalized biceps femoris (BF) and medial hamstrings (MH) electromyographic amplitudes (EMG/M). RESULTS: Maximal torque was reduced at 45-minutes by 7.6±9.4% (p<0.05). RTD in time intervals of 0-25, 0-50, and 0-75 ms post-contraction onset were reduced after 15-minutes in the first-half between 29.6 to 46.2% (p<0.05), and were further reduced at the end of the second-half (p<0.05). Maximal EMG/M was reduced for biceps femoris only concomitant to the time-course of reductions in maximal torque (p = 0.007). The rate of EMG rise for BF and MH was reduced in early time periods (0-75 ms) post-contraction onset (p<0.05). No changes were observed for the size and shape of the RT, indicating no hamstring peripheral fatigue. CONCLUSION: Centrally mediated reductions in maximal torque and rate of torque development provide insight into factors that may explain hamstring injury risk during soccer. Of particular interest were early reductions during the first-half of hamstring rate of torque development, and the decline in maximal EMG/M of biceps femoris in the latter stages of the half. These are important findings that may help explain why the hamstrings are particularly vulnerable to strain injury during soccer.

Pain reported during prolonged standing is associated with reduced anticipatory postural adjustments of the deep abdominals.

Within the context of low back pain, the measurement of deep abdominal anticipatory postural adjustments (APAs) during rapid limb movement has received much interest. There is dispute about the association between APAs and back pain. Moreover, there is limited evidence examining compensatory postural adjustments (CPAs) in back pain. This study examined the relationship between APAs and CPAs with pain reported in the low back during 2 h of prolonged standing. Twenty-six participants with no history of severe back pain performed 2-h prolonged standing. APAs and CPAs of the deep abdominal muscles (transverse abdominis/internal obliques) were measured by surface electromyography during rapid shoulder flexion and extension. APAs and CPAs measured pre-standing revealed symmetrical anticipatory activity, but an asymmetry between the different sides of the abdominal wall for CPAs. APAs and CPAs measured pre-standing were not associated with pain reported during standing. For the whole group, APA amplitudes were reduced post-standing during shoulder flexion (p = 0.005). Pain reported during standing was associated with the changes in APA amplitudes post-standing (rs = 0.43, p = 0.002). These findings support previous research using hypertonic saline injections to induce back pain that showed reduced APA amplitudes, and extends findings to suggest pain does not effect compensatory postural adjustments.

Muscle activation does not increase after a fatigue plateau is reached during 8 sets of resistance exercise in trained individuals.

The premise of eliciting the greatest acute fatigue is accepted and used for designing programs that include excessive, potentially dangerous volumes of high-intensity resistance exercise. There is no evidence examining acute fatigue and neuromuscular responses throughout multiple sets of moderate-to-high intensity resistance exercise. Fifteen resistance-trained male subjects performed a single exercise session using 8 sets of Bulgarian split squats performed at 75% maximal force output. Maximal force output (N) was measured after every set of repetitions. Electromyographic (EMG) activity of vastus lateralis was monitored during all force trials and exercise repetitions. Repetitions per set decreased from the first to the third set (p < 0.001). Maximal force output decreased from preexercise to set 4 (p < 0.001). Electromyographic amplitudes during exercise did not change. Secondary subgroup analysis was performed based on the presence, or not, of a fatigue plateau (<5% reductions in maximal force output in subsequent sets). Nine participants exhibited a fatigue plateau, and 6 did not. Participants who plateaued performed less first-set repetitions, accrued less total volume, and did not exhibit increases in EMG amplitudes during exercise. Initial strength levels and neuromuscular demand of the exercise was the same between the subgroups. These data suggest that there are individual differences in the training session responses when prescribing based off a percentage of maximal strength. When plateaus in fatigue and repetitions per set are reached, subsequent sets are not likely to induce greater fatigue and muscle activation. High-volume resistance exercise should be carefully prescribed on an individual basis, with intrasession technique and training responsiveness continually monitored.