High-threshold motor unit firing reflects force recovery following a bout of damaging eccentric exercise

Exercise-induced muscle damage (EIMD) is associated with impaired muscle function and reduced neuromuscular recruitment. However, motor unit firing behaviour throughout the recovery period is unclear. EIMD impairment of maximal voluntary force (MVC) will, in part, be caused by reduced high-threshold motor unit firing, which will subsequently increase to recover MVC. Fourteen healthy active males completed a bout of eccentric exercise on the knee extensors, with measurements of MVC, rate of torque development and surface electromyography performed pre-exercise and 2, 3, 7 and 14 days post-exercise, on both damaged and control limb. EIMD was associated with decreased MVC (235.2 ± 49.3 Nm vs. 161.3 ± 52.5 Nm; p < 0.001) and rate of torque development (495.7 ± 136.9 Nm.s-1 vs. 163.4 ± 163.7 Nm.s-1; p < 0.001) 48h post-exercise. Mean motor unit firing rate was reduced (16.4 ± 2.2 Hz vs. 12.6 ± 1.7 Hz; p < 0.01) in high-threshold motor units only, 48h post-exercise, and common drive was elevated (0.36 ± 0.027 vs. 0.56 ± 0.032; p < 0.001) 48h post-exercise. The firing rate of high-threshold motor units was reduced in parallel with impaired muscle function, whilst early recruited motor units remained unaltered. Common drive of motor units increased in offset to the firing rate impairment. These alterations correlated with the recovery of force decrement, but not of pain elevation. This study provides fresh insight into the central mechanisms associated with EIMD recovery, relative to muscle function. These findings may in turn lead to development of novel management and preventative procedures

The Effect of Foam Rolling for Three Consecutive Days on Muscular Efficiency and Range of Motion

Background Foam rolling (FR) has been shown to alleviate some symptoms of exercise-induced muscle damage and has been suggested to increase range of motion (ROM) without negatively impacting strength. However, it is unclear what neuromuscular effects, if any, mediate these changes. Methods In a randomized, crossover design, 16 healthy active males completed 2 min of rest or FR of the knee extensors on three consecutive days. Mechanical properties of vastus lateralis (VL) and rectus femoris (RF) were assessed via Tensiomyography. Knee extension maximal voluntary contraction (MVC) and knee flexion ROM were also assessed, and surface electromyography amplitude (RMS) was recorded during a submaximal isometric contraction (50% of MVC). Measures were performed before and after (0, 15, and 30 min) FR or rest. Results MVC was reduced on subsequent days in the rest condition compared to FR (p = 0.002, pη2 = 0.04); ROM was not different across time or condition (p = 0.193, pη2 = 0.01). Stiffness characteristics of the VL were different on the third day of FR (p = 0.002, pη2 = 0.03). RMS was statistically reduced 0, 15, and 30 min after FR compared to rest (p = 0.006, pη2 = 0.03; p = 0.003, pη2 = 0.04; p = 0.002, pη2 = 0.04). Conclusions Following FR, MVC was elevated compared to rest and RMS was transiently reduced during a submaximal task. Excitation efficiency of the involved muscles may have been enhanced by FR, which protected against the decline in MVC which was observed with rest

Reduced Radial Displacement of the Gastrocnemius Medialis Muscle After Electrically Elicited Fatigue

Context:&nbsp;Assessments of skeletal muscle functional capacity often necessitate maximal contractile effort, which exacerbates muscle fatigue or injury. Tensiomyography (TMG) has been investigated as a means to assess muscle contractile function following fatigue; however observations have not been contextualised by concurrent physiological measures. Objective:&nbsp;The aim of the present investigation was to measure peripheral fatigue-induced alterations in mechanical and contractile properties of the plantar flexor muscles through non-invasive TMG concurrently with maximal voluntary contraction (MVC) and passive muscle tension (PMT) in order to validate TMG as a gauge of peripheral fatigue. Design:&nbsp;Pre- and post-test intervention with control. Setting:&nbsp;University laboratory. Participants:&nbsp;Twenty-one healthy male volunteers. Interventions:&nbsp;Subjects plantar flexors were tested for TMG parameters, along with MVC and PMT, before and after either a 5 minute rest period (control) or a 5 minute electrical stimulation intervention (fatigue). Main Outcome Measures:&nbsp;Temporal (contraction velocity) and spatial (radial displacement) contractile parameters of the Gastrocnemius Medialis were recorded through TMG. MVC was measured as an indicator of muscle fatigue and PMT was measured to assess muscle stiffness. Results:&nbsp;Radial displacement demonstrated a fatigue-associated reduction (3.3 &plusmn; 1.2 vs. 4.0 &plusmn; 1.4 mm vs, p=0.031), while contraction velocity remained unaltered. Additionally, MVC significantly declined by 122.6 &plusmn; 104 N (p&lt;0.001) following stimulation (fatigue). PMT was significantly increased following fatigue (139.8 &plusmn; 54.3 vs. 111.3 &plusmn; 44.6 N, p=0.007).&nbsp; Conclusion: TMG successfully detected fatigue, evident from reduced MVC, by displaying impaired muscle displacement, accompanied by elevated PMT. TMG could be useful in establishing fatigue status of skeletal muscle without exacerbating the functional decrement of the muscle

The match between what is prescribed and reasons for prescribing in exercise referral schemes:a mixed method study

Background: Exercise referral schemes (ERS) aim to tackle non-communicable disease (NCD) by increasing physical activity levels through prescribed exercise. However, there is a sparsity of knowledge upon what exercises are prescribed and if they are targeted towards tackling NCD. Method: Mixed methods were employed. Quantitative data was extracted from exercise prescription cards of 50 participants and were assessed for frequency, intensity, type and time of prescribed exercise. Descriptive measures of aggregate data are expressed as median (range: minimum-maximum). Thematic analysis of semi-structured interviews generated qualitative data on exercise referral instructors’ experiences of prescribing exercise. Results: Thirty-eight different types of exercise were prescribed. Median prescription was 4 (1–11) exercises per session, at a moderate intensity. Participants were prescribed a median of 35 (5–70) minutes of aerobic exercise per referral session. Exercise referral instructors prescribed exercise to improve activities of daily living, promote independence and autonomy of participants, rather than explicitly targeting the referral condition. Conclusions: Knowledge that prescribed exercises are not explicitly targeted to the referral condition provides critical information in understanding the purpose of exercise prescription. Future evaluations of ERS should be mindful of this, that is, perceived outcomes might not match up to what is being prescribed within ERS.</p

Exercise Referral Instructors’ Perspectives on Supporting and Motivating Participants to Uptake, Attend and Adhere to Exercise Prescription:A Qualitative Study

Exercise referral schemes are designed to support people with non-communicable diseases to increase their levels of exercise to improve health. However, uptake and attendance are low. This exploratory qualitative study aims to understand uptake and attendance from the perspectives of exercise referral instructors using semi-structured interviews. Six exercise referral instructors from one exercise referral scheme across four exercise referral sites were interviewed. Four themes emerged: (i) the role that instructors perceive they have and approaches instructors take to motivate participants to take-up, attend exercise referral and adhere to their exercise prescription; (ii) instructors’ use of different techniques, which could help elicit behaviour change; (iii) instructors’ perceptions of participants’ views of exercise referral schemes; and (iv) barriers towards providing an exercise referral scheme. Exercise referral instructors play an important, multifaceted role in the uptake, attendance and adherence to exercise referral. On-going education and peer support for instructors may be useful. Instructors’ perspectives help us to further understand how health and leisure services can design successful exercise referral schemes.</p

Understanding the consequences of repetitive subconcussive head impacts in sport : brain changes and dampened motor control are seen after boxing practice

LW was supported by FP7 grant number 602150-2 (CENTER-TBI)Objectives: The potential effects of exposure to repetitive subconcussive head impacts through routine participation in sport are not understood. To investigate the effects of repetitive subconcussive head impacts we studied boxers following customary training (sparring) using transcranial magnetic stimulation (TMS), decomposition electromyographic (EMG) and tests of memory. Methods: Twenty amateur boxers performed three 3-min sparring bouts. Parameters of brain function and motor control were assessed prior to sparring and again immediately, 1 h and 24 h post-sparring. Twenty control participants were assessed following mock-sparring. Results: One hour after sparring boxers showed increased corticomotor inhibition, altered motor unit recruitment strategies, and decreased memory performance relative to controls, with values returning to baseline by the 24 h follow up. Conclusion: Repetitive subconcussive head impacts associated with sparring resulted in acute and transient brain changes similar to those previously reported in soccer heading, providing convergent evidence that sport-related head impacts produce a GABAergic response. These acute changes in brain health are reminiscent of effects seen following brain injury, and suggest a potential mechanism underlying the damaging long-term effects of routine repetitive head impacts in sport.Publisher PDFPeer reviewe

Reliability of Change of Direction and Agility Assessments in Youth Soccer Players

Considering the vast physical and neural developments experienced throughout adolescence, the reliability of physical performance may vary in youth populations. This study aimed to examine the reliability of change of direction (COD) and agility tests in youth soccer players. Altogether, 86 youth soccer players, aged 13.6 ± 2.0 years, volunteered to participate. Data were collected from a modified 505 COD test (m505COD) and the Y-sprint drill in both pre-planned (Y-SprintPRE) and reactive (Y-SprintREACT) conditions during 2 sessions, 7 days apart. Anthropometric data including body mass, standing stature, and sitting height were also collected. COD and agility tests demonstrated good reliability (ICC = 0.81–0.91; CV = 1.2–2.0; d = 0.00–0.31; p < 0.01) for our entire sample. However, we observed a small negative relationship between age and intersession differences for the Y-SprintPRE (r = −0.28; p = 0.04), and moderate negative relationships between both age (r = −0.41; p < 0.01), and maturity offset (r = −0.39; p < 0.01) for the Y-SprintREACT. Although the COD and agility tests adopted within this study possess good intersession reliability, we observed greater intersession differences for younger and less mature individuals. We suggest that while COD and agility tests may provide meaningful objective data for monitoring the development of youth soccer players, these tests should be used with caution when evaluating younger, more immature athletes

Dryland Performance Tests Are Not Good Predictors of World Aquatics Points in Elite Male and Female Swimmers

Swim performance can be reliant on strength and power. Standardisation of swim performance in different events, distances, and sexes can be completed using World Aquatics points, allowing for ranking of swimmers. The aim of this retrospective cross-sectional study was to assess whether relationships between World Aquatics points and dryland markers of performance existed in male and female elite swimmers separately and combined. Methods: Dryland tests included Optojump® photoelectric cell countermovement jump, countermovement jump reach with a Vertec® system, standing broad jump using a tape measure, repetition maximum testing in the barbell back squat, barbell deadlift, and barbell bench press. Swim performance data and dryland test data onelite male (n = 38) and female (n = 20) Scottish swimmers from 2009–2017 were collected. Swim performance data were converted to World Aquatics federation points, and Bayesian linear regression analyses examined relationships between World Aquatics points and dryland performance tests:countermovement jump height (cm) using an Optojump® photoelectric cells system, countermove ment jump height (cm) using a Vertec® device, standing broad jump distance (cm), relative strength(load lifted (kg) per kg of body mass) in the barbell bench press (kg/kg), barbell back squat (kg/kg), barbell deadlift (kg/kg). Results: The Bayesian estimates of change of World Aquatics points for a unit change in jump-based measures were: Optojump®—men = 0.6, women = 0.6, combined = 0.4; Vertec®—men = 4.3, women = −1.6, combined = 2.4; standing broad jump—men = 0, women = −0, combined = 0.4. Strength-based measures were: barbell back squat—men = 2.3, women = 22, combined = −2.5; barbell deadlift—men = −5; barbell bench press—men = 41.8. Conclusions: Dryland performance tests are not good predictors of World Aquatics points and should rather be used for assessing training quality and monitoring injury risks

Effect of lower limb massage on electromyography and force production of the knee extensors

Objective: To evaluate the effect of massage on force production and neuromuscular recruitment. Methods: Ten healthy male subjects performed isokinetic concentric contractions on the knee extensors at speeds of 60, 120, 180, and 240&deg;/s. These contractions were performed before and after a 30 minute intervention of either rest in the supine position or lower limb massage. Electromyography (EMG) and force data were captured during the contractions. Results: The change in isokinetic mean force due to the intervention showed a significant decrease (p&lt;0.05) at 60&deg;/s and a trend for a decrease (p  =  0.08) at 120&deg;/s as a result of massage compared with passive rest. However, there were no corresponding differences in any of the EMG data. A reduction in force production was shown at 60&deg;/s with no corresponding alteration in neuromuscular activity. Conclusions: The results suggests that motor unit recruitment and muscle fibre conduction velocity are not responsible for the observed reductions in force. Although experimental confirmation is necessary, a possible explanation is that massage induced force loss by influencing &ldquo;muscle architecture&rdquo;. However, it is possible that the differences were only found at 60&deg;/s because it was the first contraction after massage. Therefore muscle tension and architecture after massage and the duration of any massage effect need to be examined

Longer Neurophysiological vs. Clinical Recovery Following Sport Concussion

Objectives: The objective of this study was to assess if injury-related alterations in the Sport Concussion Assessment Tool-5 (SCAT5) are matched by changes in transcranial magnetic stimulation-derived intracortical inhibition. We hypothesised that neurophysiological measures would take longer to return to normal than recovery assessed by the SCAT5 following sport related concussion (SRC). Methods: Thirteen male contact sport athletes (20.5 ± 4.5 years), who reported a concussion were recruited from local Rugby and American football clubs. Participants were tested at 4 timepoints throughout the concussion recovery period: within 24 h of concussion (day 0), and at 7, 9, and 11 days after concussion. All participants completed the SCAT5 and underwent TMS to assess cortical silent period duration (CSp), a measure of intracortical inhibition. Results: After concussion CSp significantly declined from day 0 (122 ± 28 ms) to day 11 (106 ± 15 ms) [F(3, 33) = 7.80, p < 0.001]. SCAT5 measures of symptom number and severity were significantly decreased [symptom number: χ2(3) = 30.44, p < 0.01; symptom severity: χ2(3) = 25.75, p < 0.001] between the day 0 timepoint and each of the other timepoints. SCAT5 balance errors (mBESS) decreased significantly [F(3, 33) = 19.55, p < 0.001] between the day 0 timepoint and each of the other timepoints. CSp and SCAT5 recovery patterns were different. SCAT5 domains recovered faster showing no further significant changes after day 7, whilst CSp was still decreasing between days 7 and 9. Due to the small sample size we also used a Bayesian linear model to investigate the recovery of CSp and mBESS. The posterior distribution of our Bayesian model provided evidence that CSp decreased at day 7 and it continued to decrease at day 9, unlike mBESS which decreased at day 7 and then reached a plateau. Conclusion: There are clinically important discrepancies between clinical and neurophysiological measures of concussion recovery. This finding has important implications for return to play (RTP) protocols and the prevention of complications after sport concussion