The Neuromuscular Fatigue-Induced Loss of Muscle Force Control

Neuromuscular fatigue is characterised not only by a reduction in the capacity to generate maximal muscle force, but also in the ability to control submaximal muscle forces, i.e., to generate task-relevant and precise levels of force. This decreased ability to control force is quantified according to a greater magnitude and lower complexity (temporal structure) of force fluctuations, which are indicative of decreased force steadiness and adaptability, respectively. The “loss of force control” is affected by the type of muscle contraction used in the fatiguing exercise, potentially differing between typical laboratory tests of fatigue (e.g., isometric contractions) and the contractions typical of everyday and sporting movements (e.g., dynamic concentric and eccentric contractions), and can be attenuated through the use of ergogenic aids. The loss of force control appears to relate to a fatigue-induced increase in common synaptic input to muscle, though the extent to which various mechanisms (afferent feedback, neuromodulatory pathways, cortical/reticulospinal pathways) contribute to this remains to be determined. Importantly, this fatigue-induced loss of force control could have important implications for task performance, as force control is correlated with performance in a range of tasks that are associated with activities of daily living, occupational duties, and sporting performance

Exercise-induced muscle damage is reduced in resistance-trained males by branched chain amino acids: a randomized, double-blind, placebo controlled study

Background: It is well documented that exercise-induced muscle damage (EIMD) decreases muscle function and causes soreness and discomfort. Branched-chain amino acid (BCAA) supplementation has been shown to increase protein synthesis and decrease muscle protein breakdown, however, the effects of BCAAs on recovery from damaging resistance training are unclear. Therefore, the aim of this study was to examine the effects of a BCAA supplementation on markers of muscle damage elicited via a sport specific bout of damaging exercise in trained volunteers. Methods: Twelve males (mean ± SD age, 23 ± 2 y; stature, 178.3 ± 3.6 cm and body mass, 79.6 ± 8.4 kg) were randomly assigned to a supplement (n = 6) or placebo (n = 6) group. The damaging exercise consisted of 100 consecutive drop-jumps. Creatine kinase (CK), maximal voluntary contraction (MVC), muscle soreness (DOMS), vertical jump (VJ), thigh circumference (TC) and calf circumference (CC) were measured as markers of muscle damage. All variables were measured immediately before the damaging exercise and at 24, 48, 72 and 96 h post-exercise. Results: A significant time effect was seen for all variables. There were significant group effects showing a reduction in CK efflux and muscle soreness in the BCAA group compared to the placebo (P < 0.05). Furthermore, the recovery of MVC was greater in the BCAA group (P < 0.05). The VJ, TC and CC were not different between groups. Conclusion: The present study has shown that BCAA administered before and following damaging resistance exercise reduces indices of muscle damage and accelerates recovery in resistance-trained males. It seems likely that BCAA provided greater bioavailablity of substrate to improve protein synthesis and thereby the extent of secondary muscle damage associated with strenuous resistance exercise. Clinical Trial Registration Number: NCT01529281

Sprint Acceleration Mechanical Profiling of International Cricketers

Sprinting and speed is a fundamental skill and physical attribute crucial in seam bowlers and batters within cricket. The aim of this study was to assess differences in mechanical properties during sprinting between youth and senior international cricketers and between seam bowlers and batters. Retrospective 40m sprint times and anthropometric measures of 56 international cricketers (19 senior seam bowlers, 7 under-19 seam bowlers, 16 senior batters, 14 under-19 batters) were used to calculate the theoretical maximal force (F0), theoretical maximal velocity (V(0)), theoretical maximal power (Pmax), slope of the force-velocity relationship (F-V slope), maximal ratio of horizontal-to resultant force (RFmax), decrease in the ratio of horizontal-to-resultant force (DRF) and optimum velocity (Vopt). There were no significant (P > 0.05) differences in sprint times nor sprint mechanical profile variables between position or age. However, there was a moderately greater F0 (N/Kg) (ES = 0.78; 90% CI 0.19 - 1.34) and RFmax (ES = 0.75; 90% CI 0.11 - 1.35) in senior seam bowlers when compared to batters. Furthermore, FV Slope (ES = 0.79; 90% CI 0.15 - 1.40) and DRF (ES = 0.75; 90% CI 0.11 - 1.35) were moderately greater in senior compared to under-19 batters. When expressed relative to body mass, it appears that senior international seam bowlers show trends towards a more force biased profile during sprinting when compared to batters. These findings will help coaches to optimise physical preparation strategies in youth and senior international cricketers

The effect of combined isometric and plyometric training on musculotendinous ankle stiffness and its subsequent effect on performance in international age-group track sprint cycling

Within sprint cycling, the ankle’s primary role is transferring power generated at the hip and knee. However, a stiffer musculotendinous unit around the ankle may directly contribute to increased performance. The aim of this study was to measure the influence of isometric and plyometric training on ankle stiffness and sprint cycling performance. Fifteen international age-group sprint track cyclists completed a 10-week intervention. An experimental group (n = 8) performed high-volume plyometrics and isometric calf raises in addition to their normal training, whilst a control group (n = 7) continued with no intervention. Kinetic measures were recorded on a force plate and in sprints on an isokinetic ergometer at 60 and 135 rev/min. Kinematic measures were recorded using highspeed cameras and reflective markers. Isometric peak force during plantar flexion and vertical ankle stiffness when hopping were both increased in the intervention group (p ≤ 0.05). Bicycle sprints showed group differences in ankle stiffness (p = 0.01) at 135 rev/min and average ankle angle (p = 0.04) at 60 rev/min. Therefore, combined plyometrics and isometrics were an effective method for increasing ankle stiffness. This combination of stimuli also effected the utilisation of the ankle in sprint cycling

Enhanced Corticospinal Excitability and Volitional Drive in Response to Shortening and Lengthening Strength Training and Changes Following Detraining

There is a limited understanding of the neurological adaptations responsible for changes in strength following shortening and lengthening resistance training and subsequent detraining. The aim of the study was to investigate differences in corticospinal and spinal responses to resistance training of the tibialis anterior muscle between shortening or lengthening muscle contractions for 4 weeks and after 2 weeks of detraining. Thirty-one untrained individuals were assigned to either shortening or lengthening isokinetic resistance training (4 weeks, 3 days/weeks) or a non-training control group. Transcranial magnetic stimulation and peripheral nerve stimulation (PNS) were used to assess corticospinal and spinal changes, respectively, at pre-, mid-, post-resistance training and post detraining. Greater increases changes (P 0.05), although MEP amplitude decreased during the detraining period (P < 0.01). No changes in H-reflex were found pre to post resistance training or post detraining. Modulation in V-wave appeared to be contraction specific, whereby greatest increases occurred following lengthening resistance training. Strength and volitional drive is maintained following 2 weeks detraining, however corticospinal excitability appears to decrease when the training stimulus is withdrawn

Physiological and perceptual responses to a five-week pre-event taper in professional mixed martial arts athletes

BACKGROUNDː The purpose of this study was to evaluate changes in markers of endocrine, immune and mood status among Mixed Martial Arts (MMA) athletes during different stages of fight preparation camps. METHODSː Six professional MMA athletes were observed across the final five weeks (W4 – W0); including the final seven days (D6 – D0) of fight camp, and were tested for salivary immunoglobin-A (sIgA), salivary cortisol (SC), creatine kinase (CK), urine osmolality (UO), body mass (BM), training load (TL), reported fluid intake and profile of mood state (POMS) scores. RESULTSː Magnitude-based decisions revealed large, very likely decreases in sIgA concentrations in W1 relative to all previous weeks, and large, very likely reductions in CK concentrations within W0 in relation to W2 and W4. POMS scores were reduced in W0 and W1 compared to W4 (moderate, very likely), despite a reduction in training load in W0 relative to all previous weeks (large, very likely). In W0, reported fluid intake decreased as UO increased at D1 and D2, in comparison to all previous days (large, very likely). Elevated POMS and SC (moderate to large, very likely) were also observed at D1, in comparison to D2 to D6. While 8% of BM was lost over the 5-week period, 5% was lost within the final 4 days. CONCLUSIONSː Across a 5-week fight camp, mood states are negatively affected, alongside increased markers of muscle damage and immune status, which can be partially offset with a pre-event taper. Owing to the weight cutting practices of these professional MMA athletes, ~ 5% of BM is lost in the final 4 days, which coincides with poorer mood states and increased stress-hormone responses in the final few days of the fight camp. Coaches should consider the implications of taper length and RWL strategies in the recovery process of MMA athletes

Field-based and overspeed potentiated warm-ups increase clubhead speed and drive carry distance in skilled collegiate golfers

Warm-ups utilising post-activation performance enhancement (PAPE) strategies have been shown to increase clubhead speed (CHS) in golfers. However, the effectiveness of overspeed training using weighted clubs to elicit PAPE in CHS is unknown. The purpose of this investigation was to compare traditional, field-based warm-up activities with no potentiation activity (CON), against a field-based potentiated warm-up using high rate of force development bodyweight movements (BWP), and an overspeed warm-up using speed sticks (SSP) as the potentiation method. Thirteen skilled adult male golfers (handicap 1.0 ± 2.1) completed three testing sessions, separated by seven days. The CON, BWP and SSP warm-ups were identical, except for the potentiation method. After each warm-up condition, ten shots, separated by one minute, were recorded using a doppler rader launch monitor (Trackman 4) with CHS, ball speed (BS), carry distance (CD) and total distance (TD) recorded. A repeated measures one-way ANOVA with Bonferroni post hoc pairwise comparisons revealed increases in CHS in the BWP (p= 0.004) and SSP (p= 0.003) groups against CON, with no difference between BWP and SSP. Increased CD was observed for BWP (p= 0.034) and SWP (p= 0.030) against CON with no differences between BWP and SSP. No differences for BS or TD were observed. Warm-ups with BWP or SSP activities should be considered if players are attempting to increase CHS or CD of drives, although utilising overspeed potentiation methods appear to confer no additional benefit to bodyweight PAPE exercises in skilled collegiate golfers

Physiological and thermoregulatory effects of oral taurine supplementation on exercise tolerance during forced convective cooling

We investigated the effects of taurine supplementation on cycling time to exhaustion in cold conditions. Eleven males cycled to exhaustion at a power output equivalent to the mid-point between ventilatory threshold and maximum aerobic power following 15-min rest in the cold (apparent temperature of ∼ 4 °C; air flow of 4.17 m·s-1). Two-hours before, participants ingested taurine (50 mg·kg-1) or placebo beverage. Pulmonary gases, carbohydrate (CHO) and fat oxidation, body temperatures, mean local sweat rate, heart rate, rate of perceived exertion (RPE) and thermal comfort were recorded. Time to exhaustion was not different between trials (taurine = 14.6 ± 4.7 min; placebo = 13.4 ± 5.6 min, P = 0.061, d = 0.27). There were no effects (P > 0.05) of taurine on core temperature, mean skin temperature or local sweat rates. However, the placebo condition showed greater (P < 0.05) reductions in arm-to-finger temperature gradient (i.e. vasodilation) across pre-exercise passive cold exposure and increased CHO oxidation (P < 0.05). Participants also reached a thermally ‘comfortable’ level quicker in the taurine condition (P < 0.05). A 50 mg·kg-1 dose of taurine did not statistically benefit endurance exercise after moderate cold exposure but conferred some potential vascular and metabolic effects

Effects of Heat Acclimation and Acclimatisation on Maximal Aerobic Capacity Compared to Exercise Alone in Both Thermoneutral and Hot Environments: A Meta-Analysis and Meta-Regression

BackgroundHeat acclimation and acclimatisation (HA) is typically used to enhance tolerance to the heat, thereby improving performance. HA might also confer a positive adaptation to maximal oxygen consumption (VO2max), although this has been historically debated and requires clarification via meta-analysis.Objectives(1) To meta-analyse all studies (with and without control groups) that have investigated the effect of HA on VO2max adaptation in thermoneutral or hot environments; (2) Conduct meta-regressions to establish the moderating effect of selected variables on VO2max adaptation following HA.MethodsA search was performed using various databases in May 2020. The studies were screened using search criteria for eligibility. Twenty-eight peer-reviewed articles were identified for inclusion across four separate meta-analyses: (1) Thermoneutral VO2max within-participants (pre-to-post HA); (2) Hot VO2max within-participants (pre-to-post HA); (3) Thermoneutral VO2max measurement; HA vs. control groups; (4) Hot VO2max measurement, HA vs. control groups. Meta-regressions were performed for each meta-analysis based on: isothermal vs. iso-intensity programmes, days of heat exposure, HA ambient temperature (°C), heat index, HA session duration (min), ambient thermal load (HA session x ambient temperature), mean mechanical intensity (W) and the post-HA testing period (days).ResultsThe meta-analysis of pre–post differences in thermoneutral VO2max demonstrated small-to-moderate improvements in VO2max (Hedges’ g = 0.42, 95% CI 0.24–0.59, P < 0.001), whereas moderate improvements were found for the equivalent analysis of hot VO2max changes (Hedges’ g = 0.63, 95% CI 0.26–1.00, P < 0.001), which were positively moderated by the number of days post-testing (P = 0.033, β = 0.172). Meta-analysis of control vs. HA thermoneutral VO2max demonstrated a small improvement in VO2max in HA compared to control (Hedges’ g = 0.30, 95% CI 0.06–0.54, P = 0.014) and this effect was larger for the equivalent hot VO2max analysis where a higher (moderate-to-large) improvement in VO2max was found (Hedges’ g = 0.75, 95% CI 0.22–1.27, P = 0.005), with the number of HA days (P = 0.018; β = 0.291) and the ambient temperature during HA (P = 0.003; β = 0.650) positively moderating this effect.ConclusionHA can enhance VO2max adaptation in thermoneutral or hot environments, with or without control group consideration, by at least a small and up to a moderate–large amount, with the larger improvements occurring in the heat. Ambient heat, number of induction days and post-testing days can explain some of the changes in hot VO2max adaptation

Reliability and validity of velocity measures and regression methods to predict maximal strength ability in the back-squat using a novel linear position transducer.

Purpose: to examine the reliability of load-velocity profiles (LVPs) and validity of 1-repetition maximum (1-RM) prediction methods in the back-squat using the novel Vitruve linear position transducer (LPT). Methods: twenty-five men completed a back-squat 1-RM assessment followed by 2 LVP trials using 5 incremental loads (20%-40%-60%-80%-90% 1-RM). Mean propulsive velocity (MPV), mean velocity (MV), and peak velocity (PV) were measured via a (LPT). Linear and polynomial regression models were applied to the data. The reliability and validity criteria were defined a-priori as intraclass correlation coefficient (ICC) or Pearson correlation coefficient (r) > 0.70, coefficient of variation (CV) ≤ 10%, and effect size (ES) < 0.60. Bland-Altman analysis and heteroscedasticity of errors (r2) were also assessed. Results: the main findings indicated MPV, MV and PV were reliable across 20- 13 90% 1-RM (CV < 8.8%). The secondary findings inferred all prediction models had acceptable reliability (CV < 8.0%). While the MPV linear and MV linear models demonstrated the best estimation of 1-RM (CV < 5.9%), all prediction models displayed unacceptable validity and a tendency to overestimate or underestimate 1-RM. Mean systematic bias (-7.29 to 2.83 kg) was detected for all prediction models, along with little to no heteroscedasticity of errors for linear (r2 < 0.04) and polynomial models (r2 < 0.08). Furthermore, all 1-RM estimations were significantly different from each other (p < 0.03). Conclusions: MPV, MV, and PV can provide reliable LVPs and repeatable 1-RM predictions. However, prediction methods may not be sensitive enough to replace direct assessment of 1-RM. Polynomial regression is not suitable for 1-RM prediction