Voluntary activation of human knee extensors measured using transcranial magnetic stimulation

The aim of this study was to determine the applicability and reliability of a transcranial magnetic stimulation twitch interpolation technique for measuring voluntary activation of a lower limb muscle group. Cortical voluntary activation of the knee extensors was determined in nine healthy men on two separate visits by measuring superimposed twitch torques evoked by transcranial magnetic stimulation during isometric knee extensions of varying intensity. Superimposed twitch amplitude decreased linearly with increasing voluntary torque between 50 and 100% of mean maximal torque, allowing estimation of resting twitch amplitude and subsequent calculation of voluntary activation. There were no systematic differences for maximal voluntary activation within day (mean ± S.D. 90.9 ± 6.2 versus 90.7 ± 5.9%; P = 0.98) or between days (90.8 ± 6.0 versus 91.2 ± 5.7%; P = 0.92). Systematic bias and random error components of the 95% limits of agreement were 0.23 and 9.3% within day versus −0.38 and 7.5% between days. Voluntary activation was also determined immediately after a 2 min maximal voluntary isometric contraction; in four of these subjects, voluntary activation was determined 30 min after the sustained contraction. Immediately after the sustained isometric contraction, maximal voluntary activation was reduced from 91.2 ± 5.7 to 74.2 ± 12.0% (P < 0.001), indicating supraspinal fatigue. After 30 min, voluntary activation had recovered to 85.4 ± 8.8% (P = 0.39 versus baseline). These results demonstrate that transcranial magnetic stimulation enables reliable measurement of maximal voluntary activation and assessment of supraspinal fatigue of the knee extensors

The 2010 regulations on golf groove design: impact on ball flight characteristics during a controlled shot.

The purpose of this study was to investigate the difference in the amount of spin that can be generated during a controlled golf shot, as a result of the 2010 rule change regarding restrictions applied to the design of the grooves on the clubface implemented by the United States Golf Association and the Royal & Ancient Golf Club. Ten experienced golfers (mean ± SD; age, 23.0 ± 0.67 yr; playing experience, 13.2 ± 1.6 yr; handicap, 1.6 ± 1.4) were required to play a total of 120 shots inside a state of the art golf simulator with 3 clubs consisting of ‘old’ pre 2010 U-groove design and ‘new’ post 2010 V-groove design. With the U and V grooved clubs, participants played 10 shots from a fairway mat and 10 shots from a rough mat using a 9 iron, PW and SW. Backspin (RPM) and, as a measure of accuracy, distance landed from the pin (yds) were recorded. Compared to the U-grooves, the newer V-groove design imparted significantly less backspin from both the fairway and rough surfaces (P < 0.05), additionally, shots with all clubs were consistently further away from the pin (P < 0.05). The newer groove design does not enable players to impart as much backspin on the ball as they previously could and our data suggest that the recent change in golf club design might therefore reward driving accuracy

Central and peripheral determinants of fatigue in acute hypoxia

This thesis was submitted for the degree of Docter of Philosophy and awarded by Brunel University on 24th March 2011.Fatigue is defined as an exercise-induced decrease in maximal voluntary force produced by a muscle. Fatigue may arise from central and/or peripheral mechanisms. Supraspinal fatigue (a component of central fatigue) is defined as a suboptimal output from the motor cortex and measured using transcranial magnetic stimulation (TMS). Reductions in O2 supply (hypoxia) exacerbate fatigue and as the severity of hypoxia increases, central mechanisms of fatigue are thought to contribute more to exercise intolerance. In study 1, the feasibility of TMS to measure cortical voluntary activation and supraspinal fatigue of human knee-extensors was determined. TMS produced reliable measurements of cortical voluntary activation within- and between-days, and enabled the assessment of supraspinal fatigue. In study 2, the mechanisms of fatigue during single-limb exercise in normoxia (arterial O2 saturation [SaO2] ~98%), and mild to severe hypoxia (SaO2 93-80%) were determined. Hypoxia did not alter neuromuscular function or cortical voluntary activation of the knee-extensors at rest, despite large reductions in cerebral oxygenation. Maximal force declined by ~30% after single-limb exercise in all conditions, despite reduced exercise time in severe-hypoxia compared to normoxia (15.9 ± 5.4 vs. 24.7 ± 5.5 min; p < 0.05). Peripheral mechanisms of fatigue contributed more to the reduction in force generating capacity of the knee-extensors following single-limb exercise in normoxia and mild- to moderate-hypoxia, whereas supraspinal fatigue played a greater role in severe-hypoxia. In study 3, the effect of constant-load cycling exercise to the limit of tolerance in hypoxia (SaO2 ~80%) and normoxia was investigated. Time to the limit of tolerance was significantly shorter in hypoxia compared to normoxia (3.6 ± 1.3 vs. 8.1 ± 2.9 min; p < 0.001). The reductions in maximal voluntary force and knee-extensor twitch force at task-failure were not different in hypoxia compared to normoxia. However, the level of supraspinal fatigue was exacerbated in hypoxia, and occurred in parallel with reductions in cerebral oxygenation and O2 delivery. Supraspinal fatigue contributes to the decrease in whole-body exercise tolerance in hypoxia, presumably as a consequence of inadequate O2 delivery to the brain

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

The effect of hot and cold drinks on thermoregulation, perception and performance: the role of the gut in thermoreception

Purpose. Hot compared to cold drinks alter sweating responses during very low intensity exercise in temperate conditions. The thermoregulatory, perceptual and performance effects of hot compared to cold drinks in hot, dry conditions during high-intensity exercise have not been examined. Method. Ten participants (mean ± SD characteristics age 25 ± 5 years, height 1.81 ± 0.07 m, body mass 73.5 ± 10.6 kg, maximal power output (PMax) 350 ± 41 W). completed two conditions where they drank four boluses (ingested at -9, 15, 30 & 45 minutes respectively) of 3.2 mL.kg-1 (~960 mL total) of either a COLD (5.3°C) or a HOT drink (49.0°C), which were contrasted to a no drink CONTROL. They cycled for 60-minutes (55% PMax in hot (34.4°C) dry (34% RH) ambient conditions followed by a test to exhaustion (TTE; 80% PMax). The thermoregulatory, performance and perceptual implications of drink temperature were measured. Results. TTE was worse in the CONTROL (170 ± 132 s) than the COLD drink (371 ± 272 s; p = .021) and HOT drink conditions (367 ± 301 s; p = .038) which were not different (p = .965). Sweat responses (i.e. reflex changes in mean skin temperature (Tmsk) and galvanic skin conductance) indicated transient reductions in sweating response after COLD drink ingestion. The COLD drink improved thermal comfort beyond the transient changes in sweating. Conclusion. Only COLD drink ingestion changed thermoregulation but improved perceptual response. Accordingly, we conclude a role for gut thermoreception in thermal perception during exercise in hot, dry conditions

Enhancement of Exercise Capacity in the Heat With Repeated Menthol-Spray Application

Purpose Exercise performance is impaired in the heat and a contributing factor to this decrement is thermal discomfort. Menthol-spraying of skin is one means of alleviating thermal discomfort but has yet to be shown to be ergogenic using single spray applications. We examined whether repeated menthol-spraying could relieve thermal discomfort, reduce perception of exertion and improve exercise performance in hot (35ºC), dry (22% RH) conditions; we hypothesised it would. Method Eight trained cyclists completed two separate conditions of fixed intensity (FI) cycling (50% PMax) for 45-minutes before a test to exhaustion (TTE; 70% PMax) with 100 mL of menthol-spray (0.20% menthol) or control-spray applied to the torso after 20 and 40-minutes. Perceptual (thermal sensation (TS), thermal comfort (TC), RPE) performance (TTE duration), thermal variables (skin temperature (Tskin), rectal temperature (Trec), cardiac frequency (fc)) and sweating were measured. Data were compared using ANOVA to 0.05 alpha level. Results Menthol-spray improved TS (‘cold’ sensation cf ‘warm/hot’ after first spraying; p=.008) but only descriptively altered TC (‘comfortable’ cf ‘uncomfortable’; p=.173). Sweat production (994 (380) mL cf 1180 (380); p=.020) mL and rate (827 (327)mL·hr-1 cf 941 (319)mL·hr-1; p=.048) lowered. TTE performance improved (4.6 (1.74) cf 2.4 (1.55) minutes (p=.004). Menthol-spray effects diminished despite repeated applications indicating increased contribution of visceral thermoreceptors to thermal perception. Conclusion Repeated menthol-spray improves exercise capacity but alters thermoregulation potentially conflicting behavioural and thermoregulatory drivers; care should be taken with its use. Carrying and deploying menthol-spray would impose a logistical burden which needs consideration against performance benefit

Methodological and Validation Study of Seed Reserves in Desert Soils

The development of a method for separating seeds from desert soils, and enumerating them, is described. In the Great Basin desert, species differed greatly in their depth distribution, some having a peak at or just below the surface, while others were still abundant below 5 cm. Much higher seed densities were found beneath the canopies of shrubs and of tussock grasses than in the inter-spaces; no consistent differences were found, however, associated with the species of the canopy plant, or with distance from its center. Tentative estimates are given of the seed population in the four validation sites in Curlew Valley

"Float first and kick for your life": Psychophysiological basis for safety behaviour on accidental short-term cold water immersion

INTRODUCTION Accidental cold-water immersion (CWI) evokes the life threatening cold shock response (CSR) which increases the risk of drowning. Consequently, the safety behaviour selected is critical in determining survival; the present advice is to 'float first' and remain stationary (i.e. rest). We examined whether leg only exercise (i.e., treading water; 'CWI-Kick') immediately on CWI could reduce the symptoms of the CSR, offset the reduction in cerebral blood flow that is known to occur and reduce the CSR's symptoms of breathlessness. We also examined whether perceptual responses instinctive to accidental CWI were exacerbated by this alternative behaviour. We contrasted CWI-Kick to a 'CWI-Rest' condition and a thermoneutral control (35°C); 'TN-Rest'. METHOD Seventeen participants were tested (9 males, 8 females). All immersions were standardised; water temperature in cold conditions (i.e., 12°C) was matched ±/0.5°C within participant. Middle cerebral artery blood flow velocity (MCAv) and cardiorespiratory responses were measured along with thermal perception (sensation and comfort) and dyspnoea. Data were analysed using repeated measures ANOVA (alpha level of 0.05). RESULTS MCAv was significantly reduced in CWI-Rest (-6 (9)%; 1st minute of immersion) but was offset by leg only exercise immediately on cold water entry; CWI-Kick MCAv was never different to TN-Rest (-3 (16)% cf. 5 (4)%). All CWI cardiorespiratory and perceptual responses were different to TN-Rest but were not exacerbated by leg only exercise. DISCUSSION Treading water may aid survival by offsetting the reduction in brain blood flow velocity without changing the instinctive behavioural response (i.e. perceptions). "Float first - and kick for your life" would be a suitable amendment to the water safety advice

Acute Resveratrol Administration Increases Neural Effort but Not Whole Body Metabolism or Cognitive Performance in Healthy, Young Participants

Research into the cognitive enhancing effects of polyphenols is small but growing. Single doses of the stilbene polyphenol resveratrol can increase cerebral blood flow (CBF) but have failed to improve cognitive performance in young, healthy cohorts. As both CBF and overall energy expenditure are closely related to neural activity, this randomised, double-blind, placebo-controlled, crossover investigation, assessed the metabolic consequences of resveratrol during high cognitive demand via indirect calorimetry (ICa). Twenty-seven, self-reported healthy participants (15 male, 12 female; mean age = 22) who reported themselves free of any food intolerances and any herbal supplementation or prescription medications were recruited for the current study. Participants arrived at the testing facility at 8 a.m. on three separate occasions to complete a serial subtraction demand battery 45 min and 2 and 3 h following administration with 500 mg, 250 mg trans-resveratrol or inert placebo, while connected to an online gas analysis system. A series of within-subjects ANOVAs (with planned comparisons) revealed a significant shift towards higher carbohydrate oxidisation during cognitive demand, as indexed by a significant increase in respiratory exchange ratio (RER) at 45-min and 3-h time points, following administration of 500 mg resveratrol. Despite this, no subsequent resveratrol-related benefits to cognitive performance were observed. These results show that acute supplementation with resveratrol in young, healthy adults can modulate fuel utilization during cognitive demand, yet this does not translate into clear improvements in cognitive performance. This study adds further understanding behind the lack of cognitive effects of resveratrol in young and or healthy individuals. Future research should direct efforts towards assessing the cognitive impact of resveratrol, and other vasoactive polyphenols, in populations with age-related or dietary-induced metabolic deficits