Showing papers by "Geoffrey M. Minett published in 2019"

An Evaluation of Personal Cooling Systems for Reducing Thermal Strain Whilst Working in Chemical/Biological Protective Clothing.

Abstract: The use of personal cooling systems to mitigate heat strain on first-responders achieves two potential performance benefits relative to the absence of such cooling: 1) the completion of a workload with less effort; and/or 2) the completion of a greater workload for the same effort. Currently, claims made by manufacturers regarding the capability of their products for use in conjunction with chemical/biological protective clothing remain largely unsubstantiated. The purpose of this investigation was to evaluate the means by which heat strain can be alleviated during uncompensable heat stress in chemical/biological clothing, using the ASTM F2300-10 methodology. Eight healthy males completed five trials of continuous walking (4.5km·h-1; 35°C; 49% RH) for up to 120min while wearing one of four cooling systems and/or a National Fire and Protection Association 1994 Class-3 chemical/biological ensemble. The four cooling methods (ice vest [IV], phase-change vest [PCM], water-perfused suit [WS] and combination ice slurry/ice vest [SLIV]) and no cooling (CON). We observed significant improvements in trial times for IV (18 ± 10min), PCM (20 ± 10min) and SLIV (22 ± 10min), but no differences for WS (4 ± 7min). Heart rate, rectal, mean skin and body temperatures were significantly lower in all cooling conditions relative to control at various matched time points in the first 60min of exercise. Thermal sensation, comfort and perceived exertion all had significant main effects for condition, and time, there were no differences in their respective interactions. The IV, PCM and SLIV produced lower heart rate, mean skin, rectal and mean body temperatures in addition to improved work times compared to control. The WS did not improve work times possibly as a result of the cooling capacity of the suit abating, and magnifying thermal insulation. Considering the added time and resources required to implement combination cooling in the form of ice slurry and ice vest (SLIV), there was no significant additive effect for perception, cardiovascular strain, rectal temperature and total trial time relative to the phase change vest or ice vest alone. This may be a product of a ‘ceiling’ effect for work limit set to 120min as part of ASTM F2300-10.

Ballet and Contemporary Dance Injuries When Transitioning to Full-Time Training or Professional Level Dance: A Systematic Review.

Abstract: This systematic review examines the relationship between injury and two stages of a dancer's career development: when transitioning to full-time training and to a professional dance company. The findings are discussed in relation to managing transitioning loads with regard to injury prevention. Six electronic databases (PubMed, Embase, CINAHL, SPORTDiscus, Scopus, and Performing Arts Periodicals Database) were searched from inception to July 2018, inclusive of English language peer reviewed studies investigating injury in pre-professional and professional ballet and contemporary dancers. Seventeen studies met the inclusion criteria. "Limited" evidence revealed that dancers transitioning to professional ballet had a significantly higher rate of time-loss injuries per exposure hour relative to established professionals, whereas transitioning professional contemporary dancers had a significantly lower rate of both medical-attention and time-loss injuries. "Limited" evidence also showed a decreased rate and trend toward lower prevalence rates for time-loss injuries per exposure hour for transitioning ballet students and an increased rate of medical-attention injury in a combined cohort of transitioning ballet and contemporary dance students. Thus, this review provides some evidence that injuries tend to occur as dancers are transitioning to full-time ballet or contemporary dance training or to professional careers.

Passive heating and glycaemic control in non-diabetic and diabetic individuals: A systematic review and meta-analysis

Abstract: Objective: Passive heating (PH) has begun to gain research attention as an alternative therapy for cardio-metabolic diseases. Whether PH improves glycaemic control in diabetic and non-diabetic individuals is unknown. This study aims to review and conduct a meta-analysis of published literature relating to PH and glycaemic control. Methods: Electronic data sources, PubMed, Embase and Web of Science from inception to July 2018 were searched for randomised controlled trials (RCT) studying the effect of PH on glycaemic control in diabetic or non-diabetic individuals. To measure the treatment effect, standardised mean differences (SMD) with 95% confidence intervals (CI) were calculated. Results: Fourteen articles were included in the meta-analysis. Following a glucose load, glucose concentration was greater during PH in non-diabetic (SMD 0.75, 95% CI 1.02 to 0.48, P 0.050) and a glucose challenge given within 24 hours post-heating (SMD 0.30, 95% CI 0.62 to -0.02, P > 0.050). Conclusion: PH preceded by a glucose load results in acute glucose intolerance in non-diabetic and diabetic individuals. However, heating a non-diabetic individual without a glucose load appears not to affect glycaemic control. Likewise, a glucose challenge given within 24 hours of a single-bout of heating does not affect glucose tolerance in non-diabetic individuals. Despite the promise PH may hold, no short-term benefit to glucose tolerance is observed in non-diabetic individuals. More research is needed to elucidate whether this alternative therapy benefits diabetic individuals.

Acute glutamine supplementation does not improve 20-km self-paced cycling performance in the heat.

Abstract: Introduction : The premise of this study was to investigate the effect of acute glutamine supplementation on 20 km time trial cycling performance in the heat, neuromuscular function, inflammation and endotoxemia. Methods : Twelve cyclists completed two, 20-km time trials (20TT) in 35 °C (50% relative humidity). Participants ingested either glutamine (GLUT; 0.9 g∙kg-1 fat-free mass) or a placebo (CON) 60 min before each 20TT. Physiological and perceptual measures were recorded during each 20TT, and neuromuscular function assessed pre- and post-exercise. Venous blood was analysed for endotoxins, markers of gut damage (inflammatory fatty acid binding protein; I-FABP) and inflammatory cytokines (interleukin-6, IL-6; tumour necrosis factor-alpha, TNF-α). Data were analysed using linear mixed models in a Bayesian framework. Results : 20TT in the heat increased I-FABP and elevated inflammatory cytokines (IL-6 and TNF-α) compared to pre-exercise values but did not result in endotoxemia. Completion time was not statistically different between conditions (mean difference [95% credible interval] = 11 s [-23, 44]). Relative to CON, GLUT did not alter any physiological or perceptual measures during the 20TT. Conclusion : Glutamine supplementation does not improve 20TT performance in the heat or preserve neuromuscular function when compared to a placebo. These findings suggest that glutamine is not an ergogenic aid or prophylactic intervention for heat-induced gut damage during short-duration self-paced exercise in hot environments.

The effect of cycling in the heat on gastrointestinal-induced damage and neuromuscular fatigue.

Abstract: This study investigated the effect of exercise in the heat on neuromuscular function, gastrointestinal damage, endotoxemia and inflammatory cytokines. Eight male cyclists completed two 60 min cycling trials in both hot (HOT 34.5 ± 0.1 °C and 53 ± 1% relative humidity) and temperate environments (CON 20.2 ± 0.3 °C and 55 ± 3% relative humidity). The cycling task comprised of alternating 3 min intervals at a moderate-vigorous intensity (50% and 70% of maximum power output; Pmax) for 30 min, followed by 30 min at moderate intensity (40–50% Pmax). Neuromuscular function was assessed at pre-, post-exercise and 60 min post-exercise. Circulating levels of endotoxins, inflammatory cytokines and markers of gut permeability and damage were also collected at these time points. Heart rate, core temperature, skin temperature, perceived exertion, thermal sensation and comfort were also measured. Post-exercise voluntary activation of HOT (87.9% [85.2, 90.8]) was statistically lower (mean difference − 2.5% [− 4.5, − 0.5], d = 2.50) than that of CON (90.5% [87.8, 93.2]). The HOT trial resulted in statistically elevated (+ 69%) markers of gastrointestinal damage compared to CON (mean difference 0.424 ng mL−1 [0.163, 0.684, d = − 3.26]), although this was not observed for endotoxin, other inflammatory markers, or gastrointestinal permeability. This research provides evidence that short-duration cycling in the heat results in sub-optimal neuromuscular activation and increased expression of gastrointestinal damage markers, without a simultaneous elevation in circulating endotoxins or pro-inflammatory cytokines.