James M. Green

The Influence of Hydration on Anaerobic Performance: A Review.

This review examines the influence of dehydration on muscular strength and endurance and on single and repeated anaerobic sprint bouts. Describing hydration effects on anaerobic performance is difficult because various exercise modes are dominated by anaerobic energy pathways, but still contain inherent physiological differences. The critical level of water deficit (∼ 3–4%; mode dependent) affecting anaerobic performance is larger than the deficit (∼ 2%) impairing endurance performance. A critical performance-duration component (> 30 s) may also exist. Moderate dehydration (> 3% body weight; precise threshold depends on work/recovery ratio) impairs repeated anaerobic bouts, which place an increased demand on aerobic metabolism. Interactions between dehydration level, dehydration mode, testing mode, performance duration, and work/recovery ratio during repeated bouts make the dehydration thresh-old influencing anaerobic performance mode dependent.

Caffeine and diuresis during rest and exercise: A meta-analysis

OBJECTIVES Although ergogenic, acute caffeine ingestion may increase urine volume, prompting concerns about fluid balance during exercise and sport events. This meta-analysis evaluated caffeine induced diuresis in adults during rest and exercise. DESIGN Meta-analysis. METHODS A search of three databases was completed on November 1, 2013. Only studies that involved healthy adults and provided sufficient information concerning the effect size (ES) of caffeine ingestion on urine volume were included. Sixteen studies met the inclusion criteria, providing a total of 28 ESs for the meta-analysis. Heterogeneity was assessed using a random-effects model. RESULTS The median caffeine dosage was 300 mg. The overall ES of 0.29 (95% confidence interval (CI) = 0.11-0.48, p = 0.001) corresponds to an increase in urine volume of 109 ± 195 mL or 16.0 ± 19.2% for caffeine ingestion vs. non-caffeine conditions. Subgroup meta-analysis confirmed exercise as a strong moderator: active ES = 0.10, 95% CI = -0.07 to 0.27, p = 0.248 vs. resting ES = 0.54, 95% CI = 0.22-0.85, p = 0.001 (Cochrans Q, p = 0.019). Females (ES = 0.75, 95% CI = 0.38-1.13, p < 0.001) were more susceptible to diuretic effects than males (ES = 0.13, 95% CI = -0.05 to 0.31, p = 0.158) (Cochrans Q, p = 0.003). CONCLUSIONS Caffeine exerted a minor diuretic effect which was negated by exercise. Concerns regarding unwanted fluid loss associated with caffeine consumption are unwarranted particularly when ingestion precedes exercise.

Evaluation of a carbon dioxide personal cooling device for workers in hot environments.

This study tested the effectiveness of a carbon dioxide cooling device in reducing heat strain for workers in a hot and humid environment. Ten participants completed two trials in an environment of 30°C WBGT (75% relative humidity) with a novel liquid carbon dioxide cooling shirt (CC) or no cooling (NC) in a randomized order. Mean time-weighted workload for each individual equaled 465 W (400 Kcals· h−1). In the CC condition, the work time was significantly increased by 32% (97 ± 36 min) compared with NC (74 ± 26 min) (p < 0.05). There was no significant difference in mean skin temperature over the trials. Rectal temperature (T re ) was significantly different after 50 min (p < 0.05). Mean heart rate, the delta T re increase rate, and heat storage at 55 min (last point with n = 8) were significantly lower in CC (p < 0.05). Overall heat storage was 54 ± 41 W and 72 ± 40 W for CC and NC, respectively (p < 0.05). Participants also indicated favorable subjective responses for CC vs. NC (p < 0.05). These findings suggest that this novel cooling device would effectively attenuate heat strain and increase work productivity for personnel working in a hot and humid environment. Practical aspects of use such as cost, convenience, weight, cooling duration, and rise in ambient CO2 concentration in confined spaces must also be considered.

Attitude and Knowledge Changes in Collegiate Dancers following a Short-Term, Team-Centered Prevention Program on Eating Disorders

Eating knowledge, nutritional knowledge, and psychological changes among female collegiate dancers were examined before and after a 4-wk. team-centered program on sport nutrition, exercise, and disordered eating consequences. Collegiate female dancers from two NCAA Division I institutions participated in a control (n = 19; M age = 19.1 yr., SD = 1.0) or intervention (n = 21; M age = 19.2 yr., SD = 1.2) group. Measures were administered to both groups before and after intervention to assess eating disorders, depression, and nutritional and disordered eating knowledge. There was a statistically significant increase in scores on nutritional and overall eating disorder knowledge in the intervention group compared to the control group. Mean scores on depression, drive for thinness, body dissatisfaction, and maturity fears decreased in the intervention group.

Influence of carbohydrate mouth rinsing on running and jumping performance during early morning soccer scrimmaging

Abstract Carbohydrate mouth rinse (CMR) is a novel method proposed to enhance endurance performance lasting ≤ 60 min. The current study examined the influence of CMR on anaerobic performance tasks in 11 collegiate female soccer players after an overnight fast. Athletes completed two experimental sessions, during which carbohydrate (CHO; 6% maltodextrin) or taste- and colour-matched placebo (PLA) mouth-rinse solutions were administered in a counterbalanced, double-blinded design. Three rounds of a 5-min scrimmage bout and series of performance tests including a single countermovement vertical jump (1VJ), a set of four consecutive vertical jumps, a 72-m shuttle run (SR72) and 18-m sprint comprised each trial. Thirst sensation (TS), session TS, ratings of perceived exertion (RPE) and session RPE were assessed as secondary outcomes. The first SR72 approached significance (p = 0.069), but no significant between-trials differences were observed for any of the mean performance tasks. The highest 1VJ scores did not differ for the first (CHO = 47.3 ± 3.4, PLA = 47.7 ± 3.5 cm; p = 0.43), second (CHO = 48.0 ± 4.1, PLA = 47.9 ± 3.5 cm; p = 0.82) or third bout (CHO = 47.4 ± 3.9, PLA = 48.1 ± 3.9 cm; p = 0.26). TS approached significance (p = 0.053) during the first bout. No significant differences (p > 0.05) were found for any of the perceptual variables. Current results fail to support ergogenic influence of CMR on anaerobic performance tasks in collegiate female athletes.

Hydration kinetics and 10-km outdoor running performance following 75% versus 150% between bout fluid replacement

Abstract Current American College of Sports Medicine (ACSM) guidelines recommend replacing 150% of sweat losses between training bouts separated by ≤12 hours, but little evidence exists concerning the implications of this strategy for runners. Participants (n = 13) in this study replaced 75% (1637 ± 372 mL) or 150% (3099 ± 850 mL) of sweat losses following an outdoor evening run (∼75 minutes; Wet-bulb-globe temperature (WBGT) = ∼27°C) and consumed a standardised evening meal and breakfast before completing an outdoor (WBGT = ∼23°C) 10-km time-trial the following morning. Urine was collected between runs and urine specific gravity (USG) was assessed pre-run. Significant differences were found in pre-run body mass (75% = 69.6 ± 9.2; 150% = 70.1 ± 9.3 kg; P = 0.02) and USG (75% = 1.026 ± 0.005; 150% = 1.014 ± 0.007; P < 0.001). Heart rate during 10-km run (168 ± 14 versus 168 ± 12 beats min−1) and post-run intestinal temperature (39.08 ± 0.52 versus 39.00 ± 0.70 °C) did not differ for 75% and 150%, respectively, despite an ∼3% performance improvement (75% = 47.28 ± 6.64; 150% = 45.93 ± 6.04 minutes; P = 0.001) due to a faster pace in the second half of the run with 150% replacement. Session rate of perceived exertion (RPE) was lower (P = 0.02) during 150% (7.5 ± 1.3) versus 75% (8.4 ± 0.9). Reluctant drinkers potentially hinder training quality between evening and morning runs in the heat, but copious urine production and difficulty in consuming recommended fluid volumes suggest fluid replacement <150% may be more ideal.

Physiological and comfort effects of a commercial "cooling cap" worn under protective helmets.

Ballistic protective helmets can impair heat dissipation. A cooling device in the helmet (cooling pad, CP) could help prevent heat problems in military personnel and potentially enhance comfort. This study examined the effects of CP on rectal and skin temperatures, heart rate, percent change in plasma volume, urine specific gravity, rating of perceived exertion, and other subjective measures while performing light work in a hot environment. It was hypothesized that the CP would act as an insulator to the head, which would not positively affect any physiological variable but could positively affect wearer subjective comfort or temperature. Participants performed a work protocol for ∼ 2 hr. A ballistic vest, slacks, short-sleeved button-up shirt, and a ballistic helmet (one trial with CP and one trial without) were worn. Repeated measures analysis of variance (ANOVA) showed no differences (p > 0.05) between wearing and not wearing the CP for any physiological parameter. However, participants perceived the CP as cooler (p = 0.002). Other trends in perceptual data such as thermal strain and helmet comfort indicated the CP felt cooler. However, based on forehead temperature and participant comments, the CP lost its cooling ability relatively quickly (within ∼ 30 min).