Search Results

You are looking at 1 - 4 of 4 items for

  • Author: Blair Crewther x
Clear All Modify Search
Restricted access

Blair Crewther, Zbigniew Obminski and Christian Cook

Purpose:

To examine the steroid hormone effect on the physical performance of young athletes during an Olympic weightlifting competition.

Methods:

26 boys and 26 girls were monitored across 2 weightlifting competitions. Pre- and post-competition testosterone (T), cortisol (C) and dehydroepiandrosterone-sulfate (DHEA-s) were measured in blood, with pre-event free T (FT) and the free androgen index (FAI) calculated. Body mass (BM) and weightlifting performance were recorded.

Results:

The boys had a larger BM, superior performance with more T, FT and a higher FAI than girls (p < .01). Although C (32%) and DHEA-s (8%) levels were elevated across competition, no sex differences in hormone reactivity were seen. In boys, DHEA-s correlated with performance (r = .46), but not after controlling for BM (r = .14). For girls, T correlated with performance (r = -0.51) after BM was controlled.

Conclusion:

The sex differences that emerge during puberty were observable, whereby the boys were larger and stronger with a more anabolic profile than girls. Individual DHEA-s (boys) and T (girls) levels were related to performance, but BM appeared to be acting as a mediating (boys) or suppressing (girls) variable. This adds new insight regarding the hormonal contribution to competitive performance in young athletes.

Restricted access

Blair Crewther, Konrad Witek, Paweł Draga, Piotr Zmijewski and Zbigniew Obmiński

D-aspartic acid (DAA) is promoted as a testosterone (T) enhancing supplement by mechanisms involving the hypothalamic–pituitary–gonadal (HPG) axis. Here, we investigated the short-term effects of DAA on serum biomarkers of the HPG-axis in male climbers. Using a single-blinded, placebo-controlled design, 16 climbers were randomly assigned to either a DAA (3 g/day) or placebo (3 g/day) supplement for 2 weeks. The reverse treatment commenced after a 2-week washout, with all conditions administered in a balanced manner. The subjects maintained their normal weekly training across this study. Serum samples taken before and after each treatment were analyzed for T, luteinizing hormone, sex hormone binding globulin, and cortisol (C), and free T was calculated (cFT). The DAA supplement did not significantly affect serum T, cFT, and luteinizing hormone levels. Only a main effect of time on sex hormone binding globulin (6.8% increase) and C (13.6% decrease) emerged (p < .03). Significant negative associations were identified between pretest values and changes (%) in T, cFT, luteinizing hormone, and C levels with DAA and/or placebo, but these relationships did not differ between treatments (p > .46). Additional measures of physical function and serum hematology also failed to respond to DAA. In summary, a daily dose of DAA during a short training period did not influence T and selected indicators of the HPG-axis in male climbers. Other parameters linked to athletic performance and health status were also unaffected. Our findings support evidence showing that DAA (including DAA-blended supplements) at either recommended or higher dosages does not afford any ergogenic benefits for athletic males.

Restricted access

Christopher M. Gaviglio, Blair T. Crewther, Liam P. Kilduff, Keith A. Stokes and Christian J. Cook

Purpose:

To assess the measures of salivary free testosterone and cortisol concentrations across selected rugby union matches according to game outcome.

Methods:

Twenty-two professional male rugby union players were studied across 6 games (3 wins and 3 losses). Hormone samples were taken 40 min before the game and 15 min after. The hormonal data were grouped and compared against competition outcomes. These competition outcomes included wins and losses and a game-ranked performance score (1–6).

Results:

Across the entire team, pregame testosterone concentrations were significantly higher during winning games than losses (P = 5.8 × 10−5). Analysis by playing position further revealed that, for the backs, pregame testosterone concentrations (P = 3.6 × 10−5) and the testosterone-to-cortisol ratio T:C (P = .038) were significantly greater before a win than a loss. Game-ranked performance score correlated to the team’s pregame testosterone concentrations (r = .81, P = .049). In backs, pregame testosterone (r = .91, P = .011) and T:C (r = .81, P = .05) also correlated to game-ranked performance. Analysis of the forwards’ hormone concentrations did not distinguish between game outcomes, nor did it correlate with game-ranked performance. Game venue (home vs away) only affected postgame concentrations of testosterone (P = .018) and cortisol (P = 2.58 × 10−4).

Conclusions:

Monitoring game-day concentrations of salivary free testosterone may help identify competitive readiness in rugby union matches. The link between pregame T:C and rugby players in the back position suggests that monitoring weekly training loads and enhancing recovery modalities between games may also assist with favorable performance and outcome in rugby union matches.

Restricted access

Blair Crewther, Christian Cook, John Fitzgerald, Michal Starczewski, Michal Gorski and Joanna Orysiak

Purpose: Reported associations between vitamin 25(OH)D and exercise performance are equivocal, perhaps due to complex interplay with cortisol and testosterone. In this study, the authors investigated serum 25(OH)D and cortisol as moderators of the testosterone relationship with exercise performance in adolescent male athletes. Methods: A total of 88 ice hockey players were assessed for serum 25(OH)D, cortisol, testosterone, body composition, and exercise performance, based on countermovement jump power and muscle torque. The authors tested independent relationships, before examining complex interactions via moderated regression analyses. Results: Most athletes (62.5%) exhibited a suboptimal (20–30 ng·mL−1) serum 25(OH)D concentration, whereas 9.1% of athletes were deficient (<20 ng·mL−1). Serum 25(OH)D was not related to performance when controlling for testing year, age, and fat mass. Further modeling revealed a significant hormonal interaction. Specifically, in low-25(OH)D subjects, testosterone predicted countermovement jump power at a high (β = 7.10, effect size = .43, P < .01), but not low (β = −3.32, effect size = −.20, P = .09), cortisol concentration. Conclusions: Serum 25(OH)D was a poor predictor of exercise performance, but it did moderate (with cortisol) the testosterone link to muscle power. Notably, this relationship emerged among individuals with a 25(OH)D concentration (∼22 ng·mL−1) approaching the deficiency cutoff. Viewing 25(OH)D as a moderating, rather than dose responsive, variable could help explain equivocal cross-sectional associations.