Document Type

Thesis

Publication details

Crewther, BT 2009, 'New evidence for the short-term effects of testosterone and cortisol upon athletic performance and training adaptation in elite male rugby players', PhD thesis, Southern Cross University, Lismore, NSW.

Copyright BT Crewther 2009

Abstract

For elite athletes, testosterone and cortisol play an important role in the training process by controlling long-term muscle growth and performance. Studies now support the existence of short-term hormonal effects upon athletic performance and training adaptation, especially for strength-trained athletes. Elite rugby players represent one group of strength athletes for which there is little hormonal information. The major aims of the work in this thesis were to measure, confirm and utilize the short-term effects of testosterone and cortisol to improve performance and adaptation in elite male rugby players.

Experiment one validated the salivary testosterone (Sal-T) and cortisol (Sal-C) concentration (v. plasma) measures during dynamic changes induced by a 30-second cycle sprint, and confirmed the ability of sprint exercise to elevate the salivary hormones. Experiment two was undertaken to confirm hormonal relationships with running speed, squat jump (SJ) and bench throw (BT) power, and box squat (BS) and bench press (BP) one repetition maximum (1RM) strength in rugby players. The salivary hormone concentrations of players correlated to various speed, power and strength measures. This study also revealed performance similarities and differences between larger rugby forwards and smaller backs. Allometric scaling was found effective in normalizing power and strength in rugby forwards and backs in Experiment three.

Experiments four and five evaluated the effects of sprint exercise (as a potentiating stimulus) upon the salivary hormones and workout performance and training adaptation in rugby players. A 40-second cycle sprint improved BS 1RM (2.6 ± 1.2%) and elevated Sal-T concentrations. A 40-second grinder sprint also improved BP 1RM (2.8 ± 1.0%) with the workout differences (%) in hormone concentrations correlating to BP performance. Thus, the salivary hormonal changes that occurred offered one possible mechanism to explain these improvements. These results were not replicated in a four-week training study. The training group performing a 40-second cycle sprint showed similar improvements in SJ power (peak 8.2 ± 2.9%, mean 11.8 ± 2.6%) and BS 1RM (20.5 ± 2.6%), compared to a control group (11.9 ± 3.6%, 18.6 ± 4.8%, 23.2 ± 1.3%, respectively). Still, for all players combined, resting salivary hormone concentrations were correlated to workout power and strength, thereby potentially moderating the training improvements. This work provides new evidence for the short-term effects of testosterone and cortisol upon athletic performance and training adaptation in elite male rugby players. This is novel information with important implications for examining, interpreting and utilizing hormones in sport science research and practice.

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