Date of Award

Fall 2012

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Kinesiology

Supervisor

Stuart Phillips

Language

English

Abstract

There is a prevalent belief that acute hormone responses to resistance exercise mediate adaptations in skeletal muscle hypertrophy; however, there is little supporting evidence. We conducted studies to examine the relationship between acute hormonal increases after resistance exercises and subsequent changes in muscle anabolism.

We tested the hypothesis that exercise-induced responses of anabolic hormones—growth hormone (GH) and testosterone—would enhance rates of myofibrillar protein synthesis (MPS) after an acute bout of resistance exercise, and would augment muscle hypertrophy after training. We concluded, however, that resistance exercise-induced increases in putative anabolic hormones do not enhance MPS or hypertrophy.

We also examined whether rates of MPS would be attenuated in women (compared with men) after resistance exercise, due to their lack of post-exercise testosteronemia. We reported similar increases in MPS in men and women; post-exercise testosterone responses in women, which were 45-fold lower than men, did not attenuate elevations in MPS.

Collectively, our work leads to the conclusion that the acute rise in hormones such as testosterone and GH has very little bearing on MPS and hypertrophy responses to resistance exercise. Instead, the rise in these hormones appears to be a non-specific response to exercise stress rather than a response that is important for muscle anabolism. Contrary to widely used principles, our data suggests that exercise programs should not be designed based on nuances in the post-exercise hormonal milieu. Alternatively, understanding local mechanotransduction, which is directly linked to muscle fibre loading, will reveal the processes that drive human exercise-mediated muscle hypertrophy.

McMaster University Library


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