Title

Acute effects of cluster sets on mechanical, perceptual, and hormonal responses

Date of Award

2016

Degree Type

Thesis

Degree Name

Doctor of Philosophy

School

School of Medical and Health Sciences

First Advisor

Dr G Gregory Haff

Second Advisor

Dr Sophia Nimphius

Abstract

It has been proposed that a muscle’s cross-sectional area plays a large role in a muscle’s maximal shortening velocity and its ability to produce force, making hypertrophy extremely important for all populations. Traditionally, muscle growth has been achieved by performing large volumes of work with short rest periods in between sets, resulting in large amounts of acute neuromuscular fatigue, possibly resulting in short-term decreases in strength or power output. More recently, research has shown that hypertrophy can also be stimulated by training with loads that are well below or above the previously mentioned load recommendations. Regardless of the training method used, an underlying theme within many hypertrophy-based studies is that increasing the amount of mechanical work increases the amount of time under tension and metabolic stress, yielding a hypertrophic response. By utilizing cluster sets, which involve resting between groups of repetitions within a set, partial recovery of adenosine triphosphate and phosphocreatine stores may allow for greater training loads for a given volume, or a greater volume for a given load. By increasing the load, training volume, or both, a greater amount of external work may be accomplished, effectively increasing metabolic stress, the time that the muscle is under tension, and ultimately muscle growth. Studies that examine cluster sets in this manner are scarce and many use protocols that are not necessarily designed for developing skeletal muscle hypertrophy. Therefore, the purpose of the studies included in this dissertation was to investigate the acute effects of cluster sets using high volume back squats. By doing so, it would be possible to determine how acute program variables can be manipulated to create alternative resistance-training methods that may result in greater hypertrophy than traditional sets without increasing acute neuromuscular fatigue. The acute effects of set-structure (Study 1), training load (Study 2), and rest interval duration and frequency (Study 3) were determined in order to determine how these acute exercise variables can be manipulated in order to simultaneously target a combination of training goals such as increasing strength, power development, and skeletal muscle hypertrophy.

Specifically, Study 1 showed that cluster sets allowed for movement velocity and power output to be maintained compared to traditional sets, during which velocity and power output significantly decreased. Study 2 showed that more frequent intra-set rest intervals allowed for a greater external load to be lifted for a given number of repetitions, resulting in greater total work and time under tension without decreasing relative movement velocity. Lastly, Study 3 showed that when using the same total rest duration, external load, and number of repetitions, changing the frequency and duration of intra-set rest intervals did not affect mechanical, metabolic, or hormonal responses. Therefore, this series of studies concludes that cluster sets can be manipulated in a variety of ways that may induce different training adaptations.

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