The physiological, morphological and functional responses to resistance exercise with blood flow restriction: an examination of protocol type and exercise load

Abstract

Resistance training is performed by a wide range of populations, to achieve a diverse range of outcomes in skeletal muscle. Predominantly, such outcomes include the development and/or maintenance of skeletal muscle mass and strength but may also include muscular power or endurance. Blood flow restricted (BFR) resistance exercise is recognized as a novel strategy to achieve such outcomes in skeletal muscle, with much lower-loads (20-50% of one-repetition maximum) than those traditionally employed. The capacity to reduce external loading has made BFR exercise an attractive training modality for individuals who may not tolerate high levels of mechanical stress, such as frail older persons or clinical populations. Moreover, temporarily limiting training loads and/or volume has also generated interest in BFR exercise in athletic cohorts. Despite the promise held by this modality of exercise, there is large heterogeneity in the methods (e.g., BFR methodology and exercise prescription) adopted by practitioners, which often leads to variable training outcomes. Consequently, there is a need to understand each of the many variables that comprise the BFR exercise stimulus, such as those relating to the cuff application (e.g., pressure, restriction duration etc.) and the exercise prescribed (intensity/loading, volume etc). A review of the literature (Chapter Two) identified that one particular variable receiving little attention is whether blood flow must be restricted during the inter-set recovery periods (continuous BFR), or if this is only necessary during the working periods (intermittent BFR). A greater understanding of such variables will permit the configuration of optimal and evidence-based BFR protocols, meaning that this mode of exercise may be tailored to suit the goals and health considerations of a wide spectrum of individuals. As such, this thesis encompasses a series of independent, yet related studies that examine a wide range of acute and chronic responses to different low-load BFR resistance exercise protocols, with the ultimate aim of contributing towards the current evidencebased and best-practice guidelines for BFR exercise. Study One compared chronic training adaptations between continuous and intermittent BFR protocols. The lack of differences between protocols in several morphological and functional outcomes suggested that the additional metabolic stress imposed on skeletal muscle with a continuous BFR protocol may not be necessary. However, because the study involved untrained participants, the findings may not translate to well-trained and athletic cohorts. Study Two compared differences between continuous and intermittent BFR for a wide range of acute outcomes, including neuromuscular, cardiovascular, metabolic and University Library and, subject to the policy and procedures of The University of Queensland, the thesis be made available for research and study in accordance with the Copyright Act 1968 unless a period of embargo has been approved by the Dean of the Graduate School.