Despite clear recommendations on the minimal amount of physical activity for achieving health benefits and reducing risk of chronic disease, the majority of people in the Western world remain sedentary. As a 'lack of time' has been identified as one of the main barriers to becoming and remaining physically active, in the past decade research has focused on high-intensity interval training (HIT) as a time-efficient alternative to aerobic exercise. Although initial studies convincingly demonstrated equal or better health benefits with various HIT protocols compared to much larger volumes of aerobic exercise, these HIT protocols tend to be very strenuous and as such are unlikely to be adhered to by sedentary populations. Furthermore, most HIT protocols are not as time-efficient as sometimes claimed, with the total time per exercise session generally exceeding 20-30 minutes. This thesis aimed to characterise the effects of a novel reduced-exertion HIT (ReHIT) protocol, requiring a maximum of 2 x 20 s all-out sprint efforts in a 10 min training session, upon insulin sensitivity, aerobic capacity, glycogen utilisation and associated acute metabolic responses. The ReHIT exercise bouts were well tolerated by participants, but were associated with a substantial disturbance of physiological homeostasis including muscle glycogen degradation, lactate accumulation, excursions in plasma volume, post-exercise oxygen consumption, respiratory exchange ratio and heart rate, as well as a skeletal muscle signalling response through AMPK, and increases in skeletal muscle GLUT4 and PGC1α mRNA expression (Chapter 4 and 5). The combined training studies (n=49) provide some support for improvements in key disease biomarkers following ReHIT, with improvements in insulin sensitivity observed in men, and increased aerobic capacity observed in men and women (Chapter 7). These observations highlight a potential regulatory role for glycogen in exercise-induced adaptation. However, the mean improvements in insulin sensitivity in men were not consistent between the two training studies (Chapter 2 and 6), and there was a high level of variability observed between individuals (Chapter 6 and 7). Therefore, the impact of ReHIT on insulin sensitivity needs to be further explored in the context of a randomised controlled trial, and the mechanisms underpinning the large variability in adaptive response need to be characterised.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:667740 |
| Date | January 2015 |
| Creators | Metcalfe, Richard Sean |
| Contributors | Vollaard, Niels ; Thompson, Dylan |
| Publisher | University of Bath |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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