title: High intensity exercise: health and performance perspectives
Creators: name: Whyte, Laura J.
Publisher: name: University of Glasgow
Year: 2012
Subjects: subject: High intensity exercise, sprint interval training, insulin sensitivity, overweight, sedentary, elite, cyclists, preconditioning

description: For many years, high intensity exercise has been associated with sports training and performance. However, more recently, high intensity exercise has been adopted as a form of physical activity to induce health gains. This thesis considers two areas of exercise physiology that are bound by the theme of very high intensity exercise, but which are distinct in both focus and application. As such, the thesis is split into two sections: Section I investigates the use of very high intensity exercise in relation to improving health-related outcomes in an overweight/obese sedentary population; Section II aims to use a novel approach to improve very high intensity exercise performance in well-trained, elite and world-class athletes. 

Section I
Physical activity is important in maintaining and promoting good health. Yet, physical activity levels remain low in most parts of the developed world. Much previous work has focussed on using submaximal intensity exercise in improving health with few studies exploring the use of shorter duration, supramaximal exercise. More specifically, it was unknown whether a specific type of supramaximal intensity exercise known as sprint interval training (SIT) could improve health-related variables in an “at risk” population. Ten overweight/obese sedentary men undertook two weeks of SIT (6 sessions of repeated 30 s “all-out” cycle sprints). The intervention increased insulin sensitivity and fat oxidation by 23.3 ± 7.6% and 18.2 ± 8.9% respectively, whilst there was a concomitant reduction in carbohydrate oxidation (by 62.5 ± 18.4%) and lower mean arterial blood pressure (by 4.7 ± 2.4%) 24 h after the final session. However, by 72 h these improvements failed to be significant (all p&gt;0.05). Therefore, although two weeks of supramaximal training improved many health-related variables, it was unknown whether this was the consequence of the last bout (i.e. an acute effect), or whether it was a short-lived training response. To evaluate this question, ten overweight/obese sedentary men performed a single session of SIT (i.e. 4 x 30 s “all-out” cycle sprints with 4.5 minute recovery between sprints). In addition, due to lack of time being cited as a key variable for not exercising, a shorter duration training episode was employed which was matched with the SIT for total work done, but which excluded the recovery period (i.e. a single extended sprint). Substrate utilisation was altered; having a greater reliance on fat oxidation after both exercise trials (by 62.5 ± 8.8% and 37.5 ± 7.8% for SIT and the single extended sprint respectively). However, insulin sensitivity and post-exercise blood pressure were improved only in the extended sprint (by 44.6 ± 22.2% and 5.7 ± 1.7% respectively). Thus, this section of the thesis illustrated that supramaximal intensity exercise enhanced health-related outcomes and has provided an initial insight into the minimum duration of exercise that is required to induce health benefits. 

Section II
At the highest level of sporting performance, the smallest of margins can determine the outcome. Therefore, interest in novel strategies to improve performance is sought. Preconditioning is traditionally a method used in clinical situations whereby one or more cycles of a stressor is applied to a tissue/organ in order for it to protect against subsequent bouts of that stressor. Using the novel approach of ischaemic and hypoxic preconditioning, nine male well-trained athletes completed two 5 minute cycles of ischameia/hypoxia before an “all-out” 60 s sprint. Although not statistically significant (p&gt;0.05), large magnitudinal differences in mean and peak power were found between ischaemic/hypoxic preconditioning and control (2.5 ± 2.8% and 2.5 ± 1.6% for mean power and 3.1 ± 3.0% and 3.3 ± 0.5% for peak power in ischaemic and hypoxic preconditioning trials respectively). There were also large inter-individual responses, which suggested that there were responders and non-responders; in particular, effects appeared to be greater in those who had backgrounds in power-based sports. Therefore to evaluate whether the benefits were greater in sprint/power-based athletes, four elite and world-class sprint track cyclists completed hypoxic preconditioning before repeated 500 m “all-out” sprints. Hypoxic preconditioning did not improve 500 m performance. However, these pilot studies offer an introduction to the use of preconditioning within the sporting performance field and with further study may be a useful technique.