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EXERCISE INTENSITY, EXERCISE TRAINING AND ENERGY METABOLISM IN OVERWEIGHT AND OBESE MALES
A thesis submitted in fulfilment of the requirements for the award of: Doctor of Philosophy
Submitted By: Darren Mark Roffey BAppSc, BHSc (hons.)
Institute of Health and Biomedical Innovation School of Human Movement Studies Faculty of Health Queensland University of Technology 2008
KEYWORDS
obesity, substrate utilisation, fat oxidation, resting metabolic rate, maximum aerobic power, physical activity, FATmax, energy expenditure, non-exercise activity thermogenesis, body composition, accelerometry, heart rate monitoring, exercise prescription, dietary intake
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ABSTRACT
Obesity prevalence rates are continually increasing in many developed and developing countries. Considerable research has been undertaken to identify efficacious methods to help alleviate the array of health disorders commonly associated with obesity. Participation in regular aerobic exercise is now considered an essential component in any long-term obesity management strategy because of its potential to provide metabolic benefits and assist in the maintenance of energy balance.
Although engagement in moderate-intensity exercise
training may be preferable to high-intensity exercise training due to the perceived lower risk of musculoskeletal injury and better adherence, there is some ambiguity regarding the optimal exercise intensity for weight loss and the reduction of related co-morbidities. Obese individuals have large fat stores, which in some instances, can paradoxically co-exist with an impaired ability to utilise fat as a fuel source. Exercise training at a moderate-intensity which maximises fat oxidation may therefore be more beneficial in targeting central and peripheral adiposity and improving a number of associated health parameters such as fasting blood lipid profile and resting blood pressure compared to work-matched high-intensity training with a greater glycolytic dependence. However, sufficient evidence suggests that although high-intensity exercise is associated with low fat oxidation during the exercise session per se, in the hours post-exercise there is an increase in the level of lipolysis. To date, the evidence for the differential effect of moderate- versus high-intensity exercise on 24-hour energy expenditure is equivocal. Understanding the impact of exercise intensity on total daily energy expenditure is thereby important as this determines whether the training has resulted in a negative energy balance required for weight loss. In determining whether training at a moderate- or high-intensity is more beneficial for eliciting metabolic health improvements for obese individuals, consideration of the acute response to the exercise session is important. Conversely, of equal relevance is how different exercise intensities impact the energy metabolism of an individual, and what effect these training intensities conducted over a number of months will have on metabolic, physiological and psychosocial markers of health. Total daily energy expenditure (TEE) is a composite of resting metabolic rate (RMR), thermic effect of food (TEF) and activity energy expenditure (AEE).
While RMR is
proportionally the largest component, AEE is the most variable, with the greatest capacity to be modulated.
To accurately investigate the impact of training at different exercise
intensities on the metabolic, physiological and psychosocial health profiles of an obese cohort, it is necessary to firstly establish whether it is possible to quantify a training effect on
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RMR in comparison to the variance observed under normal sedentary conditions. Secondly, given that the majority of exercise training is prescribed as a percentage of maximum aerobic
& O2max), it is vital to understand the effects of different testing protocols on the power ( V final end-point. This is important in order to select the test most likely to produce accurate
& O2max and mechanical work values for exercise prescription purposes. Thirdly, it is only V recently that the concept of training at the intensity which elicits maximal fat utilisation (FATmax) has been identified as a potentially important factor for consideration in exercise interventions. There are numerous elements involved with the calculation and utility of FATmax which need to be investigated to ensure its accuracy and precision before implementation.
In this program of research, the completion of three extensive
methodological studies was required before investigating the primary research question relating to the effect of training at different exercise intensities on the metabolic, physiological and psychological health profiles of overweight and obese males. To ascertain if the magnitude of change in RMR observed during an exercise training intervention is meaningful, it is imperative to first identify the day-to-day within-individual variability under normal sedentary conditions using the various technologies available. Therefore, the aim of the first study was to systematically compare the variation in RMR measured using ventilated hood and mouthpiece and nose-clip indirect calorimetry systems. RMR was measured in 10 healthy adults during five separate testing sessions within a twoweek period where ad-libitum diet intake was continued and normal activities of daily physical activity were maintained. Each testing session consisted of one measurement of RMR using a ventilated hood system, followed by another using a mouthpiece and nose-clip system. No significant difference in RMR was evident between measurement sessions using either indirect calorimeter. However, oxygen consumption and RMR were higher using the mouthpiece and nose-clip system (P
