Quantifying the effect of exercise on total energy expenditure in obese women

The prevalence of obesity continues to increase despite considerable research and innovation regarding treatment and management strategies. When completed as prescribed, exercise training is associated with numerous health benefits and predictable levels of weight loss. However, under free-living conditions the benefits of exercise are less consistent, suggesting that non-adherence and/or a compensatory response in non-exercise activity thermogenesis (NEAT) may be occurring. The accurate quantification of all components of total energy expenditure (TEE), including TEE itself, was imperative to elucidate the primary research question relating to the impact of exercise on TEE. In addition, the measurement of changes in body composition and the response to prescribed exercise were assessed in methodological and pilot investigations. Following this extensive background, the primary research question relating to the effect of exercise on levels of TEE and the associated implications of such a compensatory response could be more rigorously investigated. The first study investigated the variability in isotopic equilibrium time under field conditions, and the impact of this variability on estimates of total body water (TBW) and body composition when using the deuterium dilution technique. Following the collection of a fasting baseline urine sample, 10 women and 10 men were dosed with deuterium oxide (0.05g/kg body weight). Urine samples were collected every hour for 8 hours. The samples were analysed using isotope ratio mass spectrometry and time to equilibration was determined using three commonly employed data analysis approaches. Isotopic equilibrium was reached by 50, 80 and 100% of participants at 4, 6 and 8 h, respectively. The mean group equilibration times determined using the three different plateau determination methods were 4.8 ± 1.5, 3.8 ± 0.8, and 4.9 ±1.4 h, respectively. Isotopic enrichment, TBW, and percent body fat estimates differed between early sampling