THE EFFECTS OF CROSS-TRAINING ON ENERGY EXPENDITURE AND UTILIZATION OF OVERWEIGHT WOMEN 476

Abstract

The purpose of this study was to determine if energy expenditure (EE) or energy utilization (EU) changed in response to cross-training. Twelve overweight women (BMI±SD=28.7±4.4) participated in a diet and exercise study while living in a metabolic research unit. The controlled diet was mildly restricted in energy (8.03±1.05 MJ·d-1). Exercise included a daily 3 mile walk, aerobic workout 5 d·wk-1, and weight training 3 d·wk-1. At the beginning (T0) and after 8 wk of training (T8), EE and EU were studied by indirect calorimetry in this sequence: at rest, following ingestion of a 1 MJ “sports bar”, during 30 min of cycling at 50% peak VO2, and for 1 hr post-exercise. Serial blood samples were obtained coincidentally and analyzed for glucose and insulin. As a result of intervention, body mass decreased by 5%, but fat-free mass decreased by only 1%. At T8, exercise EE increased 7% (p<0.01) due to modest improvements in peak VO2. The increase in EE resulted from higher carbohydrate oxidation (p≤0.01). Also during exercise at T8, plasma glucose levels were lower (T0=3.9mM vs T8=3.6mM, p≤0.01), and insulin levels did not change. These data suggest that the production of glucose during exercise did not keep pace with its utilization. Despite increased exercise EE, post-exercise EE decreased 5-7% (p≤0.01), post-prandial EE decreased 4% (p≤0.05), whereas resting EE did not change. During rest at T8, the respiratory exchange ratio tended to decrease (p=0.06), and carbohydrate oxidation decreased by 16% (p≤0.05). The small decreases in EE, post-prandial and post-exercise, could impact energy balance over time and could be viewed as a compensatory mechanism that conserves energy during a state of energy deficit. Contrary to what we expected, we found no enhancement of fat utilization as a result of cross-training.