Submitted to: American College of Sports Medicine
Publication Type: Abstract Only
Publication Acceptance Date: 5/30/1996
Publication Date: N/A
Technical 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 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). Exercise included a daily 3 mile walk, aerobic workout 5 d/wk, and weight training 3 d/wk. At the beginning (T0) and after 8 wk of training (T8), EE and EU were studied by indirect calorimetry 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 V02. The increase in EE resulted from higher carbohydrate oxidation (p-0.01). Also during exercise at T8, plasma glucose levels were lower (p-0.01), and insulin levels did not change. Apparently 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.