Effect of acute caloric restriction on work efficiency.

Whether caloric restriction can alter the efficiency of muscular work raises important questions regarding the control of energetic coupling processes and the efficacy of exercise as a treatment for obesity. To address these issues, oxygen uptake (VO2) was determined at rest and during incremental cycle ergometry in 13 moderately obese (133 +/- 3% ideal body weight, means +/- SEM) women during weight maintenance and after 3 wk of caloric restriction (800 kcal/d). Work efficiency was calculated from the linear portion of the VO2-work rate relationship. Caloric restriction decreased body weight 4.0 +/- 0.4 kg (p less than 0.05), VO2 at rest 32 +/- 3 mL/min (p less than 0.05), and VO2 during unloaded (0 W) cycling 47 +/- 14 mL/min (p less than 0.05). However, work efficiency was unchanged (ie, -0.3 +/- 1.2%, NS). We conclude that, despite metabolic adaptations resulting in decreased energy expenditure at rest and during zero Watt cycling, acute caloric restriction does not alter work efficiency.