Lean body mass is an important determinant of resting and 24-hour energy expenditure. Individuals who suffer spinal cord injuries experience a marked loss of muscle mass which may decrease energy expenditure and promote an increase in body fat. This project tests the hypothesis that energy expenditure is decreased in patients with spinal cord injuries as a consequence of their marked muscle atrophy. Resting metabolic rate (measured by indirect calorimetry) and body composition (dual-energy X-ray absorptiometry (DXA)) will be compared in subjects with spinal cord injuries and age-matched able-bodied individuals. In addition, 24-hour energy expenditure is measured in a respiratory chamber in paraplegic individuals who are fully independent in self care. To date, 17 individuals (12 males, 5 females) with spinal cord injuries have been studied. Of these, 9 were paraplegic and 8 quadraplegic (7 males and 1 female). Mean percent body fat was 10-12% higher than predicted, whereas lean body mass was 10-15% less than predicted. Percent body fat was significantly correlated with lesion level (p<0.05) and could be predicted using a linear combination of thigh, hip, and triceps skinfolds which together explained 90% of the variance in percent body fat. Resting metabolic rate also was 12-15% less than expected. These results confirm earlier observations that individuals who have suffered spinal cord injuries have less lean body mass and a greater proportion of fat than able-bodied controls. In addtion, energy expenditure is lower in proportion to the loss of lean body mass. A better understanding of the relationship between changes in body composition and energy expenditure in patients with spinal cord injuries may eventually suggest strategies to reduce the excess risk of diabetes and cardiovascular disease in this population. These studies also may improve our understanding of the contributions of muscle mass to energy expenditure in the general population as well as in other special populations characterized by a loss of muscle mass (such as the elderly).
