Age is independently related to muscle metabolic capacity in premenopausal women

Departments of 1 Human Studies, 2 Nutrition Sciences, 3 Diagnostic and Therapeutic Sciences, and 7 Physiology and Biophysics, University of Alabama at Birmingham, Birmingham, Alabama 35294; 4 Physical Therapy Program, The University of Findlay, Findlay, Ohio 45840; 5 Pennington Biomedical Research Center, Louisiana State University, Baton Rouge, Louisiana 70803; and 6 Division of Kinesiology, Laval University and Laval Hospital Research Center, Sainte-Foy, Quebec City, Quebec, Canada G1K 7P4 The purpose of this study was to determine whether muscle metabolic capacity was inversely related to age after adjusting for physical activity in sedentary premenopausal women. Eighty-three women (ages 23-47 yr) had their free-living, activity-related energy expenditure evaluated with doubly labeled water procedures, and room calorimeter determined sleeping energy expenditure. Maximum O 2 uptake and strength were evaluated in all subjects, whereas 31 P-magnetic resonance spectroscopy determined metabolic economy during maximal exercise, and muscle biopsy maximal enzyme activity was evaluated in subsets of the sample (48 and 18 subjects, respectively). Age was significantly related to whole body treadmill endurance time ( r = 0.32), plantar flexion strength ( r = 0.29), maximum O 2 uptake ( r = 0.27), 31 P-magnetic resonance spectroscopy ADP recovery rate ( r = 0.44), and anaerobic glycolytic capacity ( r = 0.37), and muscle biopsy citrate synthase activity ( r = 0.48), glyceraldehyde-3-phosphate dehydrogenase ( r = 0.54), phosphofructokinase ( r = 0.62), and phosphorylase ( r = 0.58) activity even after adjusting for activity-related energy expenditure. These data suggest that, in sedentary premenopausal women, both oxidative and glycolytic muscle capacity decrease with age even when physical activity is taken into account. energy expenditure; aerobic capacity; anaerobic capacity