Skeletal muscle metabolism in overweight and post-overweight women: an isometric exercise study using P-31 magnetic resonance spectroscopy

OBJECTIVE: To investigate whether skeletal muscle anaerobic metabolism, oxi dative metabolism or metabolic economy during controlled sub-maximal and ne ar-maximal exercises is altered in overweight women after diet-induced weig ht reduction, and whether these parameters are different between normal-wei ght, obesity-prone and normal-weight obesity-resistant women with similar p hysical fitness levels. DESIGN: A prospective weight loss study of overweight women and their compa rison with never overweight controls. SUBJECTS: Thirty overweight, nondiabetic, premenopausal women and 28 never overweight controls were included in this analysis. All were participating in a longitudinal investigation of the role of energy metabolism in the eti ology of obesity. The overweight women were recruited specifically to have a positive family history of obesity and have a body mass index (BMI) betwe en 27 and 30 kg/m(2) and were studied in the overweight state and after red uction to a normal weight. The never-overweight controls were recruited spe cifically to have no personal and family history of obesity and were group matched with the weight-reduced post-overweight subjects in terms of premen opausal status, age, BMI, race and sedentary lifestyle. MEASUREMENTS: All testing was performed following one month of weight maint enance and during the follicular phase of the menstrual cycle. Hydrostatic weighing was performed to measure body composition and a whole-body maximal oxygen uptake (VO2max) test was done to measure aerobic fitness. P-31 MRS was used to determine ATP production from oxidative phosphorylation (OxPhos ), 'anaerobic' glycolysis (AnGly), and creatine kinase (CK), as well as mus cle metabolic economy. The time constant of ADP (TCADP), V-PCr (ie the init ial rate of PCr resynthesis following exercise), and Q(max) (ie the apparen t maximal oxidative ATP production rate) were also calculated as additional markers of mitochondrial function. RESULTS: Diet-induced weight loss did not have any effects on the anaerobic metabolism markers (AnGly and CK). The aerobic metabolism markers calculat ed from the initial recovery data (OxPhos and V-PCr) were unaffected by die t-induced weight loss. However, diet-induced weight loss resulted in improv ements in the TCADP and Q(max) in the post-overweight state as compared to their overweight state. There were no differences in any of the anaerobic ( AnGly and CK) or oxidative metabolism markers (OxPhos, V-PCr, Q(max) and TC ADP) between the post-overweight and control groups. CONCLUSIONS: Once the overweight women were reduced to a normal-weight stat e, their skeletal muscle energy metabolism and economy was similar to the n ever overweight control women. In overweight women, oxidative metabolism or mitochondrial function may be limited by blood flow to the muscle followin g the cessation of exercise.