Skeletal muscle energetics assessed by P-31-NMR in prepubertal girls with a familial predispodition to obesity

OBJECTIVE: To determine whether skeletal muscle energetics, measured by in vivo P-31-nuclear magnetic resonance spectroscopy during plantar flexion ex ercise, differ between multiethnic, prepubertal girls with or without a pre disposition to obesity. DESIGN: Cross-sectional study. SUBJECTS: Girls (mean age and body fat +/- s.d. = 8.6 +/- 0.3 y and 22.6 +/ - 4.2%) were recruited according to parental leanness or obesity defined as follows: LN (n = 22), two lean parents, LNOB (n = 18), one lean and one ob ese parent; and OB (n = 15), two obese parents. MEASUREMENTS: A 3 min, rest-exercise-recovery plantar flexion protocol was completed. Work was calculated from the force data. Spectra were analyzed f or inorganic intracellular phosphate (P-i), phosphocreatine (PCr), P-i/PCr (ratio of the low and high energy phosphates indicating the bioenergetic st ate of the cell), intracellular pH, and adenosine triphosphate (ATP). Magne tic resonance imaging was used to determine calf muscle volume. RESULTS: BMI was lower in the girls in the LN group (15.9 +/- 1.5 kg/m(2)) compared to the OB group (16.7 +/- 1.3 kg/m(2)) of girls (P < 0.05), with n o difference with the LNOB group (16.7 +/- 1.9 kg/m(2)). Adjusted for muscl e volume and cumulative work, no differences in P-i, PCr, P-i/PCr, pH, or A TP were observed among the LN, LNOB and OB groups at rest, the end of exerc ise, and after 60 and 300 s of recovery. From rest to the end of exercise, P-i and P-i/PCr (mean +/- s.d.: 0.2 +/- 0.1 vs 1.5 +/- 1.0) increased, wher eas PCr and pH (7.04 +/- 0.06 vs 6.95 +/- 0.10) decreased (all P < 0.001). By 60 s of recovery P-i and P-i/PCr decreased, whereas PCr and pH increased (all P < 0.001). CONCLUSIONS: Skeletal muscle energetics, specifically Pi/PCr and pH measure d during plantar flexion exercise, do not differ between prepubertal girls with or without a familial predisposition to obesity.