Skeletal muscle energetics assessed by (31)P-NMR in prepubertal girls with a familial predisposition to obesity.
OBJECTIVE
To determine whether skeletal muscle energetics, measured by in vivo (31)P-nuclear magnetic resonance spectroscopy during plantar flexion exercise, differ between multiethnic, prepubertal girls with or without a predisposition to obesity.


METHODS
Cross-sectional study.


METHODS
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 obese parent; and OB (n=15), two obese parents.


METHODS
A 3 min, rest-exercise-recovery plantar flexion protocol was completed. Work was calculated from the force data. Spectra were analyzed for inorganic intracellular phosphate (P(i)), phosphocreatine (PCr), P(i)/PCr (ratio of the low and high energy phosphates indicating the bioenergetic state of the cell), intracellular pH, and adenosine triphosphate (ATP). Magnetic 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 no difference with the LNOB group (16.7+/-1.9 kg/m(2)). Adjusted for muscle volume and cumulative work, no differences in P(i), PCr, P(i)/PCr, pH, or ATP were observed among the LN, LNOB and OB groups at rest, the end of exercise, 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, whereas 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 P(i)/PCr and pH measured during plantar flexion exercise, do not differ between prepubertal girls with or without a familial predisposition to obesity.
Treuth
M S
MS
Center for Human Nutrition, Department of International Health, Johns Hopkins University, Baltimore, Maryland 21205, USA. mtreuth@jhsph.edu
Butte
N F
NF
Herrick
R
R
D001823:Body Composition; D015992:Body Mass Index; D002153:Calorimetry, Indirect; D002648:Child; D003430:Cross-Sectional Studies; D004734:Energy Metabolism / Q000502:physiology*; D015444:Exercise / Q000502:physiology*; D005260:Female; D020022:Genetic Predisposition to Disease; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008279:Magnetic Resonance Imaging; D018482:Muscle, Skeletal / Q000378:metabolism* / Q000502:physiology; D009765:Obesity / Q000235:genetics / Q000378:metabolism*; D010101:Oxygen Consumption; D010290:Parents; D010710:Phosphates / Q000378:metabolism; D010725:Phosphocreatine / Q000378:metabolism; D010759:Phosphorus Isotopes
D010710:Phosphates; D010759:Phosphorus Isotopes; D010725:Phosphocreatine