Submitted to: International Journal of Obesity
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 6, 2001
Publication Date: September 25, 2001
Interpretive Summary: It has been theorized that skeletal muscle energy may play a role in an individual's tendency to become obese, especially if that person has a family history of obesity. Our purpose was to find out whether skeletal muscle energy, measured by a state-of-the-art type of technology called 31P nuclear magnetic resonance spectroscopy, differs between prepubertal girls of normal weight and of varied ethnic backgrounds, depending on whether or not they have a family predisposition to obesity. We evaluated girls whose parents were both obese, girls with one obese and one lean parent, and girls whose parents were both lean. We included Caucasian, African-American and Hispanic girls in our study. Our magnetized instrument was used to measure high-energy phosphate metabolism as the girls performed a calf-muscle exercise. The results showed that skeletal muscle energetics do not differ between prepubertal girls with and without a family predisposition toward obesity. This knowledge adds important information toward the goal of prevention of obesity in children who have been shown to have a family-related propensity toward this major, health-threatening problem.
Technical Abstract: Skeletal muscle energetics may contribute to an individual's predisposition to obesity. The purpose of this study was to determine whether skeletal muscle energetics, measured by in vivo 31P-nuclear magnetic resonance spectroscopy, differ between normal-weight-for-height, multiethnic, prepubertal girls with or without a predisposition to obesity. Girls (mean age and body fat +/- SD = 8.6+/-0.3 years and 22.6+/-4.2 %) were recruited with two lean parents (LN n=22); one lean and one obese parent (LNOB n=18);or two obese parents (OB n=15). A rest-exercise-recovery protocol involving plantar flexion for 3 minutes was completed at 42+/-11% of the child's maximal voluntary contraction. Work was calculated from the force data. Spectra were analyzed for inorganic intracellular phosphate (Pi), phosphocreatine (PCr), Pi/PCr, intracellular pH, and adenosine triphosphate (ATP). Magnetic resonance imaging determined calf muscle volume. From rest to fatigue, increases in Pi (8.9+/-4.3 vs 28.4+/-8.5 % of total phosphorous) and Pi/PCr (0.2+/-0.1 vs 1.5+/-1.0) were observed, whereas PCr (44.9+/-3.8 vs 22.7+/-7.9 %) and pH (7.04+/- 0.06 vs 6.95+/-0.10) decreased (all P less than 0.001). By 60 seconds of recovery, Pi and Pi/PCr had decreased, whereas PCr and pH increased (all P less than 0.001). Adjusted for muscle volume, no differences in Pi, PCr, Pi/PCr, pH, or ATP were observed among the LN, LNOB, and OB groups at rest. Adjusted for muscle volume and cumulative work, Pi, PCR, Pi/PCr, pH, and ATP were similar among groups at fatigue, and after 60 and 300 seconds of recovery. The changes in Pi, PCR, Pi/PCr, pH, and ATP from rest to fatigue, and to recovery were similar among groups. Skeletal muscle energetics do not differ between sposition to obesity.