Muscle energetics changes throughout maturation: a quantitative 31P-MRS analysis.
We quantified energy production in 7 prepubescent boys (11.7 ± 0.6 yr) and 10 men (35.6 ± 7.8 yr) using (31)P-magnetic resonance spectroscopy to investigate whether development affects muscle energetics, given that resistance to fatigue has been reported to be larger before puberty. Each subject performed a finger flexions exercise at 0.7 Hz against a weight adjusted to 15% of their maximal voluntary strength for 3 min, followed by a 15-min recovery period. The total energy cost was similar in both groups throughout the exercise bout, whereas the interplay of the different metabolic pathways was different. At the onset of exercise, children exhibited a higher oxidative contribution (50 ± 15% in boys and 25 ± 8% in men, P < 0.05) to ATP production, whereas the phosphocreatine breakdown contribution was reduced (40 ± 10% in boys and 53 ± 12% in men, P < 0.05), likely as a compensatory mechanism. The anaerobic glycolysis activity was unaffected by maturation. The recovery phase also disclosed differences regarding the rates of proton efflux (6.2 ± 2.5 vs. 3.8 ± 1.9 mM · pH unit(-1) · min(-1), in boys and men, respectively, P < 0.05), and phosphocreatine recovery, which was significantly faster in boys than in men (rate constant of phosphocreatine recovery: 1.3 ± 0.5 vs. 0.7 ± 0.4 min(-1); V(max): 37.5 ± 14.5 vs. 21.1 ± 12.2 mM/min, in boys and men, respectively, P < 0.05). Our results obtained in vivo clearly showed that maturation affects muscle energetics. Children relied more on oxidative metabolism and less on creatine kinase reaction to meet energy demand during exercise. This phenomenon can be explained by a greater oxidative capacity, probably linked to a higher relative content in slow-twitch fibers before puberty.
Tonson
Anne
A
Centre de Résonance Magnétique Biologique et Médicale, UMR Centre National de la Recherche Scientifique 6612, Faculté de Médecine de Marseille, Université de la Méditerranée, Marseille, France.
Ratel
Sébastien
S
Le Fur
Yann
Y
Vilmen
Christophe
C
Cozzone
Patrick J
PJ
Bendahan
David
D
D000255:Adenosine Triphosphate / Q000378:metabolism; D000293:Adolescent; D000328:Adult; D002648:Child; D003402:Creatine Kinase / Q000378:metabolism; D004734:Energy Metabolism; D006019:Glycolysis; D018737:Hand Strength; D006801:Humans; D007537:Isometric Contraction; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D008297:Male; D008875:Middle Aged; D024510:Muscle Development; D018482:Muscle, Skeletal / Q000254:growth & development / Q000378:metabolism*; D010084:Oxidation-Reduction; D010725:Phosphocreatine / Q000378:metabolism; D010759:Phosphorus Isotopes; D020127:Recovery of Function; D046468:Sexual Development; D055815:Young Adult
D010759:Phosphorus Isotopes; D010725:Phosphocreatine; D000255:Adenosine Triphosphate; D003402:Creatine Kinase