Oxidative capacity and ageing in human muscle

1. This study determined the decline in oxidative capacity per volume of hu man vastus lateralis muscle between nine adult (mean age 38.8 years) and 40 elderly (mean age 68.8 years) human subjects (age range 25-80 years). We b ased our oxidative capacity estimates on the kinetics of changes in creatin e phosphate content ([PCr]) during recovery from exercise as measured by P- 31 magnetic resonance (MR) spectroscopy. A matched muscle biopsy sample per mitted determination of mitochondrial volume density and the contribution o f the loss of mitochondrial content to the decline in oxidative capacity wi th age. 2. The maximal oxidative phosphorylation rate or oxidative capacity was est imated from the Per recovery rate constant (k(PCr)) and the [PCr] in accord ance with a simple electrical circuit model of mitochondrial respiratory co ntrol. Oxidative capacity was 50 % lower in the elderly vs. the adult group (0.61 +/- 0.04 vs. 1.16 +/- 0.147 mM ATP s(-1)). 3. Mitochondrial volume density was significantly lower in elderly compared with adult muscle (2.9 +/- 0.15 vs. 3.6 +/- 0.11%). In addition, the oxida tive capacity per mitochondrial volume (0.22 +/- 0.042 vs. 0.32 +/- 0.015 m M ATP (s %)(-1)) was reduced in elderly vs. adult subjects. 4. This study showed that elderly subjects had nearly 50 % lower oxidative capacity per volume of muscle than adult subjects. The cellular basis of th is drop was a reduction in mitochondrial content, as well as a lower oxidat ive capacity of the mitochondria with age.