Mitochondrial oxidative capacity and coupling: effects of aging and exercise training

Abstract

Aging is associated with decreased content and function of mitochondria. Exercise, particularly endurance exercise, stimulates mitochondrial biogenesis, providing an attractive aging countermeasure. The influence of aging and exercise on mitochondrial coupling (i.e., efficiency) is less well studied. We studied the effects of 8 weeks of endurance (ET), resistance (RT), and combined (CT) training on oxidative capacity and coupling in 33 young (Y, 25±1y) and 27 older (O, 70±2y) adults. Mitochondria were isolated from muscle biopsies before and after intervention. State 3 respiration was measured with substrates for complex I, I+II, and II by high-resolution respirometry. Mitochondrial coupling was assessed from respiratory control ratios (RCR) and ADP:O ratios. Before training, respiration was lower in O than Y when expressed per g tissue or mg mito protein. RCR was similar in Y and O, but ADP:O was lower in O. ET and RT groups showed similar, modest increases in oxidative capacity, but the most robust increases were observed in CT in both age groups. Mitochondrial coupling was unaffected by training. These data indicate that 1) aging is associated with reduced mitochondrial capacity at the organelle level, 2) both Y and O exhibit the most profound increase in mitochondrial capacity with combined endurance and resistance training, and 3) age-related declines in mitochondrial coupling are not reversed by exercise.