Mitochondrial Dysfunction Impacts Exercise Efficiency In The Elderly

Abstract

Reduced efficiency of mitochondrial generation of ATP from O2 is expected to lower leg power output per O2 uptake (i.e., exercise efficiency). PURPOSE: Here we test the impact of mitochondrial inefficiency in human quadriceps muscle (i.e., loss of phosphorylation capacity per mitochondrial content (ATPmax/Vv[mt,f] with age; J Physiol. 526.1: 203, 2000) on exercise efficiency of the elderly. METHODS: Mitochondrial coupling efficiency (ATP/O2) was determined from ATPmax/Vv[mt,f] using the maximum O2 uptake per mitochondrial content. Oxygen uptake and leg power output were elicited by cycle ergometer exercise. RESULTS: Lower mitochondrial coupling was found in elderly (4.3+0.3 SE, n=31; mean age = 69 yrs) vs. adult muscle (mean, 6.0+0.6, n=5; mean age = 39 yrs). Cycle ergometer exercise revealed a reduced exercise efficiency (delta efficiency: change in power output/change in O2 uptake) of cycling in elderly (22+1%; n=40) vs. adult (27+1%; n=9) groups. Contractile-coupling efficiency calculated from mitochondrial and exercise efficiency agreed with literature values (∼50-70%; J Physiol 586.7: 1993, 2008) but no difference was found between the elderly (54+3%) and adult (49+5%) groups. CONCLUSIONS: A reduced coupling of ATP supply from O2 uptake appears to be the basis of the lower delta efficiency in the elderly. These results indicate that mitochondrial dysfunction impacts exercise efficiency and may be a key part of the loss of exercise performance with age.