Skeletal muscle mitochondrial energetics are associated with maximal aerobic capacity and walking speed in older adults

Abstract

Background.Lower ambulatory performance with aging may be related to a reduced oxidative capacity within skeletal muscle. This study examined the associations between skeletal muscle mitochondrial capacity and efficiency with walking performance in a group of older adults.Methods.Thirty-seven older adults (mean age 78 years; 21 men and 16 women) completed an aerobic capacity (VO 2 peak) test and measurement of preferred walking speed over 400 m. Maximal coupled (State 3; St3) mitochondrial respiration was determined by high-resolution respirometry in saponin-permeabilized myofibers obtained from percutanous biopsies of vastus lateralis (n = 22). Maximal phosphorylation capacity (ATPmax) of vastus lateralis was determined in vivo by 31P magnetic resonance spectroscopy (n = 30). Quadriceps contractile volume was determined by magnetic resonance imaging. Mitochondrial efficiency (max ATP production/max O2 consumption) was characterized using ATPmax per St3 respiration (ATPmax/St3).Results.In vitro St3 respiration was significantly correlated with in vivo ATPmax (r2 =. 47, p =. 004). Total oxidative capacity of the quadriceps (St3*quadriceps contractile volume) was a determinant of VO2 peak (r2 =. 33, p =. 006). ATPmax (r2 =. 158, p =. 03) and VO2 peak (r2 =. 475, p