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

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 (ATP_max) 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 ATP_max per St3 respiration (ATP_max/St3).Results.In vitro St3 respiration was significantly correlated with in vivo ATP_max (r² =. 47, p =. 004). Total oxidative capacity of the quadriceps (St3*quadriceps contractile volume) was a determinant of VO₂ peak (r² =. 33, p =. 006). ATP_max (r² =. 158, p =. 03) and VO₂ peak (r² =. 475, p max/St3 and VO₂ peak in a multiple linear regression model improved the prediction of preferred walking speed (r² =. 647, p