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 (VO2 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 (31)P 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 (r (2) = .47, p = .004). Total oxidative capacity of the quadriceps (St3*quadriceps contractile volume) was a determinant of VO2 peak (r (2) = .33, p = .006). ATPmax (r (2) = .158, p = .03) and VO2 peak (r (2) = .475, p < .0001) were correlated with preferred walking speed. Inclusion of both ATPmax/St3 and VO2 peak in a multiple linear regression model improved the prediction of preferred walking speed (r (2) = .647, p < .0001), suggesting that mitochondrial efficiency is an important determinant for preferred walking speed.


CONCLUSIONS
Lower mitochondrial capacity and efficiency were both associated with slower walking speed within a group of older participants with a wide range of function. In addition to aerobic capacity, lower mitochondrial capacity and efficiency likely play roles in slowing gait speed with age.
Department of Health and Physical Activity, University of Pittsburgh, Trees Hall Rm 134D, Allequippa St. and Darragh St., Pittsburgh, PA 15260, USA. pmc17@pitt.edu
Paul M
PM
Coen
Sharon A
SA
Jubrias
Giovanna
G
Distefano
Francesca
F
Amati
Dawn C
DC
Mackey
Nancy W
NW
Glynn
Todd M
TM
Manini
Stephanie E
SE
Wohlgemuth
Christiaan
C
Leeuwenburgh
Steven R
SR
Cummings
Anne B
AB
Newman
Luigi
L
Ferrucci
Frederico G S
FG
Toledo
Eric
E
Shankland
Kevin E
KE
Conley
Bret H
BH
Goodpaster
D000367:Age Factors; D000368:Aged; D001706:Biopsy; D004734:Energy Metabolism / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008931:Mitochondria, Muscle / Q000378:metabolism*; D009119:Muscle Contraction / Q000502:physiology*; D018482:Muscle, Skeletal / Q000378:metabolism*; D010101:Oxygen Consumption / Q000502:physiology; D010807:Physical Endurance / Q000502:physiology*; D010809:Physical Fitness / Q000502:physiology; D004856:Postural Balance / Q000502:physiology; D052097:Quadriceps Muscle / Q000378:metabolism / Q000473:pathology; D016138:Walking / Q000502:physiology*