Pd. Chilibeck et al., MUSCLE CAPILLARIZATION, O-2 DIFFUSION DISTANCE, AND VO(2) KINETICS INOLD AND YOUNG INDIVIDUALS, Journal of applied physiology, 82(1), 1997, pp. 63-69
The relationships between muscle capillarization, estimated O-2 diffus
ion distance from capillary to mitochondria, and O-2 uptake (VO2) kine
tics were studied in 11 young (mean age, 25.9 yr) and 9 old (mean age,
66.0 yr) adults. VO2 kinetics were determined by calculating the time
constants (tau) for the phase 2 VO2 adjustment to and recovery from t
he average of 12 repeats of a 6-min, moderate-intensity plantar flexio
n exercise. Muscle capillarization was determined from cross sections
of biopsy material taken from lateral gastrocnemius. Young and old gro
ups had similar VO2 kinetics (tau VO2-on 44 vs. 48 s; tau VO2-off = 33
vs. 44 s, for young and old, respectively), muscle capillarization, a
nd estimated O-2 diffusion distances. Muscle capillarization, expresse
d as capillary density or average number of capillary contacts per fib
er/average fiber area, and the estimates of diffusion distance were si
gnificantly correlated to VO2-off kinetics in the young (r = -0.68 to
-0.83; P < 0.05). We conclude that I) capillarization and VO2 kinetics
during exercise of a muscle group accustomed to everyday activity (e.
g., walking) are well maintained in old individuals, and 2) in the you
ng, recovery of VO2 after exercise is faster, with a greater capillary
supply over a given muscle fiber area or shorter O-2 diffusion distan
ces.