Ageing, muscle properties and maximal O(2) uptake rate in humans

Abstract

This paper asks how the decline in maximal O(2) uptake rate (VO(2),max) with age is related to the properties of a key muscle group involved in physical activity - the quadriceps muscles. Maximal oxygen consumption on a cycle ergometer was examined in nine adult (mean age 38.8 years) and 39 elderly subjects (mean age 68.8 years) and compared with the oxidative capacity and volume of the quadriceps. VO(2),max declined with age between 25 and 80 years and the increment in oxygen consumption from unloaded cycling to VO(2),max (delta VO(2)) in the elderly was 45 % of the adult value. The cross-sectional areas of the primary muscles involved in cycling - the hamstrings, gluteus maximus and quadriceps - were all lower in the elderly group. The quadriceps volume was reduced in the elderly to 67 % of the adult value. Oxidative capacity per quadriceps volume was reduced to 53 % of the adult value. The product of oxidative capacity and muscle volume - the quadriceps oxidative capacity - was 36 % of the adult value in the elderly. Quadriceps oxidative capacity was linearly correlated with delta VO(2) among the subjects with the slope indicating that the quadriceps represented 36 % of the VO(2) increase during cycling. The decline in quadriceps oxidative capacity with age resulted from reductions in both muscle volume and oxidative capacity per volume in the elderly and appears to be an important determinant of the age-related reduction in delta VO(2) and VO(2),max found in this study.

Figures

Figure 1. Maximal oxygen uptake rate (V̇O2,max) as a function of age

□, adult subjects; ▪, elderly subjects. The regression equation for all subjects is: y = -44.1 x = 4724.6, r2 = 0.42.

Figure 2. Quadriceps volume (VQ) as a function of age

Symbols as in Fig. 1. The regression equation for all subjects is: y = - 37.4 x = 4973 (r2 = 0.28).

Figure 3. Quadriceps cross-sectional area as a function of the sum of the cross-sectional areas of the quadriceps, gluteus and hamstring muscles

Symbols as in Fig. 1.

Figure 4. Quadriceps oxidative capacity as a function of age

Symbols are as in Fig. 1. The regression equation for all subjects is: y = -0.086 x = 7.498 (r2 = 0.44).

Figure 5. Quadriceps oxidative capacity as a function of the increment in oxygen consumption between unloaded cycling and V̇O2,max (ΔV̇O2)

Symbols are as in Fig. 1. The regression equation for all subjects is: y = 0.36 x– 46.97 (r2 = 0.57).

Figure 6. Change in muscle properties between adult (□) and elderly (▪) groups

A, decline in volume-specific oxidative capacity as the product of the loss of mitochondrial volume density (Vv(mt,f)) and of mitochondrial capacity (oxidative capacity/Vv(mt,f)). B, decline in whole muscle oxidative capacity as the product of loss of muscle volume (VQ) and volume-specific oxidative capacity (oxidative capacity/VQ).