Aerobic determinants of the decline in preferred walking speed in healthy, active 65- and 80-year-olds

The preferred walking speed is a common measure of mobility that declines with age and has been related to maximal oxygen uptake (O_2,max). The present study determined whether this decline is associated with a higher percentage of the ventilatory threshold in older adults walking at their preferred speed. We compared the preferred walking speed and O₂ at this speed in relation to both O_2,max and O₂ corresponding to the ventilatory threshold (T _VE) in healthy, physically active sexagenarians (G65, n=10) and octogenarians (G80, n=10) walking on a treadmill. The preferred walking speed was lower in G80 (1.16±0.09 m·s^–1) than in G65 (1.38±0.09 m·s^–1; P<0.001). Energy expenditure and the energy cost of walking at the preferred walking speed were not significantly different between the two groups. G80 subjects exhibited significantly higher fractions of O_2,max (60.8±8.0%) and T _VE (74.2±7.9%) at the preferred walking speed than G65 (42.9±5.0 and 53.2±5.7% respectively; P<0.001). Multiple regression analysis showed that the fraction of T _VE was the main determinant, with a small contribution of height, in the decline in the preferred walking speed in healthy and active elderly subjects (R ²=64%; P<0.001). These findings show that with age, walking at the preferred speed requires a higher fraction of T _VE. This increase in the relative physiological effort at preferred walking speed could explain the reduction in this gait speed in healthy older subjects.