Résumé
The preferred walking speed is a common measure of mobility that declines with age and has been related to maximal oxygen uptake (VO^sub 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 VO^sub 2^ at this speed in relation to both VO^sub 2,max^ and VO^sub 2^ corresponding to the ventilatory threshold (T^sub 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^sup -1^) than in G65 (1.38±0.09 m·s^sup -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 VO^sub 2,max^ (60.8±8.0%) and T^sub 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^sub 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^sup 2^=64%; P<0.001). These findings show that with age, walking at the preferred speed requires a higher fraction of T^sub VE^. This increase in the relative physiological effort at preferred walking speed could explain the reduction in this gait speed in healthy older subjects.[PUBLICATION ABSTRACT]