Foot-Ankle Mechanical Transmission: Age Effects and the Relation to Ankle Push-Off During Walking.

Older adults walk with less push-off power than younger adults. Principally attributed to plantar flexor dysfunction, growing evidence implicates interactions between the foot and ankle as critical for generating effective push-off. Our purposes were to measure age effects on foot-ankle mechanical transmission (FAMT, ie, the ratio between metatarsal phalangeal extension and medial gastrocnemius fascicle length change), and its association with ankle push-off during walking. We hypothesized that (1) FAMT would be lesser in older adults and (2) lesser FAMT would positively correlate with slower preferred speeds and reduced ankle push-off intensity. Fourteen younger adults (25 [6] y) and 15 older adults (71 [5] y) participated. Older adults had 45% to 48% lesser FAMT than younger adults from 0° to 30° metatarsal phalangeal extension-an age-related difference that was not evident from 30° to 60° metatarsal phalangeal extension. However, we did not find any significant correlations with walking outcomes. Assuming our findings can be replicated in future studies and represent a genuine phenomenon of relevance to the biomechanics of aging gait, we suspect that compensations may be discovered in older adults to explain this lack of significance. Future work should include measures of muscle activities and foot mechanics during walking and/or perform more controlled comparisons at fixed speeds.