Abstract
Age-related reduction in muscle force generation capacity is similarly evident across different lower limb muscle groups, yet decline in locomotor performance with age has been shown to depend primarily on reduced ankle extensor muscle function. To better understand why ageing has the largest detrimental effect on ankle joint function during locomotion, we examined maximal ankle and knee extensor force development during a two-leg hopping test in older and young men, and used these forces as a reference to calculate relative operating efforts for the knee and ankle extensors as participants walked, ran and sprinted. We found that, across locomotion modes in both age groups, ankle extensors operated at a greater relative effort compared to knee extensors; however, slightly less pronounced differences between ankle and knee extensor muscle efforts were present among older men, mainly due to a reduction in the ankle extensor force generation during locomotion modes. We consider these findings as evidence that reduced ankle push-off function in older age is driven by a tendency to keep ankle extensor effort during locomotion lower than it would otherwise be, which, in turn, may be an important self-optimisation strategy to prevent locomotor-induced fatigue of ankle extensor muscles.
Highlights
Age-related reduction in muscle force generation capacity is evident across different lower limb muscle groups, yet decline in locomotor performance with age has been shown to depend primarily on reduced ankle extensor muscle function
High relative effort values may have been the result of a different joint moment definition methods between gait versus maximum reference force measurements[14]
Compared to the young men, older men walked with a similar self-selected speed (1.6 m/s) and exhibited a tendency towards a distal-to-proximal shift in muscular contributions, evident as a 8% lower ankle extensor force (p = 0.13, ES = 0.61) but a 6% greater knee extensor force (p = 0.27, ES = 0.46) (Fig. 1, Table 1)
Summary
Age-related reduction in muscle force generation capacity is evident across different lower limb muscle groups, yet decline in locomotor performance with age has been shown to depend primarily on reduced ankle extensor muscle function. Age-related force deficit has been shown to occur across all major locomotor muscle groups[1,2], decline in locomotor ability with age depends primarily on compromised ankle extensor muscle function This is evident from numerous studies showing that older adults compared to younger adults walk and run with reduced ankle extensor moment and power generation while exhibiting little or no declines in the muscular output of more proximal lower limb muscle groups[3,4,5,6,7,8]. An additional and more direct method for determining muscle effort is to use the same inverse dynamics method in the locomotor task and the force reference test
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