Older adults produce joint moments less economically than young adults | Journal of Applied Physiology | American Physiological Society

Older adults expend more metabolic energy than young adults during walking (worse walking economy). Amid the numerous physiological changes that accompany advanced aging, the mechanisms governing the age-related decline in walking economy remain unestablished. Due to conflicting evidence, we studied whether older adults produce lower-limb joint moments less economically than young adults, independent of an age-related difference in muscle co activation. Eight older adults (71.6 ± 6.0 years) and 13 young adults (23.1 ± 4.7 years) repeatedly produced hip and ankle moment cycles on a dynamometer following visual feedback and an audible metronome. We instructed participants to produce moments with peak net torque values of 20 and 30 Nm at a 0.75 Hz cycle frequency and a 0.5 duty cycle. Overall, young and older adults did not co-activate their antagonist muscles differently during the moment production trials. At the hip, older adults expended more metabolic power than young adults despite producing lower moment amplitudes. At the ankle, older adults expended more metabolic power than young adults while producing non-different moment production cycles. Because older adults produced lower-limb joint moments less economically than young adults, interventions aimed at prolonging youthful walking economy into advanced age may need to directly address changing muscle-tendon unit physiology.

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Functional Electrical Stimulation of the Soleus Redistributes Lower-Limb Joint Work Distally in Young and Older Adults | Journal of Applied Physiology | American Physiological Society

Older adults walk with reduced ankle and greater hip mechanical output compared to young adults. This “distal-to-proximal redistribution” likely contributes to the greater metabolic energy expenditure during walking in older versus young adults. Due to the inverse relationship between ankle and hip use, functional electrical stimulation (FES) of the ankle extensors may increase ankle mechanical work and indirectly decrease hip mechanical work. Although FES increases stimulated muscle metabolism, bilateral soleus stimulation may restore more youthful walking kinetics without a detectable change in whole-body metabolism because ankle extension requires less metabolic energy than hip extension. Ten young adults and 10 older adults walked on a treadmill at 1.25 m/s with and without FES bilaterally applied over the respective leg’s soleus when the anterior-posterior ground reaction force exceeded +10% body weight. FES use altered walking mechanics and metabolic power similarly across age groups (all FES condition and age group interactions p≥0.214). Across age groups, FES increased ankle mechanical power (p=0.041) and redistributed mechanical work production to occur relatively more at the ankle and less at the hip (p=0.010). The lower-limb joint redistribution ratio of older adults walking with FES was not different to that of young adults during baseline (p=0.785). Moreover, walking with FES increased metabolic power by 2% (p=0.037). FES attenuated older adult distal-to proximal redistribution and modestly increased whole-body metabolic rate. Overall, FES applied to soleus muscles during walking affects users similarly across the lifespan, indicating that FES interventions ought to consider a person’s functional needs, regardless of age.

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