Can increasing footwear bending stiffness ameliorate age-related mechanical and metabolic deficits in walking?

Older adults consume metabolic energy faster than their younger adult counterparts while walking, particularly on sloped terrain. This increased rate is likely in part due to an age-related shift in moment and power production from the ankle joint to the hip. Shifting these mechanics proximally may occur due to older adults losing more mechanical energy at the foot and producing lower ankle joint moments, deficits that are exaggerated when walking uphill or against impeding forces. A promising method to target some of these foot and ankle mechanics differences is increasing footwear longitudinal bending stiffness via carbon fiber insoles. We examined how increasing footwear stiffness alters older adult (9F/10M, 70 ± 5.9 yrs) walking energetics across slopes. Increasing footwear stiffness reduced the magnitude of negative power from the foot+shoe structures distal to the forefoot, but increased negative power of the foot+shoe structures distal to the hindfoot (foot+shoe complex as a whole). At the ankle, peak joint moment increased by ∼10% in the stiffest footwear compared with the baseline standardized shoe. Neither knee and hip mechanics nor net metabolic power were consistently affected by footwear stiffness. These results indicate that increasing older adult footwear stiffness via flat carbon fiber insoles attenuates some age-related deficits in foot and ankle mechanics, but does not result in a clear attenuation of the age-related distal to proximal shift in joint mechanics or clear metabolic benefits. The increase in ankle joint moment with stiffer footwear could be useful longer-term as a means to strengthen the calf musculature of older adults. Future work should examine the effects of footwear stiffening on ankle muscle-level outcomes such as force production, excitation, and fascicle mechanics.