Corticospinal drive is associated with temporal walking adaptation in both healthy young and older adults

Abstract

Healthy aging is associated with reduced corticospinal drive to leg muscles during walking. Older adults also exhibit slower or reduced gait adaptation compared to young adults. The objective of this study was to determine age-related changes in the contribution of corticospinal drive to ankle muscles during walking adaptation. Electromyography (EMG) from the tibialis anterior (TA), soleus (SOL), medial, and lateral gastrocnemius (MGAS, LGAS) were recorded from 20 healthy young adults and 19 healthy older adults while they adapted walking on a split-belt treadmill. We quantified EMG-EMG coherence in the beta-gamma (15–45 Hz) and alpha-band (8–15 Hz) frequencies. Young adults demonstrated higher coherence in both the beta-gamma band coherence and alpha band coherence, although effect sizes were greater in the beta-gamma frequency. The results showed that slow leg TA-TA coherence in the beta-gamma band was the strongest predictor of early adaptation in double support time. In contrast, early adaptation in step length symmetry was predicted by age group alone. These findings suggest an important role of corticospinal drive in adapting interlimb timing during walking in both young and older adults.

Walking speed does not affect age-differences in ankle muscle beta-band intermuscular coherence during treadmill walking

“…As expected, we observed ~50% age-related reductions in beta coherence between synergistic ankle muscle pairs (Figure 1). Such reductions agree with previous data 13,14,18 , suggesting that age affects the organization of synaptic input to the motoneuron pools. Weak intermuscular beta coherence for the ankle muscles may imply that output from the motor centers is sub-optimal.…”

“…As we hypothesized that modulation in intermuscular beta coherence with walking speed would occur in an age-specific manner (low to no modulation in coherence in older vs. younger), it is also unexpected that age and walking speed did not interact. However, while unexpected, previous evidence also suggested that changes in walking speed did not affect and did not interact with aging in inducing modulation in intermuscular coherence 13 . Different from frequency domain outcomes (as coherences), muscle activation as measured by EMG amplitude indicated a lack of modulation in coactivation in older vs. younger individuals as the walking speed increases 12 .…”

“…Based on lesion data in neurological patients, intermuscular beta coherence at 15-35 Hz emanates from cortical structures 19 , which are known to contribute to gait control [16][17][18][19] . Intra/intermuscular beta coherence of synergistic lower extremity muscles measured during walking seems to decrease with age 13,14,18 . However, it is unknown if age and speed each differently affect beta coherence during walking.…”

“…Although age-effects on walking speed have been thoroughly examined [8][9][10][11] , the mechanisms underlying age-typical reductions in the capacity to modulate neuromuscular control with changes in walking speed have not yet been fully elucidated. Such information could be insightful because age can affect locomotor muscle activation in the amplitude but also in the frequency domain [12][13][14] . For instance, while aging was related to an increase in muscle coactivation during walking (accompanied by ~20% higher energy cost of transport in older individuals) 15 , the rate of change in coactivation due to walking speed was substantially lower in older vs. younger individuals 12 .…”

“…We hypothesized an interaction between age and walking speed in beta coherence so that older vs. younger individuals would have lower coherence without modulating it with walking speed. We based this expectation on a lack of age-related modulation in beta coherence during walking after muscle fatigue 14 and split-belt perturbations 13 . Our walking speed data would extend these previous data suggesting potentially a general age-related impairment in the neural control of walking.…”