Characteristic muscle activity patterns during gait initiation in the healthy younger and older adults

• The younger group had the more intra-subject CVs than older group.
• The co-contraction index was greater in older subjects than younger subjects.
• The more co-contraction of muscles was associated with smaller intra-subject CV.
• The findings suggest that muscle behaviors are altered in older adults during GI.

It is thought that gait initiation (GI) might be an optimal task for identifying postural control deficiencies. Thus, the aim of this study was to clarify the strategies adopted by older subjects during this task. 16 healthy younger and 15 healthy older adults participated in the study. Subjects were instructed to begin forward stepping with their dominant limb in response to an auditory stimulus. The mean muscle activity, co-contraction index, and intra-subject coefficients of variation (intra-subject CVs) of dominant limb muscles in different phases of GI were measured. The level of association between the co-contraction index and intra-subject CV of muscles was also explored. This study showed that in the anticipatory phase, the younger group had larger amplitudes and more intra-subject CVs than older the group, particularly for the tibialis anterior muscle. However, the co-contraction index was greater in older subjects relative to younger subjects. During the weight transition phase, tibialis anterior, semitendinosus and vastus lateralis muscles of older adults had a lower amplitude as compared to younger adults. However, during the locomotor phase, the activity of tibialis anterior was greater in comparison to younger adults. Also, during this phase, similar to the anticipatory phase, the co-contraction index between tibialis anterior and gastrocnemius muscles was greater in older subjects relative to younger subjects. Additionally, the larger co-contraction index of some muscles was associated with smaller intra-subject CV. These findings suggest that muscle behaviors are altered with aging and older adults employ different strategies in the different phases of GI as compared to younger adults.