Interaction between age and gait velocity in the amplitude and timing of antagonist muscle coactivation.

Old adults execute single-joint voluntary movements with heightened antagonist muscle coactivation and altered timing between agonist and antagonist muscles. It is less clear if old adults adopt similar strategies during the most common form of activity of daily living, gait, and if age and gait velocity interact. We compared antagonist muscle activation amplitude and onset, offset, and activation duration of the vastus lateralis, biceps femoris, tibialis anterior, and gastrocnemius lateralis from surface EMG in 17 young (age 19-25) and 17 old adults (age 71-85) while walking at 1.2, 1.5, and 1.8m/s. All participants were healthy and highly mobile. The activation level of the four muscles when each acted as the antagonist was, on the average, 83% higher in old vs young adults (for each muscle p<0.05). In two of four muscles this activation increased with gait velocity in young but not in old adults. The inter-burst interval between TA and GL was two-fold (83 ms) longer in young vs old adults and at higher gait velocities it became 14% (24 ms) shorter in young but 51% (31 ms) longer in old adults (interaction, p=0.015). It is concluded that there is an interaction between age and gait velocity in the amplitude and timing of antagonist muscle coactivation.