| Summary |
Neuromechanical function declines with age and the ability of old adults to complete activities of daily living (ADLs) diminishes. To complete ADLs, old adults alter their strategies of movement and compensate for neuromuscular dysfunctions. A central issue in aging research is to determine the nature and magnitude of adaptability of the neuromuscular system that is retained with age. To address this issue, we perturbed the neuromuscular system with an inertial load at the ankle during level walking and measured muscular responses in an effort to identify neuromuscular plasticity. The hypothesis was that old adults would display an altered pattern of muscle activation compared to young adults in response to an inertial loading at the ankle. The purpose of this study was to compare the muscle activation patterns of old and young adults in response to a loading perturbation during level walking. Ten healthy old adults age 79 and 12 young adults age 22 walked 5 times across a 10-m walkway at 1 5m/s with and without load and at 1.7m/s with the load. The loading perturbation was achieved by attaching a mass of 5% of the subject's body mass to both ankles. Surface electromyography (EMG) was recorded and analyzed from the Vastus Lateralis (VL), Medial Hamstring (MH) and Lateral Hamstring (LH) during the swing and stance phases of the gait cycle and the Rectus Femoris (RF) EMG was also analyzed during the swing to stance and stance to swing transitions. Measures of plasticity included the intensity of muscle activation, expressed as a percent of maximal voluntary contraction, the time of muscle activity onset and the duration of muscle activity, expressed in milliseconds. Old adults activated their muscles more strongly than young adults in all conditions. Also, old adults increased activation of their VL (125%) and MH (120%) more than young adults during the swing phase of the gait cycle with mass added to the ankle (p<05). Old adults activated the MH (64ms) and LH (57ms) significantly earlier than young adults in response to the loading perturbation and also increased the duration of muscle activity in the VL (199ms), MH (154ms), LH (201ms) and RF (48ms) dunng the stance to swing transition (p<05). These alterations in neuromuscular activation patterns suggest that old adults responded differently than young adults when gait was perturbed by an inertial load at the ankle. It was concluded that old adults produce unique muscle activation patterns when gait is perturbed by inertial loading at the ankle to compensate for age associated neuromuscular dysfunctions. The implications of these findings is that the aging neuromuscular system is plastic, not hardwired and it has the capacity to reorganize its neuromechanical resources for successful execution of locomotor tasks. |
