Effects of concurrent cognitive task on pre-landing muscle response latency during stepping down activity in older adults with and without a history of falls

Purpose. To investigate the co-contraction of ankle muscles in older subjects with and without a history of falls during a stepping down activity, and whether the co-contraction was disrupted by a concurrent cognitive task. Method. Ten fallers and 9 non-fallers (mean age = 72.0 ± 5.0 and 72.1 ± 7.3 years, respectively) were recruited. Electromyography (EMG) of the tibialis anterior (TA) and medial gastrocnemius (MG) was recorded during stepping down with and without a concurrent cognitive task. Co-contraction was investigated using the time between the EMG onset and the foot touching a force-platform, termed the pre-landing muscle response latency. Results. The fallers showed longer pre-landing muscle response latencies in the TA compared with non-fallers (141.1 ± 58.1 ms and 110.9 ± 68.2 ms, respectively). With a concurrent cognitive task, the pre-landing muscle response latencies in the TA were shortened in fallers significantly more than in non-fallers (44.4% and 15.5%, respectively). No significant difference in MG activation was found between 2 groups in the stepping down activity with and without cognitive task. Conclusions. Subjects with history of falls exhibit a greater shortening in the pre-landing muscle response latency than non-fallers when distracted during stepping down. Disruption of their co-contraction in ankle joint might precipitate such older adults to fall.