Cognitive influence on postural stability: A neuromuscular analysis in young and older adults

Background. Previous literature indicates that attentional resources are re quired for recovery of postural stability. previous studies have also exami ned the effect of aging on the performance of a static postural task while a secondary cognitive task is being conducted. This study describes the eff ect of a cognitive task on the neuromuscular response characteristics under lying reactive balance control in young versus older adults. Methods. The attentional demand on the neuromuscular system was examined in 14 young and 12 healthy older adults by analysis of the integrated electro myography activity while the adults were performing a dual-task paradigm. T he primary task involved standing platform perturbations and the secondary task was a math task that involved subtraction by threes. Integrated electr omyography activity was compared between the cognitive (math and balance) t ask versus control(balance only) task. Results. For both groups of subjects, onset latency of postural muscle resp onses did not change under dual-task conditions. In contrast, the amplitude of postural muscle activity was significantly affected by performance of a secondary task. When electromyography data were combined for both young an d older adults, there was a decrease in muscle response amplitude in both a gonist (gastrocnemius) and antagonist (tibialis anterior) muscles when the cognitive math task was performed. This was apparent at 350-500 millisecond s from plate onset for the gastrocnemius and between 150 and 500 for the ti bialis anterior. When young and older adults were compared, an age by task interaction effect was seen in muscle response amplitude for the agonist (g astrocnemius) muscle between 350 to 500 milliseconds. with older adults sho wing a significantly greater reduction than young adults. Conclusion. The decline of muscle activity when the secondary task was perf ormed suggests that less attentional processing capacity was available for balance control during the dual-task paradigm. The results also indicate th at the dual-task activity has a greater impact on balance control in the ol der adults than in the young adults.