Decrease in force control among older adults under unpredictable conditions

Shunsuke Ebisu

doi:10.1016/j.exger.2021.111649

2022-02-01

DOI：10.1016/j.exger.2021.111649

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Objectives: Falls in older adults generally occur during unpredictable situations. Controlling posture through finetuned muscle force before and after falls is necessary to avoid serious injuries. However, details regarding force control among older adults during unpredictable situations are unclear. This study determined the features of force control in a random force-tracking task among older adults. Methods: Ten healthy older adults (67-76 years) and eight healthy young adults (20-23 years) participated in three force-tracking tasks with ankle plantar flexion: low-range (LR), high-range (HR), and pseudo-random (PR) force tasks. Force control ability was assessed using the root mean square error (RMSE) between the target and muscle forces produced by the participants. Muscle activities from the lateral head of the gastrocnemius and the tibialis anterior during each task were measured using surface electromyography to calculate the co-contraction index (CCI). Results: In all tasks, older adults (RMSEs: 1.09-3.70, CCIs: 29.4-56.4) had a significantly greater RMSEs and CCIs than young adults (RMSEs: 0.49-1.83, CCIs: 11.7-20.6; all, p < 0.05). The RMSEs during force generation were significantly greater than those during force release (LR: p < 0.01, HR: p 0.05), except for the random forcetracking task in older adults. CCIs during the force release phase in both groups (older adults: 27.8-56.4, young adults: 15.0-20.6) were consistently greater than those during force generation (older adults: 24.5-50.4, young adults: 11.7-17.2). CCIs in force-tracing tasks differed in older adults, whereas those in the random force-tracing task increased. RMSEs and CCIs in the random and LR force-tracing tasks were significantly negatively correlated with the functional reach test (all: r 0.5, p < 0.05). Conclusion: Force control in older adults declines in low-band and random muscle force output. Moreover, increased CCIs in older adults are particularly pronounced during unpredictable situations.

Keyword:

Aging

Ankle muscles

Electromyography

Muscle strength

Motor control