Volitional step execution is an ineffective predictor of recovery performance after sudden balance loss across the age range

Rapid stepping to preserve stability is a crucial action in avoiding a fall. It is also an important measure in the assessment of fall-resisting skills. We examined whether volitional step execution correlates with recovery stepping performance after sudden balance loss for adults of different ages. In addition, we investigated whether volitional step performance can discriminate between individuals with high and low balance recovery capabilities, i.e. between those making single versus multiple steps after balance perturbation. Healthy adults (28 young, 43 middle-aged and 26 older; 24 ± 4, 52 ± 5 and 72 ± 5 years respectively) performed a single step in the anterior direction volitionally in response to a mechanical stimulus to the heel. In a second stepping task, participants experienced sudden anterior balance loss in a lean-and-release protocol. For both tasks, an optical motion capture system was used to assess stepping kinematics. We found on average 28% shorter reaction times, 46% faster maximal step velocities and 48% higher rates of increase in base of support across all participants after sudden balance loss compared to volitional stepping (p < 0.001). There was a significant age-related decline in recovery stepping performance after sudden balance loss: 24/26 older, 15/43 middle-aged and none of the younger adults required two or more steps to regain balance (p < 0.001). Multiple- compared to single-steppers had on average 23% shorter step lengths and 12% lower maximal step velocities for the lean-and-release task (p < 0.01). Multiple-steppers also had reduced rates of increase in base of support for both stepping tasks (14% for balance recovery and 11% for volitional stepping). Furthermore, in examining the relationship between the results of the two tasks, only weak to moderate correlations were observed for step velocity and rate of increase in base of support (0.36 ≤ r ≤ 0.52; p < 0.001). Thus, performance in volitional step execution has a low potential to explain variability in recovery response after sudden balance loss in adults across the lifespan and hence seems less suitable to be used to identify deficiencies in reactive stepping responses necessary to cope with sudden balance disturbances.