The kinematics and strategies of recovery steps during lateral losses of balance in standing at different perturbation magnitudes in older adults with varying history of falls

Abstract

Background Step-recovery responses are critical in preventing falls when balance is lost unexpectedly. We investigated the kinematics and strategies of balance recovery in older adults with a varying history of falls. Methods In a laboratory study, 51 non-fallers (NFs), 20 one-time fallers (OFs), and 12 recurrent-fallers (RFs) were exposed to random right/left unannounced underfoot perturbations in standing of increasing magnitude. The stepping strategies and kinematics across an increasing magnitude of perturbations and the single- and multiple-step threshold trials, i.e., the lowest perturbation magnitude to evoke single step and multiple steps, respectively, were analyzed. Fall efficacy (FES) and self-reported lower-extremity function were also assessed. Results OFs had significantly lower single- and multiple-step threshold levels than NFs; the recovery-step kinematics were similar. Surprisingly, RFs did not differ from NFs in either threshold. The kinematics in the single-step threshold trial in RFs, however, showed a significant delay in step initiation duration, longer step duration, and larger center of mass (CoM) displacement compared with NFs and OFs. In the multiple-step threshold trial, the RFs exhibited larger CoM displacements and longer time to fully recover from balance loss. Interestingly, in the single-stepping trials, 45% of the step-recovery strategies used by RFs were the loaded-leg strategy, about two times more than OFs and NFs (22.5 and 24.2%, respectively). During the multiple-stepping trials, 27.3% of the first-step recovery strategies used by RFs were the loaded-leg strategy about two times more than OFs and NFs (11.9 and 16.4%, respectively), the crossover stepping strategy was the dominated response in all 3 groups (about 50%). In addition, RFs reported a lower low-extremity function compared with NFs, and higher FES in the OFs. Conclusions RFs had impaired kinematics during both single-step and multiple-step recovery responses which was associated with greater leg dysfunction. OFs and NFs had similar recovery-step kinematics, but OFs were more likely to step at lower perturbation magnitudes suggesting a more “responsive” over-reactive step response related from their higher fear of falling and not due to impaired balance abilities. These data provide insight into how a varying history of falls might affect balance recovery to a lateral postural perturbation. Trial registration This study was registered prospectively on November 9th, 2011 at clinicaltrials.gov ( NCT01439451 ).

The Effects of Bicycle Simulator Training on Anticipatory and Compensatory Postural Control in Older Adults: Study Protocol for a Single-Blind Randomized Controlled Trial

“…The best observational and kinematic measures to represent the reactive (compensatory) balance responses are: the single-step and multiple-step thresholds (observational parameters), and the first-step recovery initiation duration, first step duration, total balance recovery duration, and total CoM displacement (kinematic parameters) ( 14 ). All of these parameters have been previously found to be able to distinguish between younger and older adults ( 14 ) and fallers and non-fallers ( 15 ). The single-step threshold was previously shown to be an independent predictor of a future fall ( 16 – 21 ) and to reflect unsteadiness in reactive balance control among older adults with varying histories of falls ( 15 ).…”

“…All of these parameters have been previously found to be able to distinguish between younger and older adults ( 14 ) and fallers and non-fallers ( 15 ). The single-step threshold was previously shown to be an independent predictor of a future fall ( 16 – 21 ) and to reflect unsteadiness in reactive balance control among older adults with varying histories of falls ( 15 ). Moreover, excellent inter-observer reliability has been reported for single-step and multiple-step thresholds (ICC 2, 1 = 0.978 and ICC 2, 1 = 0.971, respectively; p < 0.001), and for first-step recovery initiation duration, first step duration, total balance recovery duration, and total CoM displacement (ICC 2, 1 =0.917, ICC 2, 1 =0.975, ICC 2, 1 =0.950, and ICC 2, 1 =0.918, respectively; p < 0.001) ( 14 ).…”

“…Because the aim of the study is to examine the effect of perturbation-based bicycle training on various aspects of balance control, well-known parameters that reflect reactive, proactive, and standing postural balance control were selected. Calculations were performed separately to determine sample size requirements based on a single-step threshold in standing (reactive balance), voluntary step execution (i.e., foot contact time) (proactive balance), and ML postural sway (standing postural control), all reflective of unsteadiness in balance control between older and younger adults ( 13 , 14 , 50 , 55 , 58 , 67 , 68 ) and between fallers and non-fallers ( 13 , 15 – 21 , 55 – 58 , 60 ). Type I error probability of 0.05 and Type II error probability of 0.2 was applied for the three two-sided test calculations.…”

“…Fixed base-of-support (BoS) strategies (feet remaining in place) are used to restore balance with ankle, hip, trunk, and arm movements during minor-to-moderate unexpected perturbation magnitudes, whereas at larger balance perturbations, change of BoS strategies such as a stepping response are used ( 9 ). When balance is unexpectedly lost, a quick reactive step can prevent a fall from occurring ( 9 ); however, it was also found that hip, trunk, and arm movements are also part of reactive stepping reactions ( 9 , 12 – 15 ). A recent laboratory study of 83 older adults with varying histories of falls who were exposed to a wide range of perturbation magnitudes found that about 61% of these resulted in fixed BoS balance reactions without the need to recover balance by stepping ( 15 ).…”

“…When balance is unexpectedly lost, a quick reactive step can prevent a fall from occurring ( 9 ); however, it was also found that hip, trunk, and arm movements are also part of reactive stepping reactions ( 9 , 12 – 15 ). A recent laboratory study of 83 older adults with varying histories of falls who were exposed to a wide range of perturbation magnitudes found that about 61% of these resulted in fixed BoS balance reactions without the need to recover balance by stepping ( 15 ). In fact, by using hip, trunk, and arm movements, the older adults were able to decelerate the center of mass (CoM) movement over the BoS, which may result in an ability to perform balance recovery steps at a higher perturbation magnitude, i.e., higher step threshold.…”