Superposition principle applies to human walking with two simultaneous interventions

Abstract

Gait rehabilitation therapies provide adjusted sensory inputs to modify and retrain walking patterns in an impaired gait. Asymmetric walking is a common gait abnormality, especially among stroke survivors. Physical therapy interventions using adaptation techniques (such as treadmill training, auditory stimulation, visual biofeedback, etc.) train gait toward symmetry. However, a single rehabilitation therapy comes up short of affecting all aspects of gait performance. Multiple-rehabilitation therapy applies simultaneous stimuli to affect a wider range of gait parameters and create flexible training regiments. Understanding gait responses to individual and jointly applied stimuli is important for developing improved and efficient therapies. In this study, 16 healthy subjects participated in a four-session experiment to study gait kinetics and spatiotemporal outcomes under training. Each session consisted of two stimuli, treadmill training and auditory stimulation, with symmetric or asymmetric ratios between legs. The study hypothesizes a linear model for gait response patterns. We found that the superposition principle largely applies to the gait response under two simultaneous stimuli. The linear models developed in this study fit the actual data from experiments with the r-squared values of 0.95 or more.

Interference and Motor Memory Consolidation Effects of Sequential Gait Interventions: A randomized controlled trial

“…The coe cients corresponding to the second perturbation revealed that approximately 85% of the contribution of the constituent intervention could be predicted from the control interventions. This is a close approximation of the coe cients determined in a previous study that applied the same interventions simultaneously [32]. In addition, coe cients representing the impact of the rst intervention on acquired asymmetry during adaptation-2 were signi cantly (and predictably) smaller.…”

“…The previous ARAC study found that adaptation to SBT and ARAC exhibit additive effects in spatiotemporal and kinetic gait parameters when both therapies were applied simultaneously [32]. This superposition indicates that the adaptation mechanisms (i.e., "sensorimotor feedback" and "strategic") associated with these interventions are likely to run concurrently, allowing the participant to simultaneously bene t from the two interventions.…”

“…The relative contributions of SBT and ARAC in the acquisition of gait asymmetry during adaptation-2 were obtained using a linear model, similar to a previous study that examined the effects of two therapies used simultaneously [32]. Gait parameters included step length, step time, and vertical reaction force.…”

“…In addition to enhanced generalizability associated with rhythmic cueing, this form of training is also understood to encourage neuroplasticity, which also facilitates motor learning [28,29,30,31]. Rhythmic cueing has also been applied asymmetrically by assigning unequal step times for the left and right lower limbs [32]. The asymmetric rhythmic auditory cues (ARAC) partially simulate the asymmetry of SBT training using explicit cues that instruct participants to adjust the timing of their steps.…”

Real-time feedback control of split-belt ratio to induce targeted step length asymmetry

“…The ability to predict a patient's response to the training session (session two) allows for informed decisions to be made upon completion of the evaluation session (session one). Not all participants respond to all forms of gait intervention, as has been demonstrated in rhythmic cueing experiments for step time rehabilitation [13]. Therefore, this predictive model could potentially give examiners the ability to identify possible split-belt training non-responders quickly.…”