Fig. 7.
Results of an exploratory post hoc analysis of the association between motor module complexity (i.e., # of modules) and previously published values of local dynamic instability, quantified using short-term maximum divergence exponents (λs, 0–1 stride) (Qiao et al. 2018b). We refer the reader to the original manuscript for a detailed description of our data reduction and analysis procedures. Briefly, in that paper, we used a state space constructed from the 3-dimensional velocity of subject’s 7th cervical vertebrae and their time-delayed copies to compute maximum rates of divergence of initially neighboring trajectories. There, larger values of λs signify larger local dynamic instability. We concluded there that, compared with their effects in young adults, optical flow perturbations were capable of revealing independent effects of aging and a history of falls on gait instability that are not otherwise apparent during normal, unperturbed walking. Here, we performed 2 linear regressions across our study cohort: 1 during normal, unperturbed walking (A) and 1 in the presence of the largest amplitude optical flow perturbations used in this study (B; i.e., 50 cm). Our findings reveal that individuals with less motor module complexity in this study (namely, older adults with a history of falls) had larger local dynamic instability in the presence of optical flow perturbations (r2 = 0.22, P = 0.007) but not during normal, unperturbed walking (r2 = 0.06, P = 0.163). This outcome provides additional evidence that a reduced motor repertoire in older adult fallers may be a constraint on their ability to appropriately respond to balance challenges during walking: the major finding of our present study.