Time dependence of coupling in frequency-scaled bimanual coordination

Ankle control differentiation as a mechanism for mobility limitations

Independent control of the right and left ankles (differentiation) may be a motor control mechanism linking impaired coordination and mobility limitations. We tested the hypotheses that motor control differentiation of the ankles, as measured using Cross-Sample Entropy, during antiphase coordination at two movement frequencies, is associated with impaired coordination (high ankle coordination variability) and mobility limitations (Short Physical Performance Battery score ≤9). We conducted a cross-sectional study of community-dwelling older adults (N = 133) aged 80.04 (±4.67) years. In linear regression modeling, low ankle Cross-Sample Entropy (low motor control differentiation) was associated with poor (i.e., high) coordination variability at the slower (P = 0.026), but not the faster (P = 0.447), ankle movement frequency. In logistic regression modeling, low Cross-Sample Entropy at the slower (OR = 1.67; 95 % CI: 1.07-2.59) and faster (OR = 2.38; 95 % CI: 1.43-3.94) ankle movement frequencies were associated with increased odds for mobility limitations. Our findings support the hypothesis that ankle differentiation may be a motor control mechanism that links impaired coordination with mobility limitations.

Dimensionality in rhythmic bimanual coordination

Newell and Vaillancourt (2001) hypothesized that the dimensionality of motor behavior is a function of the level of task performance and the task dynamic. The present study examined high (in-phase), moderate (antiphase) and low (45°, 90°, and 135° relative phase) levels of task performance in bimanual coordination. Estimates of dimensionality were calculated for the component (effector movements), coupling of components (coupling of effectors), and task output (the produced relative phase) levels of analysis. The in-phase coordination mode had lower Approximate Entropy within, and lower Cross-Approximate Entropy between, effector movements than all other modes. The in-phase mode had higher relative phase Approximate Entropy than all other modes. These findings indicate lower effector and coupling dimensionality, and higher relative phase dimensionality, in the in-phase mode. These results support the hypothesis that at the levels of analysis with limit-cycle dynamics high levels of task performance are characterized by lower dimensionality than lower levels of performance. The results also support the hypothesis that high task performance of the fixed-point task goal of maintaining a constant relative phase is characterized by higher dimensionality than low level performance. Together, these findings support and generalize the Newell and Vaillancourt hypothesis to the component, coupling, and task output levels of analysis.