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Fig. 8. The COM mechanics occur along a continuum related to how well the limb supported body weight BW and whether it produced or absorbed net energy. Different symbols represent different `energy mode' categories. The GRF impulse magnitude and direction (|J| and {phi}) distinguish the different response patterns, as illustrated by their relationship with two energy ratios. (A) The vertical energy ratio ({Delta}EKv: {Delta}EP) strongly correlates with |J|, and indicates the level of BW support (0 indicates full BW support, 1.0 indicates free fall). We categorized trials in which the EV ratio ≥0.5 as `EKv' mode (dotted line). (B) The perturbation energy ratio ({Delta}Ecom: {Delta}EV) correlates with {phi}, and distinguishes energy redistribution vs actuation by the limb. A value of zero indicates that the {Delta}EV was converted to EKh ({Delta}EV->{Delta}EKh), with no net muscular work, consistent with spring-like limb function. A value of 1.0 indicates that all of {Delta}EV is absorbed, a value >1.0 indicates deceleration (-{Delta}EKh) and a value <0 indicates acceleration (+ {Delta}EKh). We categorized trials in which the perturbation energy ratio ≥0.5 as `Ecom' mode (dotted line).





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