Figure 1

Exemplar trial where the left arm is responding to being perturbed into shoulder extension. (a) Hand speed over time. Hand speed minimum representing the end of the hand’s initial deceleration is shown by the circle marker. (b) Joint velocity of the loaded joint (shoulder, thick line) and the non-loaded joint (elbow, thin line) over time. Joint flexion is positive and joint extension is negative. The initial velocity extrema of the elbow and shoulder joint are marked by the circle markers, labelled ‘E’ and ‘S’ respectively. The offset is the time between these points. (c) Left: Schematic of arm orientation and perturbation direction for the trial presented in this figure. Right: Participant’s hand path after perturbation onset. The visual target and the hand path are shown in black. The initial velocity extrema of the elbow and shoulder joint are marked by the circle markers, labelled ‘E’ and ‘S’ respectively. The X marker indicates the maximum displacement of the hand (which in this case corresponded to the deceleration time- circle marker). Return time occurred when subject returned within 1 cm of their endpoint location (dot marker indicated to occur at 2200 ms). Endpoint (the position at the end of the trial) is indicated by square marker and endpoint error is the distance between this point and the centre of the visual target.