Fig. 1

Robotic assessment of the highest force for a given maximal intended force task. The two steps during the maximal intended force exertion of the performer are denoted both in the generic length-tension relationship (a) and time-force relationship during the robotic assessment of peak force (b). Step 1: the performer reaches isometric peak force (IPF) during an all-out effort at short (30% of peak range of motion) muscle-tendon length against the rigid and fixed robot arm. Attaining isometric peak force may take up to several seconds (2.5 s in this example), depending among other things on the magnitude of the attained force. Step 2: Immediately after attaining the individual’s IPF (automatically detected by the robot), the robot smoothly increases its force in the opposite direction while the performer tries to brake the movement of the robot arm. As the robotic force increases, the performer needs to increase the lengthening velocity (Step 2, A) in order to accomodate for the increased robotic force until the point is reached, where the force is velocity-independent (force plateau, P). For safety reasons, the range of motion for the pliometric action should be strictly controlled (to 60% of peak range of motion). Isometric, maximal intended isometric muscle action against fixed-position robotic exoskeleton; Pliometric, maximal intended pliometric muscle action against the robot-imposed force increase above IPF