Figure 1. Set-up and design.

A, subjects flexed the thumbs to press down on a lever and lift weights suspended out of sight. A constant 500 g lifted by the reference hand was matched by adjusting the weight lifted by the indicator hand. Weight-matching tests were performed before and after conditioning the lifting muscle of the reference limb, with minimal delay between testing and conditioning. B–D, five conditioning protocols were tested: B, high-force fatigue in which the subject made a maximum isometric contraction until force had fallen to 40% of the initial maximum; C, low-force fatigue with the 40% contraction maintained until it could not be sustained; D, after a prolonged period of complete paralysis with rocuronium and then allowing the muscle to recover maximal force output to 40% of the initial level. Test times differ between subjects and between conditions B, C and D.