Fig 1. Experimental set-up and raw trial recordings in a subject for each situation.

(A, left) Imposed unloading situation: the load was released at unpredictable times by the experimenter. (A, middle) Voluntary unloading situation: the load was lifted by the subject, using the right hand. (A, right) Learning situation: the lifting of the load from the platform by the subject’s right hand triggered the unloading of the load suspended below the left forearm. (B) Parameters recorded are as follows, from top to bottom: force, elbow rotation angle, EMG of the biceps brachii and the triceps brachii on the postural forearm. The decrease of the force indicated the onset of unloading (vertical line), used as a reference time. During the imposed unloading situation (B, left), note the upward elbow rotation and the decreased activity on the biceps brachii, which corresponds to the unloading reflex. During the voluntary unloading situation (B, middle), note the reduced elbow rotation and the early biceps brachii inhibition before unloading. During the learning situation (B, right), the force decreased occurring when the subject lifted the object (F1) is depicted by a dashed trace, and is followed by the release of the load suspended below the forearm (F2). The progressive reduction of the elbow rotation amplitude reflects the improvement of the postural stabilization. On this particular trial, a double inhibition pattern was found on the biceps brachii. (Reprinted from under a CC BY license, with permission from Elsevier, original copyright 2012).