Fig. 1

Custom-made testing device. When the participant sits upright on the chair included in the custom-made testing device, their back touches the moveable, individually fixable backrest (B), which allows us to adapt the distance between hand palm and trunk to reach 45° (C) or 90° (D) elbow flexion and a shoulder flexion of 8° ± 8.6° or 31° ± 7.5° (mean ± std) long or short muscle length, respectively. The device is adjustable in height and is positioned in a way such that the participant’s shoulders are parallel to the floor, while the top edge of the device is placed under the armpit (A). The relaxed arm rests on a moveable board fixed at 45° shoulder abduction (A). At the level of the shoulder joint, a load cell is placed on the front edge of the device, on which the participant places their palm (C, D)