Twenty healthy participants will be included in the trial that adopts a two-armed randomized, crossover design. With a washout-period of one week in between, each subject participates in two sessions in a randomised order. In both sessions, cervical ROM (flexion/extension, rotation, lateral flexion) will be measured twice (with a five-minute wait period). In all measurements, the zero position will be determined by means of a bulls eye spirit level. The difference of the two sessions consists in the design of the waiting period. In one session, the subjects will keep the mask carrying the ultrasound markers on their head. In the other session, the mask will be removed during the break.