Myofascial force transmission between the ankle and the dorsal knee: A study protocol

BACKGROUND: Connective tissue links the skeletal muscles, creating a body-wide network of continuity. A recent in-vivo experiment demonstrated that passive elongation of the calf caused a caudal displacement of the semimembranosus muscle, indicating force transmission across the dorsal knee joint. However, it remains unclear as to whether this observation is dependent on the joint angle. If force would not be transmitted at flexed knees, this would reduce the number of postures and movements where force transmission is of relevance. Our trial, therefore, aims to investigate the influence of passive calf stretching with the knee in extended and flexed position on dorsal thigh soft tissue displacement. METHODS: Participants are positioned prone on an isokinetic dynamometer. The device performs three repetitions of moving the ankle passively (5°/s) between plantar flexion and maximum dorsiflexion. With a washout-period of 24 hours, this procedure is performed twice in randomised order, once with the knee extended (0°) and once with the knee flexed (60°). Two high-resolution ultrasound devices will be used to visualize the soft tissue of the calf and dorsal thigh during the manoeuvre. Maximal horizontal displacement of the soft tissue [mm] during ankle movement will be quantified as a surrogate of force transmission, using a frame-by-frame cross-correlation analysis of the obtained US videos. DISCUSSION: Understanding myofascial force transmission under in-vivo conditions is a pre-requisite for the development of exercise interventions specifically targeting the fascial connective tissue. Our study may thus provide health and fitness professional with the anatomical and functional basis for program design. TRIAL REGISTRATION: The study is registered at the German Clinical Trials Register (TRN: DRKS00024420), registered 8 Februar 2021, https://www.drks.de/drks_web/navigate.do?navigationId=trial.HTML&TRIAL_ID=DRKS00024420.