Distinct displacement of the superficial and deep fascial layers of the iliotibial band during a weight shift task in runners: An exploratory study.

Motion of the fascial layers of the iliotibial band (ITB), as a reinforcement of the deep fascia lata, is likely to be relevant for its function and mechanical behaviour. This exploratory study aimed to evaluate the ITB fascial layers displacement during a weight shift task. Thirteen pain-free runners performed a 6-second standing weight shift task. B-mode ultrasound imaging using an automated fascicle tracking algorithm was used to measure proximal and distal displacement of superficial and deep ITB layers at the middle region. To study the potential contributors to individual variation of fascial motion, we recorded the activity of five hip/thigh muscles with electromyography (EMG), thigh/pelvis/trunk position with accelerometers, and centre of pressure with a force plate. Linear regressions estimated the relationship between displacement of fascial layers and hip/trunk angles. Independent t-tests or Fisher's exact tests compared EMG and movement-related parameters between participants who demonstrated motion of the fascia in the proximal and distal directions. Thickness of the ITB and the loose connective tissue between its layers were calculated. Proximal displacement was observed in six (-4.1 ± 1.9 mm [superficial]) and two (-6.2 ± 2.0 mm [deep]) participants. Distal displacement was observed for seven participants for each layer (3.1 ± 1.1 mm [superficial]; 3.6 ± 1.3 mm [deep]). Four participants did not show displacement of the deep layer. Trunk lateral flexion and gluteus medius muscle activity were determinants of proximal motion of the superficial layer. Loose connective tissue was thinner in participants without displacement of the deep layer. Displacement of the ITB fascial layers varies between individuals. Variation related to differences in joint movements and muscle activity. This study highlights the complex interaction between fascia and movement.