Gastrocnemius fascicle length changes with two-joint passive movements

Area of Science:

• Biomechanics
• Human Physiology
• Musculoskeletal System

Background:

• Understanding muscle fascicle length changes during passive movements is crucial for comprehending muscle function.
• Previous kinematic models exist but require experimental validation during dynamic joint actions.

Purpose of the Study:

• To experimentally compare gastrocnemius fascicle length changes during passive two-joint movements.
• To validate a previously derived kinematic model against experimental ultrasound data.
• To quantify fascicle length changes in the medial and lateral gastrocnemius during combined ankle and knee motion.

Main Methods:

• Ultrasound imaging was used to acquire gastrocnemius fascicle lengths.
• Passive ankle and knee movements were performed, manipulating the ratio of motion between joints.
• Measurements were taken at 10-degree increments of knee flexion.

Main Results:

• The previously derived two-joint kinematic model did not adequately predict fascicle length changes under the tested movement conditions.
• Experimental data revealed specific rates of fascicle length change per degree of joint motion: Medial gastrocnemius: 0.42 mm/degree (ankle), 0.14 mm/degree (knee).
• Lateral gastrocnemius: 0.96 mm/degree (ankle), 0.22 mm/degree (knee).

Conclusions:

• The current two-joint kinematic model is insufficient for accurately predicting gastrocnemius fascicle length changes during passive movements.
• The study provides novel experimental data quantifying fascicle length changes in response to isolated and combined ankle and knee motion.
• Further refinement of biomechanical models is needed to incorporate the complex fascicle dynamics observed in the gastrocnemius.