3D whole muscle shape changes–exploring a novel approach

Muscle shape changes occur when animals move and are inevitable when generating muscle force, yet we know little about its functional role in force production. Here we explore a novel approach for experimentally measuring 3D whole muscle shape changes using X-ray imaging. Fresh cadaveric lower limbs of the domestic chicken (Gallus gallus domesticus) were used. After surgically opening the skin and removing the connective tissue surrounding the muscle, 35 opaque beads (ϕ = 0.35mm) were fixated around the lateral gastrocnemius with a cyanoacrylate. High-speed stereo (3D) X-ray videos (750 Hz) were recorded while the muscle was stretched over two cycles by applying a force on the tendon. Two of the 35 markers were removed from analyses. Of the remaining 33 muscle markers, the displacement during muscle stretch ranged from 6.15 to 8.86mm and 6.11 to 9.05mm for cycle 1 and 2 respectively.
Comparing the distance between each marker and a bony reference marker at the start and end of each cycle we found very small changes (mean: 0.07 ± 0.12mm and 0.05 ± 0.05mm for the two), indicating no shifts in bead placement along the muscle surface. These preliminary results suggest that the proposed
approach can be used to track 3D whole muscle shape changes dynamically, at least during passive muscle stretching. We aim to extract whole muscle shape changes and validate this technique during in situ muscle contraction.