Meeting Abstract
Muscles produce an amazing range of animal movements, and much of their function as biological motors depends on how much—and how fast—they change in length. Hence, measurements of in vivo muscle length changes are essential for understanding the mechanisms of muscle-powered motion. We describe the methods and validation of fluoromicrometry, a technique for measuring muscle length using biplanar X-ray videos. Small (0.5-0.8 mm), radio-opaque markers are surgically implanted into a muscle, and the freely-moving animal is recorded with biplanar fluoroscopy. The 3D position of each marker is calculated from the X-ray videos (using free XROMM software), and the change in distance between adjacent markers used to measure muscle length throughout the behavior. We have measured the precision of fluoromicrometry to be 0.09 mm, and confirmed that it is accurate, with no significant bias in the resulting length measurements. Fluoromicrometry has been used to study several animals and behaviors including axial muscles in feeding fish, the plantaris muscle in jumping frogs, and hind-limb muscles in walking rats. Fluoromicrometry allows for wireless data collection, a large number of intramuscular markers, the potential for long-term implantation, and 3D position and motion data for each marker. It can be collected synchronously with X-Ray based skeletal kinematics (XROMM) to examine the interaction of muscle and bone motion, and in particular the contribution of muscle and tendon to the overall length of muscle-tendon units. While it is limited by the small imaging volume and accessibility of biplanar X-ray filming, fluoromicrometry provides an exciting new tool for investigating musculoskeletal biomechanics.
