“Avatar”, a Modified Ex vivo Work Loop Experiments Using In vivo Strain and Activation

The goal of my laboratory is to understand in vivo muscle function by developing new experimental paradigms for ex vivo experiments and models that really relate to in vivo muscle function. The kind of experiments and models that we’ve been using over the past 20 years, it’s become more and more obvious that they really don’t relate to in vivo muscle function. Currently, there is a knowledge gap between top-down approaches that measure muscle function in vivo during dynamic movements of humans and animals, and bottom-up approaches that use controlled ex vivo and/or in situ experiments that measure muscle mechanics under isometric and/or isotonic conditions.

We are trying to design physiologically relevant ex vivo and in situ experiments that inform in vivo muscle mechanics. The most commonly used technique in our field is the sinusoidal work loop technique developed by Bob Josephson in the mid 1980s. This technique uses sinusoidal or sometimes satu strain trajectories at in vivo frequencies with in vivo stimulation patterns to emulate in vivo muscle function.

However, our Avatar technique demonstrates that deviations from purely sinusoidal strain trajectories resulting from foot contact during terrestrial locomotion are important determinants of muscle force and work.