July 13, 2016

For muscles to perform external work, they must first overcome inertia due to their internal mass. This is what BPK undergrad Stephanie Ross, under the supervision of James Wakeling, discovered while researching her honors thesis. The research has just been published in Biology Letters.

“It’s similar to starting to run from standing position,” Ross explains.  “Inertia is the resistance of an object to a change in motion because of its mass. In terms of muscles, each muscle is made up of many fibres that produce force, but also have mass and therefore inertia.”

“Most of what we know about how muscles work comes from experiments on fully active isolated fibres and the effects of added mass are ignored” Ross notes. “When every fibre is fully active and producing force to contract the muscle, each fibre primarily activates its own mass. But when only half of the fibres are active, those active fibres have to move their own mass and the “deadweight” of the inactive fibres that are at rest. We hypothesized that the lower the activation and the lower the number of fibres contributing, the harder the active fibres had to work to contract the muscle.”

To determine if this assumption was reasonable, Ross added mass effects to a Hill-type muscle model, a type of computational model that is widely used in the field of biomechanics to predict and understand muscle behaviour.

Ross’s hypothesis proved correct.  “Our findings show that muscle is made up of fibres that each have different levels of activation which directly affects the speed of contraction of the muscle”. She adds, “This suggests that we may need to account for the mass within muscle, particularly when the muscle is large or under natural conditions where the muscle is not fully active.”

Ross’s co-author James Wakeling is pleased that Ross was able to get her research published at an early stage in her career. “This work is very exciting for Stephanie because it combines her love of math and physics with her passion for physiology, giving her many options in terms of future research.”

Ross is now pursuing her MSc degree and studying under SFU’s Injury Prevention and Mobility Lab.