Muscle tissue is made of molecular engines called sarcomeres, which contract and expend when the muscle is flexed. In sarcomeres the business of contracting is carried out by molecular motors called myosins as they pull themselves along filaments of a protein called actin. When you flex your arm, it is these myosin molecular motors that are doing the work.
One curious phenomenon that can sometimes be observed in muscles is a wavelike oscillation of the tissue. What causes this infamous “rippling” of muscles has been somewhat of a mystery but today Stefan Gunther and Karsten Kruse from Saarland University in Germany throw some light on the matter.
They’ve modeled the rate at which molecular motors detach themselves from the actin filaments as the load they are under changes. It turns out that oscilllations occur naturally under certain loads, as the molecular motors attach and re-attach.
So when the next bodice ripper you read mentions rippling muscles, you’ll know exactly what this means.
Ref: arxiv.org/abs/0901.4517: Spontaneous Waves in Muscle Fibres