Muscle power-stroke as a collective mechanical phenomenon
Matthieu Caruel (Inria and École Polytechnique)
The mechanism of muscle contraction, residing in nano-scale interaction between actin and myosin filaments, was intensely studied by using fast loading protocols. These experiments revealed the important mechanical role of the internal conformational change inside protruding myosin heads known as the power-stroke. It was realized that fast force recovery after abrupt loading, taking place at 1 ms time scale, is a purely mechanical phenomenon linked exclusively to the power-stroke and not limited by metabolic fuel delivery.
In this presentation, we explore previously unnoticed difference in fast force recovery taking place in hard and soft loading devices and propose a purely mechanical model that explains the origin of this unusual behavior. We link the inequivalence of soft and hard loading ensembles to the presence of long range interactions between the individual actin-myosin cross-links known as cross-bridges. Our fit of experimental data suggests that ‘muscle material’ is finely tuned to perform close to a critical point which explains large fluctuations observed at stall forces. The proposed mean field model clarifies the collective nature of the power-stroke and reveal new properties of the celebrated Huxley and Simmons 1971 model.