This review considers the physical mechanism of mechanochemical processes in living organisms, based on the determining roles of excited hydrogen bonds in biological molecules in stimulation of muscle contraction.The review comprises two parts. The first part presents known facts on biomolecules and energy transmission mechanisms. The second part is a detailed exposition of authors' results on the physical mechanisms of muscle contraction due to excited state - normal state transitions and inverse transitions. The problems are interdisciplinary involving aspects of physics, biology, biochemistry and natural sciences.