Force transmission in skeletal muscle: from actomyosin to external tendons.

The actual path of force transmission in skeletal muscle from actomyosin interaction to tension at the tendinous insertion site is poorly understood. Within the muscle cell, endo- and exosarcomeric cytoskeletal proteins create series and parallel connections between contractile proteins resulting in a meshwork across which force can be transmitted in practically any direction with respect to the fiber axis. At the surface membrane, connections between the intermediate filament system, dystrophin, and specialized membrane complexes provide the route of force transmission to the extracellular matrix material. Finally, parallel and series connections between muscle fibers allow radial and longitudinal forces to converge on the connective tissue matrix. This complex pathway will certainly be the subject of future studies in muscle biology, biomechanics, and physiology.