LengthTension

Length-tension describes how the force a muscle can produce depends on its length at the moment of contraction. In skeletal muscle, active tension arises from cross-bridge cycling between actin and myosin filaments, and passive tension comes from elastic components within muscle and surrounding tissue. The overall force a muscle can generate is the sum of these components and varies with the muscle’s length.

The primary mechanism involves the overlap between actin and myosin filaments within the sarcomeres. At an optimal sarcomere length, there is sufficient overlap for maximal cross-bridge formation, producing peak active tension. If the muscle is shorter than this optimum, excessive filament overlap or internal compression can reduce force. If it is longer, there is insufficient overlap, leading to fewer cross-bridges and lower force. Passive elements such as connective tissue and the muscle’s series elastic components contribute increasing resistance as length increases, shaping the total length-tension curve.

In practice, the usable range of lengths depends on muscle architecture, including fiber arrangement and pennation, as well as temperature, fatigue, and contraction type. The curve is typically steeper for muscles with a narrow active range and broader for those designed for a wide range of motion.

Applications of the concept include understanding movement efficiency, informing rehabilitation and athletic training, and guiding clinical assessments of muscle function. While the general pattern is conserved, the exact length-tension profile varies between muscles and individuals.