Muscle–Tendon Unit

A muscle–tendon unit, or MTU, is the functional mechanical system formed by skeletal muscle and the tendinous tissues connected to it. It includes the force-generating muscle fibers together with force-transmitting structures such as tendons and, where present, aponeuroses. Considering these tissues as one unit helps explain how muscular force and mechanical energy are transferred during movement .^1,2

The muscle and tendon components have different mechanical roles. Active muscle fibers can generate force and perform mechanical work, whereas tendons and aponeuroses transmit force and can stretch under load. Because tendinous tissues have elastic properties, some mechanical energy can be stored as they lengthen and subsequently returned as they recoil .^1,2

The behavior of the whole muscle–tendon unit does not necessarily match the behavior of its muscle fascicles. For example, a tendon can lengthen while active muscle fascicles shorten, allowing the overall length of the unit to change relatively little. This interaction can influence the speed and length at which muscle fascicles operate and can contribute to energy storage, power production, or energy absorption during movements such as walking, running, jumping, and landing .^1,2

The muscle–tendon unit should not be confused with the musculotendinous junction, which is specifically the interface where muscle fibers connect with tendon-associated connective tissue. The muscle–tendon unit is the broader functional system comprising the muscle and its connected tendinous structures .^1,2