Most skeletal muscle attaches to bone in order to produce movement. However, some skeletal muscle attaches directly to other muscles, fascia, or tissues such as the skin.

Tendons

A tendon is a cord-like, fibrous connective tissue that connects muscle to bone and is capable of withstanding tension. At either end of the tendon, its fibers intertwine with the fascia of a muscle or the periosteum (a dense fibrous covering of a bone), allowing force to be dissipated across the bone or muscle.

Tendons mainly consists of closely-packed collagen fibers running parallel to the force generated by the muscle to which they are attached. Intertwined with the collagen fibers are elastin molecules, which improve the tendons' elasticity, and various proteoglycans, proteins to which many carbohydrate molecules are attached. These proteins play a key role in maintaining the organization of the tendon, especially during compression and extension.

Tendons were once thought to play only a passive connective role. However, research into their elastic properties has demonstrated that they can also act as springs. The elasticity of tendons allows them to passively store energy for later release. The most widely-researched example is the Achilles tendon which stores and releases elastic energy during walking, improving efficiency and reducing muscle load.

Achilles Tendon

The Achilles tendon provides stability and limits the range of motion at the ankle joint. It is the thickest and strongest tendon in the body. Tendons are a common tissue that connect muscle to bone.

Aponeuroses

Not all muscle attaches via tendons. Aponeuroses are large, sheet-like layers of connective tissue with a similar composition to tendons. Aponeuroses can also attach to bone, as in the scalp aponeuroses, and to the fascia of other muscles or tissues, such as the anterior abdominal aponeuroses. Their large form and shape provides structure and distributes tension across a wider area or large number of muscle groups.

Other Attachments

Muscles can also attach directly to other tissues, which is most evident in the face. The skeletal muscles involved in controlling expression attach directly onto the fascia of the skin.