English

Noun

tendons

1. Plural of tendon

French

Verb

1. Form of First-person plural present indicative, tendre
2. Form of First-person plural imperative, tendre

A tendon (or sinew) is a tough band of fibrous connective tissue that usually connects muscle to bone and is capable of withstanding tension. Tendons are similar to ligaments except that ligaments join one bone to another. Tendons and muscles work together and can only exert a pulling force.

Anatomy

The origin of a tendon is where it joins to a muscle. Collagen fibers from within the muscle organ are continuous with those of the tendon. A tendon inserts into bone at an enthesis where the collagen fibers are mineralized and integrated into bone tissue. While they exert no pulling force of their own, tendons transfer the contractions of muscles and can exert an elastic force if forcibly stretched.

Structure

Normal healthy tendons are composed of parallel arrays of collagen fibers closely packed together. The fibers are mostly collagen type I, however there is also collagen type III and V present. These collagens are held together with other proteins, particularly the proteoglycan, decorin and, in compressed regions of tendon, aggrecan. The tenocytes produce the collagen molecules which aggregate end-to-end and side-to-side to produce collagen fibrils. Fibril bundles are organized to form fibers with the elongated tenocytes closely packed between them. Collagen fibers coalesce into macroaggregates. Groups of macroaggregates are bounded by connective tissue endotendon and are termed fascicles. Groups of fascicles are bounded by the epitendon and peritendon to form the tendon organ.

Blood vessels may be visualized within the endotendon running parallel to collagen fibers, with occasional branching transverse anastomoses.

The internal tendon bulk is thought to contain no nerve fibers, but the epi- and peritendon contain nerve endings, while Golgi tendon organs are present at the junction between tendon and muscle.

Tendon length varies in all major groups and from person to person. Tendon length is practically the discerning factor where muscle size and potential muscle size is concerned. For example, should all other relevant biological factors be equal, a man with a shorter tendons and a longer biceps muscle will have greater potential for muscle mass than a man with a longer tendon and a shorter muscle. Successful bodybuilders will generally have shorter tendons. Conversely, in sports requiring athletes to excel in actions such as running or jumping, it is beneficial to have longer than average Achilles tendon and a shorter calf muscle.

Tendon length is determined by genetic predisposition, and has not been shown to either increase or decrease in response to environment, unlike muscles which can be shortened by trauma, use imbalances and a lack of recovery and stretching.

Pathology

Tendonitis refers to inflammation of a tendon.

Tendinosis refers to non-inflammatory injury to the tendon at the cellular level.

Other information

The Achilles tendon is a particularly large tendon connecting the heel to the muscles of the calf. It is so named because the mythic hero Achilles was said to have been killed due to an injury to this area.

Sinew was also widely used throughout pre-industrial eras as a tough, durable fiber. Some specific uses include using sinew as thread for sewing, attaching feathers to arrows (see fletch), lashing tool blades to shafts, etc. It also recommended in survival guides as a material from which strong cordage can be made for items like traps or living structures. Tendon must be treated in specific ways to function usefully for these purposes. Inuit and other circumpolar people utilized sinew as the only cordage for all domestic purposes due to the lack of other suitable fiber sources in their ecological habitats.

The elastic properties of particular sinews were also used in composite recurved bows favoured by the steppe nomads of Eurasia. The first stone throwing artillery also used the elastic properties of sinew.

Tendon (particularly beef tendon) is used as a food in some Asian cuisines (often served at Yum Cha or Dim Sum restaurants). One popular dish is Suan Bao Niu Jin, where the tendon is marinated in garlic.

See also

• Aponeurosis
• Chordae tendineae
• Cartilage
• Tendon sheath

References