Tendon the endotendon running parallel to collagen fibres, with occasional branching transverse anastomoses. The internal tendon bulk is thought to contain no nerve fibres, but the epitenon and paratenon 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, in practice, the deciding factor regarding actual and potential muscle size. For example, all other relevant biological factors being equal, a man with a shorter tendons and a longer biceps muscle will have greater potential for muscle mass than a man
Achilles tendon rupture can also contribute to injury. Fluoroquinolone antibiotics, famously ciprofloxacin, are known to increase the risk of tendon rupture, particularly Achilles. People who commonly fall victim to Achilles rupture or tear include recreational athletes, people of old age, individuals with previous Achilles tendon tears or ruptures, previous tendon injections or quinolone use, extreme changes in training intensity or activity level, and participation in a new activity. Most cases of Achilles tendon rupture are traumatic sports injuries. The average age of patients is 29–40 years with a male-to-female ratio of nearly 20:1. Direct steroid injections into the tendon have also been linked