Tendons, also called sinews, are connective tissues that connect the muscles to the bone which send the mechanical force of muscle contraction to the bones. Muscle fibers connect the tendons to both the bone and the muscle. Composed mainly by spindle-shaped cells called fibrocytes and tough collagenous fibers, tendons have great tensile strength that can accommodate the stress exerted by the muscular contractions.
Tendons enable the body to move and be flexible. Walking, running, jumping, lifting, dancing, and other physical activities are enabled by the tendons. The length of the tendon is dictated by genetics and determines the muscle size. It is a great advantage for runners and jumpers to have longer than average tendons at the back of the heel and shorter calf muscles.
It is common among athletes, laborers and active people who overwork or overstrain their tendons to have problematic tendons usually in the knee, ankle, wrist, biceps, shoulders, calf and at the back of the heel. Small tears caused by the repetitive strenuous action lead to tendonitis. Healing takes time and would require complete rest. Other times, surgery is performed to repair damaged tendons.