Tendon the Achilles tendon stretches as the ankle joint dorsiflexes. During the last portion of the stride, as the foot plantar-flexes (pointing the toes down), the stored elastic energy is released. Furthermore, because the tendon stretches, the muscle is able to function with less or even no change in length, allowing the muscle to generate greater force. The mechanical properties of the tendon are dependent on the collagen fiber diameter and orientation. The collagen fibrils are parallel to each other and closely packed, but show a wave-like appearance due to planar undulations, or crimps, on a scale of several micrometers. In
Human vestigiality dorsi to the long head of the triceps brachii. It is notable due to its well developed character in other apes and monkeys, where it is an important climbing muscle, namely the dorsoepitrochlearis brachii. This muscle is found in ≈5% of humans. The plantaris muscle is composed of a thin muscle belly and a long thin tendon. The muscle belly is approximately long, and is absent in 7–10% of the human population. It has some weak functionality in moving the knee and ankle but is generally considered redundant and is often used as a source of tendon for grafts. The