The functioning of the human leg is the result of cooperation between the muscles and bones located there. Many muscles involved in leg function are quite large and use powerful contractions to propel and support the body. In addition muscles combined with the leg's bone structure are responsible for adjusting to minute changes, thus ensuring the body remains balanced in standing, walking or running modes.
Different muscle groups are responsible for the action of the major joints in the leg. For example the muscles of the buttocks, hips and pelvis are essential for the proper performance of the hip joint, which is a ball-and-socket joint. Alternatively, the quadriceps and other muscles of the thigh are meant to execute lifts and extensions above the knee.
The knee itself is a joint that affords the leg an immense amount of flexibility and is the site where the two major leg bones, the femur and the tibia, meet. The knee also provides a nexus for various tendons and ligaments that facilitate leg function. In the lower leg, the Achilles tendon is vital. It connects the three muscles of the lower leg to the all-important heel bone. Its crucial position explains why injuries to the Achilles tendon, especially among athletes, can be so damaging to their performance. Such injuries often require surgery and six to nine months of rehabilitation.