The trochanteric area, neck, and distal head are supplied by branches of the femoral artery and the proximal head is supplied by branches of the obturator artery travelling within the ligament of the neck of the femur. During development, at about ages 3-4 years, there is a transition from numerous small epiphysial vessels to a limited number of blood vessels, and it is during this transition that the femoral epiphysis is susceptible to vascular compromise. Of course the range of hip flexion is very much influenced by the hamstring muscles, and the position of the knee. The common tendon of iliopsoas crosses the front of the hip joint on its way to the lesser trochanter. Iliopsoas is a hip flexor and may be active during normal standing to help the ligaments prevent hip extension caused by the line of weight passing slightly behind the hip joint centre.
Some muscles actually reverse their actions within the range of hip motion.
Addductor magnus is an extensor in all positions, but adductor longus is a hip flexor in the anatomical position. These muscles act on both the hip and knee. The normal sequence of muscle activity in locomotor tasks such as jumping and sprinting is a proximo-distal one. At the end of knee extension, the gastrocnemius becomes active, the reason as above, together with soleus . During cycling, some of the energy produced by the vasti muscles in knee extension can be transferred by the hamstring muscles to the hip, to produce extension.