Running involves a series of movements in the ankles, knees, hips and shoulders during every stride. The knee, for example, involves knee extension activated by the quadriceps muscle and knee flexion activated by the hamstrings. With each stride broken into three phases of support, drive and recovery, the joint movement in the knee allows you to maximize your sprinting potential.
The support phase of the sprinting technique is characterized by the foot striking the ground. The quadriceps keep the knee joint nearly fully extended with an eccentric contraction as the foot is in contact with the ground. As the support phase ends, the knee joint starts to flex to absorb shock.
The support phase transitions into the driving phase as the leg extends behind your center of gravity to propel your body forward. The quadriceps, including the rectus femoris, vastus medialis, vastual lateralis and vastus intermedialis, extend the knee joint until the foot leaves the ground. By extending the knee joint, the quadriceps provides additional power during every stride.
The recovery phase of the sprinting motion involves knee flexion to swing the leg forward for another stride. The hamstrings, including the biceps femoris, semimembranosus and semitendinosus, work together to flex the knee while the hip flexors pull the leg forward. As the recovery phase ends, leading into the support phase, the quadriceps begin to extend the knee to prepare for ground contact.
While the basic function and movement of the knee joint remains the same for every phase of sprinting, there are slight personal differences with each running style. While most movements take place in a sagittal plane, personal running styles affect the timing of the knee joint movements along with the range of motion. For example, someone with weak hamstrings may not have a significant knee flexion during the recovery phase.