Foot is in contact with the ground and supports the body against gravity.
The center of gravity for a runner is usually the lower abs between the hips.
3 Phases of Leg Stride
This is when leg extension occurs at the knee joints and hips. This part of movement is when the toe is in contact with the ground and the leg trails behind the body. Most of the power comes from the quadriceps at this point.
The hip flexes while the toe is in the air moving the knee forward. This is where the hip flexes the most. During this extension the hamstring and gluteal muscles are used.
Upper Body Movement
Upper body movement is just as important as the lower body. It is essential for maintaining balance and forward momentum.
The upper body compensates for the lower body by a rotational balance. An arm movement forward balances a leg movement backward. Shoulders play a key role in this movement.
Much of a runners energy is put towards compensating movements. The ability to have free movement and correct techniques will eliminate wasteful energy.