What directions do muscles move the legs?
In talking with people about running I have asked them how the different muscles move the limbs. Very few young people know where muscles are located, and they usually have to guess how they move the limbs. Even adults are a little unclear on how muscles work. For example, many people don’t know that the hamstring curls the leg. Some people even thought it extended the leg. With this confusion about how the muscles move the limbs, it is probably even more confusing for them to try to understand how the muscles move the legs to interact with the ground and move the body forward while running.
This lack of understanding is not just an academic deficiency. I think it also limits a person’s ability to learn new movements, and correct bad habits. If they don’t know what muscle produces the desired movement, then they can’t think about the muscle, and focus on contracting it and coordinating it. If they know which muscle should be used, they can think about its contraction and timing through the movement.
I think a major misunderstanding for many people is thinking that the quadriceps are the primary muscles used in running. If a person understands how the quadriceps work, then they can understand that these are not the primary muscles used in running. Three of the four quadriceps attach to the femur and the tibia via the patella. When these muscles contract, they extend the lower leg. This movement extends the leg, but does not extend the body at the hips. Think of straightening the leg while doing a squat without straightening the body at the hips. The legs would push the hips up, but the torso could stay forward. Extending the leg actually moves the foot forward, opposite of the foot’s backward direction required while running. At best, using these three quadriceps while running moves the body upward rather than forward. The remaining one of the four quadriceps, the rectus femoris, attaches the pelvis to the tibia. It is one of the hip flexors, and when this muscle contracts it rotates the femur forward, which is why it is very important in running. This muscle is required in scissoring the legs and bringing the knee forward for the next contraction of the glutes and hamstrings to start the next stride.