What is the main muscle used in sprinting?

Hello Rhett,

So we need to consider this question in a few ways because there are three phases to sprinting - acceleration, full-speed running, and running fast in a state of fatigue.

To be completely honest, there is no "main" muscle used in sprinting, there are so many muscle groups crucial for sprint function. But these are 2 principles that are important so perhaps you might find what I am about to say more useful.

A short limb moves faster than a long limb, but a long limb can generate more force. This is a trade-off, known as conservation of angular momentum and it comes into play in sprinting in two major ways:

Heel Recovery
A sprinter needs to make the leg as short as possible as it swings forward and this is heel recovery. Lifting the heel to the top of the hamstring immediately following the active backward contact stroke shortens the lever of the free leg and creates faster return. Also, when the lower leg is tucked close to the thigh during the recovery phase, strain on the hamstring is reduced.

A low heel recovery creates a long and slow lever that the hamstring has to control to keep the knee from overextending. In other words, because the lever is long, it can produce more force, and the hamstring has to work hard to decelerate the lower leg. Proper heel recovery is more efficient and reduces the chance of injury.

Developmental Considerations
Regarding development, you must understand that children might not have the muscular strength to hold their arms in a disciplined form. The limbs, especially the arms, form long levers that may be creating greater force than the athlete can control. Some athletes regulate this by folding their arms tightly at the elbows to create very short arm levers. Learning to control the arms is important, but it must be addressed through general strength development, as well as patient teaching of proper technique.

There is another important principle called the posture and stretch reflex, but I am going to ignore this for now. You can see that sprinting is a balance, and its a balance of the major muscle groups - biomechanically as I have started to illustrate, and from simple reasons of thinking you start in a crouched position, accelerate low to the ground, and end up at steady pace up tall driving arms and legs up into the air.

Does this answer make sense - I hope it does!