The hamstring muscles, or, knee flexor muscles are a group of three muscles located in the posterior thigh region on both sides of the body. These muscles are loaded with fast twitch fibers and are a must for an athlete to exercise if they want to increase running speed. Their names are: 1) Semitendonosus, 2) Biceps Femoris and 3) Semimembranosus and are shown below in Figure 1.
Figure 1. The Hamstring Muscle, or, Knee Flexors.
Innervation, or, Nerve Supply of the Hamstring Muscles
The nerve supply to the hamstring muscles is supplied by the great sciatic nerve. It is the largest nerve cord in the body and is as thick around as your thumb. It is formed by the fourth and fifth lumbar nerves and the first three sacral nerves. Injury to this nerve is quite painful and is more often than not caused by a tight piriformis muscle which is an external hip rotator to be talked about in another post.
Function, or, Action
The hamstring muscles have two functions: 1) flex the leg behind the thigh as shown in by the athletes right leg in Figure 2, below and 2) extend the thigh behind the hip as shown by the athletes left leg in Figure 2.
Figure 2. Muscles involved: R-Semitendonosus, R-Biceps Femoris and R-Semimembranosus as shown.
As you can see, the hamstring muscles are an important muscle group for anyone looking to increase running speed. These muscles, however, are also one of the most likely to get injured while running due to strength imbalances in the body.
Antagonist Muscles to the Hamstrings
Muscles that work opposite one another are known as antagonist muscles. Since the hamstrings have two functions, they will have two antagonists. The first one works opposite knee flexion and that is the quadriceps. The other works opposite of hip extension and that is the hip flexors. Both of the muscle groups will be talked about in other posts.
