Running is a total-body activity. Virtually every muscle in your body is involved in the process of driving your body forward and then getting ready to move into the right position to do it over and over again. That being said, running is commonly thought of as a lower body-dominant activity, and it is possible to identify a number of major leg muscles responsible for developing running speed.
Calf Muscles
There are two main calf muscles: the gastrocnemius and the soleus. The gastrocnemius is the larger of the two and is responsible for extending your ankle and also weakly flexes your knee. The smaller soleus muscle lies below the gastrocnemius and its sole function is to extend your ankle. These two powerful muscles work together to push you forward off your toes. The faster you run, the harder these muscles tend to work, so strengthening them makes sense if you want to run faster.
Posterior Thigh Muscles
The muscles on the back of your thigh are called your hamstrings and are made up from the semimembranosus, semitendinosus and biceps femoris muscles. These muscles work together to bend your knees and extend your hips backward. Pulled or injured hamstrings are common in sprinting, which illustrates how hard these muscles work when you run fast. Leg curls and stiff-legged deadlifts are two common and effective exercises for strengthening the hamstrings.
Posterior Hip Muscle
The main muscle on the back of your hip is called the gluteus maximus, or glutes for short. Essentially your butt, this large and powerful muscle drives your hip back and into extension and works in conjunction with the hamstrings. Sprinters often have very well-developed glutes, which is testament to how important this muscle is in fast running.
Anterior Thigh Muscles
The muscles on the front of your thigh are called your quadriceps and consist of four muscles: rectus femoris, vastus lateralis, vastus intermedius and vastus medialis. These muscles work together to extend your knee; the rectus femoris is also responsible, along with the hip flexors, for swinging your leg forward and into your next stride. The quadriceps do not contribute much in the way of forward thrust when running, but they are essential for stopping your legs from collapsing as you move from one stride to the next.
Medial and Lateral Thigh Muscles
The muscles on the inside and outside of your thighs are the adductors and abductors, respectively. These muscles provide little in the way of thrust but are responsible for keeping your knees and hips properly aligned and stable. The faster you run, the more unstable your hips and knees are likely to become, so strong adductors and abductors can help improve running efficiency which indirectly affects your running speed. Running on uneven ground will significantly increase the amount of work these muscles have to do.
