When you look at someone running, it’s obvious that their legs and arms are pumping hard, but is there more to it than that? There definitely is. If you have ever asked the question, “What muscles does running work?” Then this article is for you. We are going to break it down by phase, and teach you about some of the fascinating muscles that allow us to run properly.

Phases of Running

When looking into what muscles are working at what time while running, it is important to have a brief understanding of the different phases of the running cycle. While several muscles are working during this exercise, the majority of the motion takes place in the lower extremity. We’ll start by quickly looking at how the leg moves by referencing the picture below.

Two main phases of running gait, stance and swing. One full cycle illustrated by this runner’s right leg. (Credit: Adobe Stock w/edits in red by author)

Stance Phase

Stance phase is the period when the foot is in contact with the ground. It can be further divided into initial contact, when the foot first makes contact with the ground; midstance, when the body's weight is directly over the supporting foot; and terminal stance, when the body continues to move forward as the foot lifts off the ground.

The stance phase is crucial for providing stability and support during the running motion. It is the point at which you absorb the most force upon making contact with the ground, and is subsequently where many people tend to develop injuries. The eccentric forces on various tissues throughout the leg can be tremendous in this phase depending on your form.

Various factors such as the alignment of the lower limbs, muscle strength, and flexibility significantly influence the distribution of forces across the body. Optimal alignment and muscle activity during the stance phase are vital for minimizing excessive stress on the joints and soft tissues. Otherwise common injuries include shin splints, plantar fasciitis, and stress fractures.

Swing Phase

Swing phase occurs when the foot is not in contact with the ground. It involves the leg swinging forward in preparation for the next footstrike. The swing phase is essential for generating momentum and propelling the body forward during running. This is in stark contrast to the stance phase, where the focus is dedicated primarily to stability of the leg instead of movement.

Forces during this phase of the running cycle are more concentric (shortening) than in the stance phase. The initial phases of stance involve absorbing force from the landing, causing several muscles to work eccentrically (by lengthening under load). As we leave the ground and move our legs through the air during swing, several muscles are contracting to create that movement.

While the swing phase is associated with less impact than the stance phase, certain types of injuries are still more likely to occur at this point in the stride. Hamstring pulls, hip flexor pulls, calf injuries, groin strain, and even labral tears are all possible. The strength and resilience of your muscle tissue will be a large factor in the likelihood of whether such injuries will occur.

(Credit: Adobe Stock)

Muscles Used In Running

Let’s now take a look at each phase to determine what muscles are actually working while we are running. We’ll then take a brief look at the important role that the core musculature has in dissipating force as it enters into the system, and also how it allows us to effectively transmit force out through the legs.

Muscles Used In Stance Phase

The quadriceps help you to land effectively with each step. Their job is to extend (straighten) the knee, so when the knee goes into a slight bend upon landing, that is the quadriceps stretching under load (remember, eccentrically) to help absorb the shock of the impact. When this is ineffective, susceptibility to things like runner’s knee is more likely.

Calf muscles (gastrocnemius and soleus) have the same operating mechanism, just at the ankle joint instead of the knee. Both these muscles are plantar flexors (they point your toes), and when you land, the reverse motion takes place. If you land with a mid-forefoot strike, you’re basically performing the descent of a calf raise as your foot flattens and the calf muscles are stretched.

Finally, your hip muscles are working overtime in stance phase to stabilize the pelvis and effectively dissipate force from the ground, up through the lower extremity, and throughout the rest of the body. Gluteus medius and minimus are working particularly hard on the leg in stance to help prevent the pelvis from dropping down on the opposite side.

(Credit: Adobe Stock)

Muscles Used In Swing Phase

Three muscles on the back of your thigh (semimembranosus, semitendinosus, biceps femoris) form the hamstrings group, which have important functions while running. During swing phase, they bend the knee and extend the hip to help bring the leg behind you. They also help your leg slow down as it swings through for the next step on your run.

Iliopsoas, which is actually two muscles working together with a similar function (iliacus and psoas major), are both hip flexors. This means they flex the hip joint by bringing the leg in front of you and moving the knee towards the chest. These are both important functions when the leg reaches back as far as it can and then begins to move forward in preparation for the next step.

Another important muscle active in swing phase is the tibialis anterior. This muscle makes up the bulk of the tissue on the front of your shin beside your shin bone. Its function is dorsiflexion, which means pulling the toes up towards the shin. This happens as the leg swings through to avoid the foot from hitting the ground. This muscle is also an important shock absorber.

Core Muscles & Running

The core musculature is highly functional throughout the process of running. When we say the core, we are referring to primarily the muscles in and around your torso, i.e. abdominals, lower back muscles, diaphragm, and pelvic floor. The purpose of the core while running is to provide stability and effectively dissipate and transmit force throughout the body and into the ground.

Transversus abdominis and internal oblique, both deep abdominal muscles, form what is called the inner unit. The inner unit is responsible for spinal and pelvic stabilization, both critical while running. If these key structures were unstable, they would wear out quickly, and do in many runners who do not have adequate strength in these tissues. Low back pain is a common result.

(Credit: Adobe Stock)

The outer unit is formed by bigger, more superficial back muscles and abdominal muscles, including external oblique and rectus abdominis, the latter of which is better known as your “six pack”. These muscles provide more gross stabilization and movement capabilities, and also help transfer force absorbed by the legs up through the rest of the body.

Several sling systems are intelligently linked together to help make movement more efficient for the runner, but are unfortunately outside the scope of this article to explain. What is important to know is that running is a total body sport, and that preventing injury to the runner involves a comprehensive program that trains the body in ways that are functional.

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 Written by Eric Lister – Certified Personal Trainer & Corrective Exercise Specialist