Running uses nearly every major muscle group in your body, from your calves pushing off the ground to your deep core muscles stabilizing your spine with each stride. While the legs do the obvious work, your hips, trunk, and even your arms play essential roles in keeping you moving efficiently. Understanding which muscles do what can help you train smarter and address weak links before they become injuries.
Glutes: The Powerhouse of Your Stride
Your gluteus maximus, the largest muscle in your body, is the primary driver of forward propulsion. It activates just before your foot strikes the ground and ramps up during the second half of stance phase, accelerating your body forward and upward. It also plays a critical role in stabilizing your trunk so you don’t pitch forward with every step. At moderate speeds (around 12 to 14 km/hr), the gluteus maximus fires at roughly 36% of its maximum capacity in men and 56% in women. Interestingly, at slower jogging paces (8 to 11 km/hr), activation barely changes, hovering around just 4% of maximum. This means your glutes really come alive as you pick up speed.
The gluteus medius, a smaller muscle on the side of your hip, has a completely different job. Every time one foot is on the ground, your pelvis wants to drop on the opposite side. The gluteus medius on your stance leg fires to keep your pelvis level. When this muscle is weak or underactive, that pelvic drop happens, which throws off your knee alignment and can lead to IT band problems, knee pain, and inefficient mechanics. Both the left and right gluteus medius alternate activation throughout the swing and stance phases to keep your hips stable.
Quadriceps and Hamstrings
Your quadriceps, the four muscles on the front of your thigh, work hardest during the landing and early stance phase. As your foot hits the ground, your quads contract eccentrically (lengthening under load) to absorb impact and prevent your knee from buckling. They also help extend your knee during push-off. During swing phase, the quads decelerate knee flexion so your leg doesn’t swing too far back before coming forward again.
The hamstrings, running along the back of your thigh, have one of the most demanding jobs in the entire gait cycle. During late swing phase, as your leg extends forward before foot strike, the hamstrings undergo an active lengthening contraction to decelerate your lower leg. They’re essentially acting as brakes for a rapidly swinging limb. The energy they absorb increases proportionally to the square of your running speed, which is why hamstring strains are so common during sprinting. This late-swing braking action is the moment when hamstrings are most vulnerable to injury.
Hip Flexors and Speed
The iliopsoas, your primary hip flexor, is a deep muscle connecting your lower spine to your thigh bone. During running, it drives your knee forward and upward in the first half of swing phase, pulling your leg through each stride. It also accelerates knee flexion during early swing, helping your foot clear the ground.
What makes the hip flexors particularly interesting is how their role changes with speed. Below about 7 meters per second (roughly a 4:45 mile pace), runners increase speed mainly by lengthening their stride. Above that threshold, the strategy shifts to increasing stride frequency, and the hip flexors become critical. The iliopsoas, gluteus maximus, and hamstrings work together to whip the legs through the air faster, producing nearly double the hip and knee acceleration between 7.0 and 9.0 meters per second compared to slower speeds. Even if you’re not sprinting at elite levels, strong hip flexors contribute to a snappier turnover at any pace.
Calves and Feet
Your calf muscles, the gastrocnemius and soleus, are the last muscles to fire before your foot leaves the ground. They plantarflex your ankle (pointing your toes down) to generate the push-off force that propels you forward. During midstance, they contract concentrically to drive you up and ahead. The soleus, the deeper of the two, handles much of the sustained force during slower running, while the gastrocnemius contributes more explosive power at higher speeds.
On the opposite side of the lower leg, the tibialis anterior and other dorsiflexors pull your toes up toward your shin. They activate during swing phase to clear your foot from the ground and again just before landing to position your foot for the next strike. These smaller muscles work continuously throughout the gait cycle, and when they fatigue, you may notice your feet slapping the ground or catching on uneven surfaces.
Core and Trunk Muscles
Running places significant rotational forces on your torso. Every time your right leg swings forward, your trunk wants to rotate to the right, and vice versa. A network of core muscles works constantly to control this rotation and transfer force between your upper and lower body.
The deep stabilizers do the fine-tuning work. The lumbar multifidus, a series of small muscles connecting one vertebra to the next, controls the precise positioning of your spinal segments. The transversus abdominis and the lower fibers of the internal oblique attach to the lumbar spine through connective tissue and act as a natural corset, stiffening your trunk against the repetitive impact of each footfall.
The larger, more superficial muscles handle torque and gross stability. Your rectus abdominis (the “six-pack” muscle), external obliques, and even the latissimus dorsi in your back all contribute to controlling trunk rotation and maintaining an upright posture. The gluteus maximus also plays a role here, connecting through the thoracolumbar fascia to help stabilize the spine from below. Weakness in any layer of this system forces other muscles to compensate, often leading to low back pain or hip issues in runners.
Arms and Shoulders
Arm swing might look like a passive byproduct of running, but it serves a specific mechanical purpose: counterbalancing the rotational momentum generated by your swinging legs. Without arm swing, your torso would rotate much more with each stride. Research published in the Journal of Experimental Biology found that when runners held their arms still, both shoulder and pelvic rotation increased significantly as the body tried to compensate.
That compensation is expensive. Your torso accounts for 40 to 50% of your total body mass, while both arms together make up only about 10%. Swinging 10% of your mass to counterbalance leg momentum is far more energy-efficient than rotating 40 to 50% of your mass. The deltoids, rotator cuff muscles, and upper back muscles drive and control arm swing, while the biceps maintain a tonic contraction to keep your elbows bent at the roughly 90-degree angle most runners naturally adopt. It’s a small energy cost that pays for itself many times over.
How Muscle Demands Change With Speed
At a slow jog, the calves and quads do most of the work, with the glutes barely engaged. As you increase to a moderate pace, the gluteus maximus ramps up substantially and the hamstrings take on more eccentric load. At faster speeds approaching a sprint, the hip flexors and hamstrings become the dominant players, generating the rapid limb acceleration needed for high stride frequencies. The core muscles also work harder at faster paces because rotational forces increase with speed.
This progression explains why different types of runners get injured in different ways. Distance runners commonly develop calf, shin, and knee issues tied to repetitive loading at moderate muscle activation levels. Sprinters are far more likely to suffer hamstring strains because of the enormous eccentric forces during late swing phase. Targeting your training to the muscles most active at your typical pace is one of the most practical things you can do to reduce injury risk and run more efficiently.