Walking on an incline treadmill works your glutes, hamstrings, calves, and quadriceps significantly harder than flat walking. Even a modest grade of about 3 degrees (roughly 5%) is enough to measurably increase activation in most of these muscle groups, and the demand keeps climbing as the slope gets steeper. Your core and hip flexors also contribute more than you might expect, making incline walking a surprisingly complete lower-body workout.
Glutes and Hamstrings
The gluteus maximus and hamstrings see some of the largest jumps in activity when you add incline. EMG studies show that both muscles increase in magnitude and duration of activation at inclines of 15% and above compared to level walking, but the shift begins at grades steeper than about 3 degrees (around 5%). At every step on a slope, your glutes and hamstrings must work harder to extend your hip and drive your body upward against gravity, essentially turning each stride into a small uphill push.
This is why incline treadmill walking is so popular for glute training. On flat ground, your glutes do relatively little work because you’re moving forward, not upward. Add a steep incline and the demand on the posterior chain rises sharply. The biceps femoris, the outer hamstring muscle, shows especially strong increases in activation, making incline walking a practical option for people who want to load their hamstrings without the joint stress of heavy squatting or deadlifting.
Quadriceps
Your quadriceps, the four muscles on the front of your thigh, fire at heel contact to control your knee and absorb your body weight on each step. On an incline, the vastus medialis and vastus lateralis (the inner and outer quad muscles) increase their activity at grades steeper than 3 degrees, while the rectus femoris, which also crosses the hip joint, kicks in more noticeably above 6 degrees.
Interestingly, the quadriceps also work harder during downhill walking, but for a different reason: they act as brakes to control your descent. On an uphill grade, the quads are generating force to push you up. So incline treadmill walking trains these muscles in a concentric, power-producing way rather than just an eccentric, shock-absorbing way.
Calves: Soleus and Gastrocnemius
The calf muscles do a surprising amount of heavy lifting on an incline. The soleus and gastrocnemius are the two largest muscles responsible for pushing off at the ankle, and both show significant activation increases as the grade rises. Research in the Journal of Biomechanics found that the ankle’s push-off force increases from about 1.62 Nm/kg on flat ground to 2.16 Nm/kg at a 10% incline, a roughly 33% jump.
The soleus deserves special mention. It has one of the largest cross-sectional areas of any muscle in the lower leg, and its increased workload on an incline is a major reason why incline walking burns more calories than flat walking at the same speed. If your calves feel noticeably more fatigued after an incline session, it’s because they’re providing substantially more propulsive force with every step.
Tibialis Anterior (Shins)
Here’s a counterintuitive finding: the tibialis anterior, the muscle running along your shin, actually decreases in activation as incline increases. On flat ground this muscle works hard to lift your toes and control your foot as it lands. On a slope, the angle of the surface means your foot doesn’t need to dorsiflex (pull upward) as much, so the shin muscle gets less of a workout. If you’re looking to strengthen your shins specifically, flat or slightly downhill walking is more effective than steep inclines.
Hip Flexors
Your hip flexors, the deep muscles connecting your spine and pelvis to your thigh bone, work harder on an incline to swing each leg forward and clear the rising surface. Biomechanical modeling shows that the iliopsoas (your primary hip flexor) generates meaningful power to the leg during the late stance phase of uphill walking. At a 24% grade, hip range of motion increases by about 20% compared to flat ground, which means your hip flexors are stretching further and contracting through a longer range with every stride.
This matters for anyone who sits at a desk most of the day. Incline walking takes the hip flexors through a fuller range of motion than flat walking, which can help counteract the shortening and stiffness that comes from prolonged sitting.
Core and Spinal Muscles
Walking uphill shifts your center of gravity forward, and your body must constantly stabilize against that change. The erector spinae muscles running along your spine work to keep your torso upright during forward propulsion. Your obliques and deep abdominal muscles co-contract to prevent excessive rotation and side-to-side sway. This isn’t the kind of core work that will build visible abs, but it strengthens the stabilizers that protect your lower back during everyday movement.
The postural demand increases with steeper grades because your trunk has to resist a greater forward lean. People with lower back pain sometimes notice that walking on moderate inclines feels more challenging for their back muscles, which is consistent with research showing higher erector spinae activation during forward movement in people with spinal instability.
When Muscle Activation Shifts
Not all inclines are created equal, and the research points to a clear threshold. A study in Gait & Posture found that compared to flat walking, the glutes, hamstrings, inner quads, and soleus all increased significantly at grades steeper than 3 degrees (about a 5% setting on most treadmills). The medial gastrocnemius, your inner calf muscle, increased at every uphill grade tested. The rectus femoris needed a steeper slope, kicking in above 6 degrees (roughly 10%).
So if you’re walking at 1% or 2% on the treadmill, you’re barely changing muscle recruitment from flat walking. The meaningful shift starts around 5%, and it intensifies progressively from there. There’s no single “best” incline, just a dose-response curve: steeper grades recruit more muscle, burn more energy, and demand more from your cardiovascular system.
Joint Impact at Higher Inclines
One benefit that surprises many people is that incline walking can actually reduce stress on certain parts of the knee. The peak internal knee abduction moment, a measure of loading on the inner knee compartment, drops significantly as incline increases. At 0% grade it averages about 0.54 Nm/kg, but by 20% it falls to 0.31 Nm/kg, a reduction of more than 40%. This reduction becomes statistically significant at 10% and continues dropping through 15% and 20%.
This makes incline treadmill walking a useful option for people with medial knee osteoarthritis or those recovering from knee injuries who want to challenge their muscles without overloading the joint. You’re asking your glutes, hamstrings, and calves to work harder while simultaneously reducing a common source of knee stress.