The StairMaster is generally considered a low-impact exercise machine because your feet never leave the pedals, eliminating the jarring landing forces you get from running or jumping. But “low impact” doesn’t mean “easy on your joints” in every sense. The stepping motion still places meaningful stress on your knees and hips, especially at deeper step depths, making the full picture more nuanced than a simple yes or no.
What “Low Impact” Actually Means
In exercise science, impact refers to the force that travels through your joints when your foot strikes a surface. Running generates ground reaction forces of 2 to 3 times your body weight with every stride. Stair climbing, by contrast, produces peak vertical forces of roughly 1.1 to 1.2 times body weight during ascent and up to 1.6 times body weight on steeper stairs. On a StairMaster, the forces stay closer to that lower ascent range because you’re only stepping up, never descending, and the pedals absorb some of the load as they sink beneath you.
That’s a significant difference. Your ankles, knees, and hips aren’t absorbing the repeated collision of foot against ground the way they do during a run. In that strict biomechanical sense, yes, the StairMaster qualifies as low impact. Your feet stay planted, the motion is continuous, and there’s no airborne phase where gravity pulls you back down onto a hard surface.
Why It’s Still Hard on Knees
Low impact and low joint stress are not the same thing. Each time you push through a step, your quadriceps contract forcefully to extend the knee, and that contraction compresses the kneecap against the thighbone. The deeper your knee bends during each step, the greater this compressive force becomes. At knee angles above 60 degrees, the effective leverage of the quadriceps decreases, meaning the muscle has to pull harder to produce the same movement, which drives up the pressure behind the kneecap.
For most people with healthy knees, this is perfectly manageable and even beneficial over time. But if you already have kneecap pain or osteoarthritis, you’ll likely feel it on a StairMaster more than on an elliptical or stationary bike. The Johns Hopkins Arthritis Center notes that stairs may hurt but won’t actually harm the knee joint, and that strengthening the quadriceps (which the StairMaster does effectively) is one of the best long-term strategies for knee osteoarthritis. So the discomfort doesn’t necessarily mean damage is occurring.
How It Compares to Other Cardio Machines
Among gym cardio options, the StairMaster sits in a middle zone for joint friendliness. The elliptical trainer has lower loading rates than both stair climbing and treadmill running, making it the gentler option if joint stress is your primary concern. A stationary bike is gentler still, since your body weight is supported by the seat. The treadmill, when used for running, is the highest-impact option by a wide margin.
Where the StairMaster stands out is intensity. It’s rated at 9.0 METs in the Compendium of Physical Activities, which places it firmly in the vigorous-exercise category for most adults. That’s comparable to running at a moderate pace, but without the repetitive pounding. You get a serious cardiovascular workout while keeping impact forces relatively low. Few machines offer that combination as efficiently.
The Muscles That Protect Your Joints
One reason the StairMaster is often recommended despite its knee demands is the muscle activation it produces. EMG studies show that stair climbing generates high levels of gluteus maximus activity during the pushing phase, comparable to compound strength exercises like lunges and Romanian deadlifts. The gluteus medius, the smaller muscle along the outer hip, fires throughout each single-leg stance to stabilize the pelvis and prevent the knee from collapsing inward.
This matters because strong glutes and quadriceps are the primary stabilizers of the knee and hip joints. Over time, regular StairMaster use builds the very muscles that reduce joint stress during everyday activities like walking, climbing actual stairs, and getting out of a chair. It’s a somewhat paradoxical trade-off: the exercise demands more from your joints in the short term but strengthens the structures that protect them in the long term.
Handrail Use Changes the Equation
How you use the StairMaster significantly affects both the workload and the forces on your joints. Leaning forward onto the handrails offloads a surprising amount of body weight. One practical test found that leaning reduced the effective load from 83 kg to 62 kg, a 25% reduction. Calorie burn dropped by 22%, and heart rate fell by more than 10 beats per minute at the same speed setting.
If you’re recovering from an injury and want to further reduce joint stress, light handrail support can be a useful tool. But if your goal is a full workout, leaning defeats the purpose. You’re essentially making the machine easier without realizing it. The better approach is to stand upright with only light fingertip contact on the rails for balance. If you find yourself gripping tightly or leaning forward, that’s a sign the speed is set too high.
Bone Health Benefits
Despite being low impact, the StairMaster still provides enough mechanical loading to stimulate bone growth. Stair climbing increases bone mineral density, particularly in the hips and legs, because it forces your skeleton to resist gravity under load while simultaneously strengthening the surrounding muscles. This effect is especially well documented in postmenopausal women, a group at elevated risk for osteoporosis. It’s one of the few low-impact exercises that genuinely qualifies as weight-bearing, since you’re supporting your full body weight throughout the movement.
Who Benefits Most
The StairMaster is a strong choice if you want vigorous cardio without the repeated impact of running. It works particularly well for people transitioning back from a running injury, those who are overweight and need a lower-impact alternative that still burns significant calories, and anyone looking to build lower-body strength alongside cardiovascular fitness.
It’s less ideal if you have active kneecap pain, significant knee arthritis that flares with stair climbing, or balance issues that force you to lean heavily on the handrails. In those cases, an elliptical or recumbent bike will deliver a comparable cardio workout with less joint compression. If you do have mild knee issues but want to try the StairMaster, starting at a slower speed with shorter sessions gives your quadriceps and glutes time to build the strength needed to support your knees through the movement.