What running, stair climbing, and incline walking really do for your body

Biomechanics research comparing walking–and running shows that joint angles, loading rates, and muscle forces differ significantly between the two gaits. Walking, even at an incline, keeps at least one foot in contact with the belt at all times, which reduces peak forces and usually produces fewer overuse injuries when training volume increases. Running, by contrast, involves a flight phase and higher vertical oscillation, which amplify impact and can strain structures like cartilage-and tendons if recovery is inadequate.

Stair climbing occupies a middle position. The vertical work raises muscle force in the legs, yet the absence of a long flight phase may reduce some of the impact seen in running. However, because the movement is very repetitive–and knee flexion angles are large, people with patellar or front of knee pain sometimes find stairs aggravating if they do too much too soon.