The setting labeled “incline” on a treadmill refers to the upward slope of the machine’s deck, simulating walking or running uphill. This percentage represents the grade of the slope, directly influencing the intensity of the workout. A 12% incline is considered a significant grade, transforming a moderate walk into a high-intensity, low-impact training session. Using a high incline is an effective method for increasing exercise difficulty without relying solely on faster speeds, which can be harder on the joints.
Visualizing the 12% Grade
The 12% grade on a treadmill physically represents a steep hill climb in the real world. This percentage means that for every 100 units of horizontal distance traveled, the elevation increases by 12 units vertically. A 12% grade is substantially steeper than the slopes found in most urban environments, such as sidewalks or ramps, which typically do not exceed 8%.
While treadmills display the incline as a percentage grade, this value is mathematically different from the actual angle in degrees. A 12% grade is equivalent to an angle of approximately 6.8 degrees. Many treadmills will max out at around 15% incline, positioning the 12% setting near the upper limit of the machine’s difficulty.
The Physiological Impact on Effort
Walking or running on a 12% incline dramatically increases the physiological demand on the body compared to exercising on a flat surface. This steepness requires the body to shift its effort from primarily horizontal propulsion to a more vertical lifting motion against gravity. The immediate result is a significant elevation in the heart rate, pushing the cardiovascular system to work harder to deliver oxygen to the working muscles.
The Rate of Perceived Exertion (RPE) also climbs quickly, meaning the exercise feels substantially more difficult than the same speed on a flat surface. This increased effort is because the body must stabilize itself against the slope while simultaneously performing the work of lifting its weight uphill. Because of the greater resistance and higher muscle engagement, the overall caloric expenditure is significantly boosted. For example, walking at a moderate speed on a 12% incline can burn an estimated 30–40% more calories than walking at the same speed on a 0% incline.
Proper Stride and Posture for High Incline
Posture and Gaze
Using a 12% incline effectively and safely requires specific adjustments to one’s movement mechanics and posture. Maintaining an upright torso is paramount, as the instinct to excessively lean forward should be avoided. Instead, the body should stay vertical to the ground, or slightly lean into the treadmill deck from the ankles, which helps utilize the correct muscles for the climb. Looking down at the feet is also detrimental, as it can strain the neck and restrict the airway, so the gaze should remain forward.
Stride and Handrail Use
The foot strike changes naturally on a steep incline; you should focus on landing with a natural stride, avoiding a long, exaggerated step. Rather than a hard heel strike, the focus should be on a quick foot turnover and a powerful push-off from the toes to propel the body upward. A common error is holding tightly onto the handrails for support, which reduces the workout’s effectiveness and compromises posture by causing the user to lean back. Handrails should only be used lightly for momentary balance, not to support body weight, as relying on them can reduce the calorie burn by up to 20% and negatively alter the natural gait.
Specific Muscle Group Activation
The steep pitch of a 12% incline fundamentally alters which muscle groups are primarily recruited compared to walking on a flat surface. This grade significantly increases the reliance on the posterior chain, which includes the muscles along the back of the body. The gluteal muscles and hamstrings are activated more heavily to generate the force needed to propel the body upward against gravity.
The lower leg muscles, specifically the calves, also experience a substantial increase in workload. Because the foot is constantly pushing off the steep slope, the calf muscles work harder to achieve the necessary ankle extension with each step.