Walking is a widely accessible activity for maintaining physical fitness. For those aiming to maximize energy expenditure, a common question arises regarding where to take their steps: outside on the pavement or inside on a motorized machine. The environment in which you walk introduces different mechanical and physiological demands that directly influence the total number of calories your body burns. Understanding these differences can help you tailor your routine to meet your specific fitness goals.
The Role of External Resistance in Outdoor Walking
Walking outdoors naturally increases the physical effort required because the body must overcome several forms of external resistance. The most significant of these is aerodynamic drag, or wind resistance, which demands more energy output, especially as walking speed increases. Unlike the controlled environment of a gym, the body must constantly push against the air, which can increase calorie burn compared to walking indoors.
The varying and often uneven terrain encountered outside also forces your muscles to work harder for stabilization. Subtle changes in the road surface require continuous adjustments from the stabilizing muscles in your legs and core. This increased demand for balance and impact absorption elevates the metabolic cost compared to the flat, consistent surface of a treadmill.
Furthermore, the body must expend energy to regulate its temperature when exposed to the elements. Walking in hot or cold weather adds the physiological burden of thermoregulation, as the body works to cool itself through sweating or warm itself by shivering. This additional work contributes to the overall energy expenditure of the outdoor workout. The simple act of self-propulsion, where you must push your body forward over the ground, also naturally requires more effort than having a moving belt pull your foot back.
Adjusting for Treadmill Mechanics
The mechanics of treadmill walking inherently reduce the energy required compared to walking outdoors at the same pace. The moving belt assists in leg turnover, which eliminates the need for the same level of propulsive force required to push off the ground and move your body forward. This lack of self-propulsion is the primary reason a walk on a flat treadmill is physiologically easier than a walk on flat ground outside.
To compensate for the reduced effort, a simple adjustment can be made to better simulate the energy cost of walking outdoors. Setting the treadmill to a 1% incline is widely recommended to account for the absence of wind resistance and the natural variations in terrain. Studies have shown that this slight incline effectively matches the metabolic rate of walking or running on flat ground outside. This “1% rule” is the practical takeaway for those seeking to match their outdoor calorie burn indoors.
A common practice that further reduces the effectiveness of a treadmill workout is holding onto the handrails. When a person grips the rails, they transfer some of their body weight and stabilization work away from their legs and core, significantly decreasing the workload. Holding the handrails, particularly when leaning backward, can reduce the metabolic cost of the exercise by over 30%.
If you feel the need to hold the handrails for balance, it is usually an indication that the speed or incline is set too high for your current fitness level. To maximize the calorie burn and maintain proper walking form, it is better to lower the speed or incline and walk hands-free. If you must use the handrails, maintaining an upright posture rather than leaning back will prevent the most drastic reduction in energy expenditure.
Reliability of Calorie Tracking Devices
Both commercial treadmill consoles and personal fitness trackers provide an estimate of calories burned, but these figures should be viewed with caution. These devices rely on generalized formulas that use basic inputs like weight, height, age, and heart rate to calculate metabolic expenditure. They do not directly measure the body’s actual energy use, which requires specialized laboratory equipment like indirect calorimeters.
Research has shown significant variability in the accuracy of these consumer-grade devices regarding energy expenditure. Some wearable trackers have been found to be inaccurate by an average of 27% to over 90% when estimating calorie burn. This substantial margin of error means the number displayed is an approximation, not a precise measurement of your workout’s effect.
Treadmill consoles are similarly limited, often using a standard algorithm that may not fully account for individual differences in walking efficiency or the effect of holding the handrails. Rather than focusing on the absolute number of calories, it is more useful to track these figures as relative measures of effort over time. If the number increases for a similar workout duration, it suggests an increase in intensity, which is a better gauge of progress.