Kristy Wilson, NSCA, NASM: Running on a treadmill allows us to continue exercising when weather conditions aren’t outdoor-friendly or when we want to watch our favorite show while exercising. But it’s not an equal swap for running al fresco.
According to a study, running inside on a treadmill burns slightly fewer calories
My national gymnastics coach use to love to tell me “garbage training equals garbage results.” We don’t hold onto anything running up hills outside (unless we have a great friend willing to drag us up the hill) so treat the treadmill the same way. If there is a need to hang on, lower the incline to a level where you can run hands free.
If used correctly, running on an incline is a great way to increase leg strength and prepare the body for running hills outside. It will also help burn extra calories because running uphill is more challenging and requires the use of more energy than running on a flat ground.
To maximize an indoor run, set the treadmill at an incline that will accommodate your personal fitness level and allow you to avoid having to hold on to the handrails. Using a steep incline is extremely challenging and can place significant stress on the Achilles tendon and calf muscles. If discomfort or pain is felt in these areas, lower the incline level.