“When we walk we use our muscles to propel us, which increases our energy expenditure, thus increasing the metabolic demands placed on our muscles and the body as a whole.” “The speed at which we walk has an influence, with faster walking resulting in better health outcomes such as predictors of all cause and cardiovascular mortality,” Carson adds. And it turns out that walking doesn't really build size—although Carson points out that in a study where step counts were reduced to below 1,500 steps per day, participants saw muscle protein synthesis reduced by 28%, even after a high protein meal, and significant reductions in leg lean mass.