Exercise makes waste—and not just laundry and power-bar wrappers. It leaves our insides looking like a short-staffed restaurant kitchen. Rest gives our body a chance to clean up the mess.
Hard or vigorous exercise creates a ton of waste because it uses energy so fast and in such large amounts. As the waste builds up, we become less efficient at the work we’re doing. Rest intervals give our bodies the chance to buffer, or process, this waste and get it out of our system.
Take, for example, a waste like carbon dioxide. When we work hard, we accumulate more CO2 in our blood, and our body has to get rid of the excess. When we take a break, our breathing continues at a high rate to that’s accumulated. Other waste products take longer to process, which is why a 48-hour break is common between very intense training days.
Prolonged exercise—think marathons or other long cardio sessions—is less intense but still creates a buildup of waste because it goes on for so long. As we fatigue, our body becomes less efficient at clearing it away. These types of activities don’t need rest intervals, which is why recovery days (or weeks) afterward are so important.
Rest + sleep