Long bouts of moderate intensity exercise may actually preferentially burn more muscle tissue than one would like . The goal, after all, is usually to burn calories from carbohydrate storage and maintain muscle.
Some studies have found that brief intervals of high intensity training are more effective at maintaining muscle and building their capacity for lactic acid oxidation .
Lactic acid builds up as muscles undergo intense strain. You may recognize this as the burning sensation you might sometimes feel as you’re trying to lift that last rep or trying to sprint the last 100m of a good jog. During the recovery from bout of the high intensity, lactic acid is broken down. This process uses energy from carbohydrate storage or fat . Translation – interval training may be better than a moderate intensity run for losing fat and getting lean.
So next time you’re heading out for your weekly (or monthly or whenever you can get yourself off the couch) run, perhaps head down to the track instead and run 5 or 6 400m sprints, each followed by 2 minutes of rest. It may take less time than a 10k jog, but it may be just as effective.