The American College of Sports Medicine reports that you can elevate your metabolism for up to 24 hours post-exercise by adding just one little twist to your exercise routine. All you have to do is inject brief periods of intense effort into your regular walks or runs, bicycling, elliptical sessions, etc. The intensity effectively resets your metabolism to a slightly higher rate during your workout, and it takes hours for it to slow down again. That equals ongoing calorie burn long after you've showered and toweled off.