Rev up your metabolism by alternating your speed and intensity during aerobic workouts. Not only should you alternate your routine to prevent burnout or boredom, but to give your body a jolt. If you normally walk at 6.5km/h on the treadmill or take 15 minutes to walk a km, up the pace by going at 8km/h for a minute or so during your workout. Do this every five minutes or so. Each time you work out, increase your bouts of speed in small increments.