Just because you are on an anaerobic workout doesn't mean you should haul your treadmill, elliptical, bike, or rowing machine to the dump. You can do more efficient exercises on your old friend by getting your heart rate above the anaerobic threshold – 80 to 85 percent of your maximum heart rate. For optimal results hop on the treadmill and warm up by jogging for five to 10 minutes. When you feel loose, break into your fastest sprint for 15 seconds, then slow down to a casual rate for 45 seconds, allowing your heart rate to come back down a bit. Repeat this pattern for 20 minutes, eventually working your way up to 30 seconds of sprinting followed by 30 seconds of active rest. Your total workout time should take no more than 30 minutes.
See also: The Anaerobic Alternative