Got six minutes?

Got no time to exercise? No bucks for a gym membership? Dr. Martin Gibala, pictured above practicing what he preaches, suggests that a series of 30 second sprints -- four to seven per exercise session for a total of three sessions per week -- can turn your muscles into lean, mean, metabolizing machines.

So here's the catch. Between each sprint, you should sit on your exercise bike and just suck air. So we're talking about a 20 minute commitment three times weekly, each workout made up of six intense bursts of activity separated by a few minutes of recovery. Then poof! sweet, guilt-free release, on to the rest of your day.

At the end of two weeks or 2 1/2 hours total of this on-again off-again stuff, your muscles will show the same increase in citrate synthase --an enzyme that reflects the ability to utilize oxygen-- as a bunch of hooples who actually wasted 10.5 hours in that same time period cycling nowhere. Furthermore, adds Gibala, you'll get the weight loss benefits as well:

People forget that if you do a 30-second hard spurt your body continues to burn calories during recovery; just because you have physically stopped racing doesn't mean the effects of the workout are over.

So now what's your excuse?