UNLESS YOU PAY FOR AN HOUR on a diagnostic treadmill, you may never know for sure whether your VO2 max (the volume of oxygen your muscles can use at maximum exertion) is a humble 65, or approaches the sublime 90.2 of mountain runner Matt "Oxygen Is Overrated" Carpenter. The higher the number, the longer you last, be it on skis, singletrack, or the wall. But whatever your score, you can raise itand it won't require endless hours of exercise. Enter high-intensity intermittent training (HIIT, so dubbed by the Brits; intervals to us Yanks). "Studies have shown that such training improves VO2 max, lactate threshold, and economy, faster than steady endurance training," says Joe Friel, author of The Mountain Biker's Training Bible. Interval training is hardly new, but recent studies have shed new light on how effective it can be. In just two weeks, one study found, you can lift VO2 max by 11 percent. In another study, participants put in just four minutes a day on the bike (eight 20-second bursts separated by 10 seconds of rest) and saw their VO2 max improve by 15 percent in six weeks. Simply put, you can get 20-mile legs (and lungs) by adding as few as four briefly separated 30-second sprints per workoutabout as long as you need to take out the trashto your existing training plan. Here's how:
Climbers and mountaineers should put in the sprints on stairs, a stair climber, or a stationary rower; runners and cyclists, if you can't get outside, get on a treadmill or stationary bike. Start with two 15-second bursts at your hardest intensity, separated by 30-second rests. Follow this with two more 30-second bursts with 30 seconds between them. Short rest periods30 seconds or lessfor at least half the intervals are the key to the benefits, say researchers. Take a day off, and do the same routine the next workout. Alternating one day on and one day off, add an additional 15- and a 30-second burst every other session for 28 days. Zoom!