I don’t know about you, but the thought of spending 30-plus minutes running, using the StairMaster, elliptical trainer, or exercise bike straight bores me silly. The only thing that keeps me going for longer than 20 minutes doing any aerobic workout is to either take a class or to switch it up. For example, I do 20 minutes on one machine, then 20 minutes on another, or I walk, then run, then walk, etc. Luckily, it turns out that interval training, or varying the speed or intensity within your workout, is a good thing. Canadian researchers recently found that alternating four minutes of intense cycling with two-minute rests in between improved aerobic capacity and helped trim fat in a small group of young women. Another Canadian study (they really care about their health in Canada it seems) found that in a group of 16 healthy young men, varying shorts bursts of sprinting then resting offered the equivalent training benefits of more than ten hours of steady, moderate cycling. And in this country, a study of older people who had undergone coronary bypass surgery, one doing interval training on treadmills and stair climbers and the other working out in a slow, steady way, showed that the interval-training group showed greater benefits in endurance. And in practical terms, if you’re running to catch the bus, scoop up your toddler before she stumbles into the street, or racing after your errant pooch, some speed will do you good.