Research proves it: the human body is designed for strenuous, long-haul adventure. Recent studies have even suggested that endurance running actually shaped the evolution of the human body. According to Harvard paleoanthropologist Daniel Lieberman, an author of many such studies and The Story of the Human Body, human beings "are fundamentally adapted to get exercise." But the gym is not enough. "There's nothing like the real thing," says Adam Chase, president of the All American Trail Running Association. The outdoors is simply more demanding. "When you're out on the trail, you have to dance through the rocks and routes." That translates into automatic interval training, which strengthens your heart by forcing it to learn to adapt to just about anything. Here's your guide to getting your heart in shape – and having fun while you're at it.
The steep inclines you'll face amount to built-in intervals of high-intensity work, and the ever-changing pace of biking over difficult terrain gives you the aerobic variety an effective cardio workout should.
Navigating the ups and downs and roots and rocks of mountain biking brings almost every muscle in your body into play: the lower body muscles (calves, quads, hamstrings, glutes, and hip flexors), plus the pecs, shoulders, and even the forearms.
Amp It Up
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Three-time Olympian and U.S. Bicycling Hall of Fame inductee John Howard competes with his training partners. Pick a distant landmark and race to it. Alternate between nearer and farther finish lines to vary the duration of high-intensity work. As your crew gets stronger, reduce the rest periods between races to spend more time clipped in and cranking.