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.
Cross-country skiing is such a lung-busting workout that an entire sport, the biathlon, was designed to test an athlete's ability to fire a gun – and hit a target – during a cross-country race. (No surprise, then, that it's such a calorie inferno.)
Because the sport involves moving your extremities in relationship to your core rather than to gravity, your shoulders, core, glutes, hamstrings, and calves work constantly.
Amp It Up
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Champion skier and coach Nathan Schultz suggests counting your strokes across a four-minute course. Every time out strive to reduce your stroke count. You can also try skiing without poles to focus on your legs and core.