WHAT IT IS
Bouldering is a demanding form of climbing performed without ropes. Similar to indoor rock climbing, participants ascend large indoor, man-made boulders (get it?) using a series of short, dynamic individual moves or sequences, rather than the less-demanding endurance-based style of climbing from point to point. "We're trying to find the hardest way up," says Bill Baer, director of climbing at the Manhattan Plaza Health Club. "You could always walk around and climb up the back side of the boulder, but we're trying to find the climb within the rock."
WHAT IT WORKS
Virtually everything. Like most forms of climbing, bouldering hits your hands and forearms the hardest, with your arms, shoulders, and upper back a close second. Your legs will ache, too — and your core will not be overlooked. "Your arms are going to hold on," he says, "but your core is going to hold you in to the wall, which is going to create more efficient climbing."
WHAT TO EXPECT
Your first class will focus on technique. Most newbies attack the rock head-on like a ladder, but positioning your body sideways to the wall is key. You'll also work on maximizing your holds and getting comfortable on the boulder. Show up well hydrated and get a solid warm-up in, because bouldering is a grueling sport with few breaks and little downtime. First-timers are usually maxed by the end of an hour-long session. "You use your muscles so much and they're contracted so hard that when you go to pick up a pencil later, it's hard to hold properly," says Baer.