Gliders are sneaky: They look really fun (because they are slippery and slide across the floor!), but they go from zero to 100. Why? They force the body to use a different movement pattern than it's used to — think a traditional reverse lunge where you step back and down versus one with a glider in which you slide the foot back — so you're engaging different muscles. The slippery bottoms are also destabilizing, so the body is constantly under tension. Which is a good thing: “The longer your muscle is under tension, the harder it’s working because there’s no rest,” says Lau. Her go-to exercise? A plank to pike to work your core and upper body: Start in a plank with straight arms, pike your hips up in the air and slide your feet as close as possible to your hands and release down again. Repeat.