EVERY MORNING AS YOU roll out of bed and stand up, a continuous neurological process works to keep you upright: Sensors and receptors in your joints and muscles send messages to your brain about where they are in space; your brain then analyzes the data and sends the appropriate response to the small stabilizer muscles that keep you vertical. This process is called balance, and to avoid disaster while spinning down a winding slice of boulder-strewn singletrack, it must be fine-tuned far beyond the ability to stay on your feet every morning.
"Improving balance," says Bernard Petiot, training director for Cirque du Soleil, arguably the most preternaturally proprioceptive group of people on the planet, "is a matter of systematic and progressive exposure to unbalanced situations." Outdoor athletes tend to do this naturally as they learn new sports. "If you look at skateboarders, climbers, and snowboarders," Petiot explains, "they will progressively increase the complexity of what they are doing." But to develop the general system as a whole, you need to put in time at the gym.
Specifically, Petiot prescribes taking many of the strength-training lifts you've already learned in the SYL program—flies, squats, lunges, etc.—and further destabilizing them on a wobble board, a platform designed to make you feel like you're standing on a ship while performing each exercise (see "The Body Shop"). Starting in week 17, you'll add balance lifts to your Tuesday/Thursday strength sessions (see "Balance Exercises").
But balance is only half of the final equation. To round out your fitness arsenal, you need agility, which from an athletic standpoint is your ability to remain graceful on the fly while making quick stops and starts. "For outdoor sports," says Peter Twist, a conditioning coach to NHL and NBA athletes, "a lot of your training is very linear—cycling or running in a straight line. But most of the situations for which you need agility are multidirectional, with a lot of sudden changes in direction."
To get you off the straight and narrow, you'll add three agility drills to your Monday and Friday plyometric sessions (see "Agility Exercises,"). In addition to traditional shuffle-step drills, this means playing catch with an exasperating toy called a reaction ball, which bounces in unexpected directions. By the end of the month, you'll be quicker, better grounded, and less likely to take a humility walk through your drugstore's elastic-bandage aisle.