Clinging onto tiny molded plastic nubs, members of the Outing Centre scaled walls Friday night at the Northlander Climbing Gym in Rockford, climbing sometimes more than 30 feet in the air.

Experienced climbers pushed with their legs and balanced with their arms to conserve energy, while rookies scrambled up the walls quickly, pulling and pushing with their upper bodies.

-Soon the scrambling dissolved into a slow crawl and the weak, inexperienced climbers popped off the wall like dead flies, only to be caught by a pulley, a belayer below, a jockstrap-esque harness and an International Climbing and Mountaineering Federation-approved rope that can withstand the weight of a car, said Ben Kinney, an Outing Centre trip leader.

“Their lives are in our hands,” said Karen Rosenbloom, an Outing Centre trip leader.

The spotter below, known to experienced climbers as a belayer, lowers the defeated climber from off the wall, feeding the pulley rope in between a two-hole piece of Air Force-grade aluminum.

Prior to climbing, a climber will check the harness straps of the belayer and vice versa. Then the following conversation will ensue:

“On belay?” a climber will ask, checking with a belayer to see if his or her equipment is ready.

“Belay on,” the belayer will respond.

“Climb?”

“Climb on.”

As the climbing walls progressed in difficulty, the molded nubs of plastic became smaller, fewer and farther between. Hence more and more climbers popped off the walls, dangling mid-air. The dangling, exhausted climbers shake subtlety; experienced climbers call this “The Elvis,” Rosenbloom said.

Most fallen climbers fell only a few feet until a belayer caught and suspended the dangling climber mid-fall. Then, the climber had two choices: swing back to the wall and ascend or quit and be lowered.

“It’s about beating your goal. Once you beat it, the next one starts. And then the next. It never stops,” Rosenbloom said.

On the back wall, experienced climbers bouldered, or scaled a wall horizontally, in the back of the gym.

Bouldering differs from regular climbing. Joel Brown, an Outing Centre assistant trip leader, said bouldering is harder, more technical freestyle work, done only a few feet (and up to 12 feet) off the soft, shredded rubber tires lining the facility.

Bouldering courses are lined with irregular climbing nubs, some in the shapes of skulls, others in the shapes of hands. The bouldering walls break and bend at sharp angles.

Boulderers spot themselves with a black, 6-square-foot foam pad and move slowly across the territory. They hang, arms outstretched, in a skeleton-hang to conserve energy, Brown said.

And everyone else is either on the ground staring skyward or scaling up the indoor climbing walls, scrambling and stretching hopefully for that next tiny plastic nub.