Ninjas are always swinging around on ropes, chains and oversized novelty wheels. These skills demand grip strength, but they also require a more abstract grasp of on-the-fly physics. And while momentum control is largely instinctive, that doesn't mean you can't improve with practice.
Once your arms can lift up your body, good reflexes are mainly about quieting your mind and letting your muscles think. Much like throwing a ball, it's an issue of momentum and release point. Rock climbers and weight lifters often excel on grip-centric obstacles, but there's a reason "ANW" has long been dominated by parkour athletes, aka "free runners." Parkour teaches fluid, improvised acrobatics in any environment, making free runners a natural fit for ninja-grade challenges that often thwart otherwise great athletes.