I can monkey at about my mouth level. It's all about upper body and core, at that point. On a lower, waist high monkey, you can use your leg power to lift your hips up high enough to clear the obstacle. But once you start getting chest height and above, you really need to rely on your arms to support your weight, and your core to tuck the knees in and lift the hips behind you. It's all about rising the hips up, to give you enough room to pull your legs through the gap between your arms and the bar. Theoretically, with enough strength, and athlete could monkey anything he could reach.