Drive knees to the opposite elbow, fast and tight.
Hold your shoulders stacked over your wrists, do not let your hips bounce.
Driving each knee toward the opposite elbow adds rotation to the mountain climber, so your obliques work on every rep alongside the deep core holding your plank together. Done for time at speed, it doubles as conditioning while your upper body holds a strict high plank underneath. That cross-body line is the whole difference. Straight climbers train hip drive, this version makes your trunk produce and resist twist.
The knee path. Straight climbers drive the knee toward the same-side elbow, while the cross-body version drives it across to the opposite elbow, which drags your obliques into every single rep.
As fast as you can while your hips stay quiet and your shoulders stay stacked over your wrists. Speed that comes with bouncing hips is not extra work, it is leaked effort.
Your core is bailing out as it tires. Reset with hips low and level, slow the tempo, and treat every rep like a moving plank rather than a sprint.
