@lyndon1996 Core is strong, I can do L-sit for 15 seconds. I do L-sit pull-ups, am working on the V-sit, and have a 5-minute plank hold. Can plank 1-minutes with 45 lbs on my back. Side planks and hollow earths. Yada yada. So that's not it. I think it's weak ankles, knees and perhaps...