Thanks for pushing working out and these kinds of things to skateboarders, really appreciate the efforts. Just some observations that might help some viewers - - For exercise number 1 is a good one but distributing weight across the heel and 1st & 5th toes to make a tripod with the foot would be better for solidifying stability, and in my opinion keeping the knee behind the toes isn't important. - For number 2 he's going too low and his back is rounding too much, keeping a neutral spine through the majority of exercises is a good general rule. - Number 3 should be replaced for an isometric core exercise or upper back mobility depending on what the goal for this exercise was. The role of the lower back is to provide stability and as Stuart McGill (an expert of spine health) says - most people don't need more lower back mobility but they do need more stability, which is the main job of the lower back. - Number 4 is interesting, never tried it but looks pretty challenging, I would just say focus on maintaining that neutral spine throughout the different parts of this exercise. - And for Number 5 focus on keeping that that lower back and pelvis still, move at the hips and upper back, or swap it completely for maybe some regular palloff presses with 5-15 second holds and the feet at the width you'd have them on your board. Hope that helps some people! I've got some exercises for skateboarders on my page if people want to take this further.