So this was fun...400 non-stop hits with a 40 lb sledgehammer. Took a little over 17 minutes start to finish. I sped the video up 17X so it would fit in one minute. My grip was TRASHED at the end of it. Serious total-body training...even my hamstrings were feeling it by the end. The sledgehammer is from Stronger Grip LLC - the head is loadable. I have two half-tires strapped together and anchored so that they don't move as much (and don't tip over, which has happened with a single half-tire), si