Hmm I'm probably overdoing the force. I have a ~100 lbs bag tucked up against a corner, so it can't swing, but it's just becuse I have too little space to dedicate for the bag. Yet, kicking that nonmobile bag is butter compared to the impact kicking into someones knee blocks or shins, even with shin pads, which happens regularly in fight, the last bone bruise took more than a 1-2months to heal but its now good so i cna kick hard again. I hope I learned some lessons also from the bruises, but getting permanently hurt would be bad.Some years ago i was reading one of He Il Cho's books where he was addressing kicking the heavy bag and opines that you should not be kicking any bag over 100lbs. saying it put too much strain on the joints and IIRC 60lbs is enough to develop power.