Just as an example, there were evidently reports during the 2007 Glasgow airport attack that someone attempting to subdue the assailant and assist police kicked said attacker in the testicles… but somehow managed to do so hard enough to injure one of their own foot tendons.
Momentum is determined by more than just the strength the muscles put into the movement
Doesn’t take a lot of force to step off a ledge, but you’re still gonna hit the ground pretty dang hard