Punching hard is a demonstration of power not just strength. There are big bench guys that punch like pillows and some professional boxers with a huge punch that couldn't bench 250lbs. The physics are how fast you can unleash that strength that is an illustration of power. You would think power lifters doing their half hip lock squats with 800lbs could easily dunk a basketball yet many of them have a lousy vertical leaps because they don't have power. Olympic lifters have a vertical leap because they train for power accelerating the bar upward with their pull. The bench with your back braced against a bench is one of the most over rated exercises to increase athletic function. If you want to hit hard punch a heavy bag, explosive pushups, military presses, power jerks, medicine ball drills, and punching with elastic type bands.