I wondered how much I was “lifting” when doing push-ups. A web search reveals that most empirical tests show men lift about 70-77% of body weight. The physics formula for a Second Class Lever says:
F * FA = R * RA
F = Force (weight I’m pushing)
FA = Force Arm (distance from axis (toes) to hands)
R = Resistance (my body weight)
RA = Resistance Arm (distance from axis to my body’s center of mass)
The Google says center of mass for men usually is typically in the range of 55-60% of height. So, hypothetically speaking, for a six-foot man weighing 210 pounds, with hands during push-up placed about 41/2‘ from toes, and center of mass at 55% of height (40″)…
F * 54″ = 210lb * 40″
F = 155.5 lbs
Which equates to about 74% of my body weight pushed during a push-up. Which falls right in with most empirical estimates!
Thanks for the physics refresher from Exercise Prescription!