lets see. second law says fnet=ma(observed) so mass times acceleration is uh, the total force being exerted. if there is no acceleration, ya ain't doing any work. more acceleration, more force being outputted so if you move fast on exercises then you gots lotta force,. Eh???
Then the third law says everything comes in pairs. equal and opposite reaction thing. so you pull down on lats, the bars pull back on you equally. so check it: if a car runs into a semi, the car gets squashed but not the semi even though the semi got it as bad as the car. the difference? the semi's bigger. Yup, i think that's it!