Compound movements work multiple muscle groups at the same time. examples would be dead lifts, squats, bench press, pull ups. isolations, isolate specific muscles and are usually done with much lighter weights, examples would be preacher bench, flys, leg extensions.

as for the diet, all I can say is if you really want to improve in the gym, your gonna have to suck it up and eat correctly. There isnt much more to it.

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I don't do this for my family, my friends, women, accolades, pride, or ego. I do it for me and no one else, its just part of who I am.