accelerometers vs gyroscopes

Hi my name is alaa hany, i'm graduating and my graduation project is about an applications that has information about enhancing working out in the gym and adjusting the positions, my question is , i don't know much about acceleometers and gyroscopes ,and the adjusting part will check if the person is holding the weight in the right angle and he was let's say bending a little it will alarm him in order to fix his position. so which one of them should i use ??!!