you are absolutely correct w/ using heavy weight and low reps to gain size and muscle mass. You are also correct about using low weight and high reps to tone up and lose weight.
But I was referring to the actual form of exercise. Free weights vs. machines & cables
If you want to gain size and muscle then you do heavy (manageable) weight at low reps. Free weights are the favorite for this b/c often times machines do not have enough weight on them to select. If you want to tone and lose weight then you do light weight and high reps.
Machines while they do limit your form to a certain degree, they are designed to keep your form exact. Meaning you can't cheat. What I mean by this is do you ever go to the gym and see the wana-be tough guys trying to curl huge amounts of weight w/ free weights
way beyond what they are safely capable of lifting ? They often swing their body and use their back to complete the rep. Not only is their form totally wrong but they are also risking injury.
