Free Weights Vs. Machines - A Matter Of Gravity...
We live in a technological age and the exercise machines being designed and manufactured today are better than ever. Your muscles were designed by evolution to overcome the pull of gravity rather than to work against machine resistance, so the biggest gains you will make in building size and strength will come from lifting free weights rather than by exercising on machines.
Free weights also allow people of different heights, weights, and physical proportion (long-armed, short-armed, long-legged, short-legged, etc) to get a complete workout, while many machines seem to be designed only to satisfy those who represent the “average” customer of a commercial gym.
Machines also keep the resistance working along one plane only, meaning that the muscle won’t need to balance and control the resistance. The muscle will react differently if it is constantly subjected to a resistance that comes from varying angles and different directions as opposed to a resistance that come along a predictable line.
I am not against machines as some of them are essential to isolate and fully develop certain areas of your body but I believe that a good programme should include no more than 30% training with machines.