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The machines are hydrolics and supposedly work you harder the harder you push them... but I'm just not seeing it.
Yeah, see the problem with hydraulic machines is that the level of resistance you get is based on YOU - so there's less of a challenge. Because most of us - whether consciously or unconsciously - after a certain point is reached, cannot maintain the level of pressure/speed needed to get a high amount of resistance.
Whereas with real weights, there isn't an opportunity for you to slack off - 15lbs is 15lbs. So for example, when I'm doing military presses with 2 15lb barbells, by the time I get to my 12th rep, I'm having to FORCE myself to lift them and feeling the burn, but I'm still lifting 15 lbs with each arm. Whereas with a hydraulic machine, by the time you get to that 12th rep and your arms are tired and shakey, you're not moving that much weight any more because you're unable to generate the force that the machine needs. You never have the opportunity to lift to failure because the machine won't let you fail.
Also with a hydraulic machine, and using the example above, it's easier for your dominant arm or leg (say with leg presses) to take over and compensate for a weaker non-dominant arm or leg. And so you might be maintaining some resistance, but not equally so.
Finally just about machines in general is that they work muscles in isolation, not in complex groups. And we don't live our lives working muscles in isolation. So for truly functional fitness, it's better to get away from machines and work with weights you hold and carry - or with your body weight - or with some combination of the two. And do exercises that work groups of muscles, rather than each muscle individually.
Edited: Just found this article which I think explains it better than I can:
http://findarticles.com/p/articles/m...3/ai_113650929
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However, Bryant says, there's a downside. With less of a challenge in the eccentric phase, you won't gain as much muscle strength and won't see as significant an improvement in bone health. Also, he cautions, "there comes a point where the machine doesn't provide enough resistance. Inside of six months, you'll probably need a greater challenge, such as a workout with free weights or with machines that use weight plates."