Now, before you think I'm wishing myself back to the 70's, where most machines were ergonomically incorrect in one way or the other, let me first say that I truly welcome and applaud the ingenious development of exercise machines in the past decade. Hammer Strength, for one, revolutionized the industry with their excellent line of machines.
Today we have well-engineered machines, that not only makes sure that we hit the muscles from right angles, we are also allowed free range of movement and support at critical points, so that we run lesser risk of injury. For example, a good leg-curl machine of today makes it natural to keep a straight spine, instead of the extreme arch you saw everywhere only 10 years ago (which puts extreme pressure on your lower back, by the way, which can lead to plenty of trouble down the road. Now we can avoid that.)
So...These are the good machines. Unfortunately, there is a whole bunch of machines put together by people who either have no clue of biomechanics, have a complete disregard for the customers except for their wallets, or a combination of both. Real life example: The Hack-squat for the Hunchback of Notre Dame!
At the gym where I train, there is a variety of hack-squat machines. They're all of different makes. All of them are slightly different, but one stands out from the crowd. The reason for this is the pad on which you normally rest your head. In all the other ones, that pad is basically an extension of the big pad against which you rest your back while squatting away. Not in this case. Instead, some yahoo thought it was a brilliant idea to take that pad, weld it to a 4-inch steel bar, and arrange the whole thing at a 30 degree angle against the rest of the pad. If you stand up straight and look down at your toes, you get the angle you end up with in the neck. Now, imagine putting on a couple of hundred pounds of pressure on your shoulders. Say hello to some serious upper-spine problems.
The bottom line is that you end up in a position like Quasimodo, and no, I've never seen a single person use that machine more than once. Why? Because some dork actually thought it was worth getting out of his way to make an addition that renders the whole thing unusable.
...I think you're getting an idea of what I'm talking about here. If you look around, you'll spot plenty of these four-digit numbers of dollars dust-collectors. Or worse yet, some machines are crap, but are still being frequently used! These are the ones that are either completely ineffective, or obvious low-quality rip-offs from a reputable manufacturer. A good example of the first is the classic:
The Useless Leg-Machine
Actually, there are usually two versions: An adductor and an abductor, where you either push your legs apart or pull them together. Now, even though they are Ok machines at what they do, they're really pretty useless in building an all-round physique. From a practical standpoint, it's pointless - do squats or leg presses, and get a natural motion with natural use of the muscles!
From a cosmetic standpoint, it's counterproductive - as you can't spot-burn fat, all a person with, say some extra fat on the inner thighs would achieve, is to add muscle UNDER the fat, making the whole section look even bigger!
I asked a gym owner once why he invested money in buying new adductor & abductor machines when he knew that they were perfectly useless, and he explained that it was because of the female clientele. Basically, if he'd throw out those machines, he'd throw out the better part of his female clientele as well.
I'm guessing it's the same psychology that makes fat men do thousands of crunches in the hope of getting ripped in spite of their diet of donuts and cheeseburgers. I'm not a psychologist, but I DO know that using the abductor/adductor machine to "get in shape" is a BIG mistake! Once and for all - training a muscle does NOT burn the fat covering it! Spend the time on a Stairmaster instead!
Ab machines are frequently used, almost regardless of how it's made and how it works. Even the worst back-killer or hip-flexor trainer gets used, as long as the sign on it say it's an ab-machine. The seated versions often put undue stress on the lower spine, but at least they get the job done of mangling the abdominals. The REAL bandit is the hanging leg-raise kind of machines there are out there!
As you well know by now, the only way to properly train a muscle is to decrease the distance between its two insertions. Plain and simple. Your biceps won't grow from you just flexing it statically - you need to actual curl the weight up and down so that the muscle can contract and stretch out.
So, why bother doing hanging leg-raises, or use any machine that simulates that motion? Your hip-flexors are working overtime, and in order to counteract them, the abs is working statically to keep your spine from snapping like a twig. That static tension causes lactic acid buildup, which is mistakenly interpreted as the abs getting a good workout.
Forget it! In order to train your abs, you must decrease the distance between your pelvis and ribcage, as in a good, ol' crunch! There's simply no other way!
So, forget all the fancy hanging-arrangements to strap your arms in, or machines where you're lying on your back and swinging your legs up and down. Crunches will get you what you want 10 times faster. And guess what? Crunches done on a mat on the floor are free! But I guess the manufacturers don't want you to think about that.
Today, most back machines are of good, if not excellent quality. They're engineered to target different areas of the back, and make excellent partners with dead lifts and dumbbell rows in a good workout. However, once in a while you see a real back killer. At my gym, we have two.
Back killer #1
This is basically a sort of 45-degree angled version of a simple seated row. However, you're supposed to stand and balance with your feet on a pipe a few inches above the ground, lean your butt against the angled pad, and - according to the instruction - round your back as much as possible when rowing (the handle is down right in front of your feet). Umm... Do I even have to comment on this one?
Back killer #2
The T-Bar row is a classic. Many big-name bodybuilders have, and still swears by it. I say these guys should think again. Consider your positioning. You're standing in a very vulnerable position, bent over, and with the weight in a fixed groove that is supposed to fit everyone. There's no such thing as a "universal" solution for something like this. What's more, even if you luck out and find that the T-Bar is as made for you, you still put tremendous amounts of stress on your spine.
Now, correct me if I'm wrong, but the point is to train your muscles, or more specifically, the traps, lats, and rhomboideus, right? Why complicate matters, when you can do the exact same movement with a rowing machine with a chest-pad that takes the stress off your spine? (You know the kind - it's essentially the same as a T-Bar, but it has a pad for you to rest your chest against!) If your gym doesn't have one of those, you can still substitute the T-Bar rows with some good old dumbbell rows. Hey, at least you can support your upper body with the other hand!
Most calf-machines are really basic, and are therefore hard for a manufacturer to screw up. Hence, most of the ones out there work pretty well. With one exception. This exception is a peculiar-looking little foot-strap-thing that is usually placed rig ht in front of a wall. If you've never seen what I'm talking about - Good, you haven't missed a thing! If you do have seen it, you've probably seen the illustrated chart that goes with it as well.
To be quite honest, my imagination stops short of figuring out how someone could actually build huge calves from this device. The basic idea is that you stand pressed against the wall with your calves flexed to the max (they stay contracted all the way through - you're pretty much standing on your toes!), and keep flexing them while pressing yourself against the wall. I hate to break it to them, but the principle of working a muscle through its full length, as described in the part about the ab-machines, holds true for calves as well.
Don't get me wrong - leg extensions are great! It's close to impossible to cheat, and you can be sure to target the quads 100%. That only makes it even more sad when some manufacturer figures out a way to drastically cut the effectiveness and increase the risk of injury. For example, we know that in order to get a full stretch of the quad-muscles, we have to let the feet go pretty far back under the seat. If there's a built-in STOP when your knees are in a 90-degree angle you're not even close to stretched, so why did someone go through the extra effort of placing a stop instead of letting the pad travel freely?
Even worse, I've seen a machine that didn't have an adjustable back-pad. Big deal, you say? Well, consider that you should always keep the back of your knees approximately 3 fingers out from the seat in order to avoid putting undue strain on your knee joint. When you're forced into a set position, about 80% of the users are in a less than optimal position, and perhaps 10% in a downright dangerous position.