They are adjustable to your height but once you are locked in the weight only moves in the fixed direction of the cam. Take 2 identical twins and train one on machines only and the other on free weights only for 90 days. Then switch the training programs and you will see the twin who trained on free weights for the first 90 days will be stronger in both lifts (the machine and free weight squats) and the twin who did only machine work the first 90 days will be significantly weaker.
I always ask for examples of a professional NFL or NHL team that uses primarily machines for their strength training programs because none exist. Why is this so? If machines made athletes so much stronger why wouldn't a strength coach train his athletes that way?
The idea of the cam is not about fixed or free direction but rather to provide variable resistance to match the strength curve of the joint movement.
You are incorrect in your analogy regarding twins and free weights versus machines. I did it on myself. At one point I was able to bench press 315 pounds for 7 strict reps. All the way down, touching the chest, and with a slight but distinct pause. I stopped benching for about three months doing a machine, I don't remember which one, that pretty much simulated the exact movement and picked a weight that I could do about 8 reps before failing at the 9th. I don't remember what weight but let's just say it was 200 lbs that I was using on the machine. I do remember that over that three month period I increase the resistance by about five plates for 8 reps, presumably, that was 50 lbs so let's say now I was doing 250 lbs.
When I went back to the bench press I found that I could barely eke out 4 reps. This made no sense to me. I mean, how could I have gotten weaker? I went from 200 to 250 lbs using the same muscles in pretty much the same way but now I can't bench like I use to. Anyway, that convinced me to stick to the bench press. No matter what logic told me the fact is I got weaker. Empirical evidence always trumps logic and reason.
It didn't take that long to get back my original strength performance on the bench. I was back to benching 315 for 7 reps in about five weeks. I was pretty much maxed out on the bench for my body type. I've long accepted the fact, albeit begrudgingly, that I was not built to perform great feats of strength. Then one day, maybe almost a year later, I went back to that bench machine just to mix things up a bit. Shockingly, I found that I could barely budge the 250 lbs for more than three reps! Again this made no sense to me. Did I get weaker again.
I believe that in both cases I didn't really get stronger or weaker per se but I got stronger or weaker in that particular movement. I think your body is very activity specific. Getting better, stronger, more stamina in one activity doesn't necessarily directly transfer to another. You lose that specific skill. You get "out of practice".
I always considered marathoners to be the ultimate endurance athletes. Compared to what they do, anything else, from a conditioning perspective, is a piece of cake. I remember training in BJJ with an avid marathoner. What shocked both him and myself was how winded he got. He couldn't keep up stamina wise. Now there is no way on Heaven and Earth that I could run a marathon but on the mat I made him look out of shape.
I've experienced this phenomenon, not just with weights where I would get "weaker" despite always being in training on a movement I stopped doing for a while, but also when I would switch up running stairs to running the sand hill. Or swimming versus jogging. I was able to do more for longer, or less for shorter, not necessarily because my conditioning improved or diminished. I was always in training and always in top shape. But because I simply got better or worse in that particular movement.
The legendary wrestler, Dan Gable, know for his superb conditioning and being tireless on the mat was once asked what is the best exercise to increase endurance and stamina for wrestling. He simply replied, "Wrestling".
