I'm starting a new job in a couple of days and moving to Brooklyn right after Thanksgiving. I'll try to keep up the blogging, but I can't really make any promises because I'm going to be super busy! In the meantime, here's a short article on strength curves:
I just watched a promotional lecture about an exercise machine that's being made available for home use in a little while, the ARX Fit Omni. I'm not endorsing the machine or suggesting you buy it - I don't even know how much it costs - but I thought it was based on some interesting principles, like the Nautilus system developed by Arthur Jones, and I figured it was worth some discussion.
The ARX and Nautilus equipment are based on making the most efficient use of the strength curve. If talk of curves and math give you anxiety attacks, relax, I'll make this relatively simple!
The strength curve just means that in any particular movement you're going to be able to exert more force in certain parts of the movement than in others - because of the way your body is designed, the direction of gravity relative to the direction of the motion, and whether you're lowering or raising the weight.
This is easier to understand with an example. Take the barbell curl. You pick up a barbell in your hands, with your arms hanging straight down, the the bar is against the tops of your thighs, your body pretty much straight. Keeping your body still and your elbows in the same spot you lift the bar up to your chest, then lower it. All that's happening is that your elbows bend.
Okay, now what's the deal with a strength curve? Look at that movement. Will that movement feel equally hard at every point along the path? No, it won't. At the bottom of the move you're almost swinging the bar forwards - you're not really fighting gravity. At the top, the same thing happens. It's the middle - when your elbows are bent at a right angle - where the movement is the hardest. The other thing is that you're always stronger eccentrically than concentrically. In other words, you can safely lower more weight than you can lift.
What's the big deal, you ask? Well, the big deal is that if you do barbell curls you're never going to maximally stress yourself at all points along the movement going up and down. If you use enough weight to make the first few inches difficult, you'll never get the bar past the midpoint. If you use enough weight to make the lowering really stressful you'll never be able to lift the bar. In effect, you're wasting a large part of the motion, and you're never going to maximize your strength anywhere but in the part of the path where the resistance is actually right for you.
Traditionally you would get around this by performing multiple exercises that each stressed you in a different spot or a different part of the range. You might do incline curls to work the lower part of the move. You might do negatives - where someone helps you lift the bar, then you lower it on your own, to work the eccentric portion of the movement more optimally.
Ideally, we'd like to have a magic bar. Imagine a bar that was heavier at the bottom, then got lighter - not too much lighter, just lighter enough that you could curl it through the midpoint - then got heavier towards the top. then it would get a lot heavier as you lowered it, again being not as heavy through the midpoint but heaviest towards the bottom, while lowering it. And the magic bar would know by exactly what amount it should get lighter or heavier for each individual user.
That's what Arthur Jones tried to do with his Nautilus machines. He used a cam - a funny shaped axle, basically - that would change the radius from the axle to the chain depending on where in the movement you were. The details aren't important, but instead of a machine where it took X pounds of force to move the bar, it would take more than X to move it through some angles and less than X to move it through others, more or less matching the places where you were naturally stronger or weaker.
There were (and are) problems with Nautilus equipment. If you had longer or shorter limbs than average the strength curve might still not match your own. And it didn't automatically get heavier for the lowering portion - though they were often made so it was really easy to do negatives on your own.
The ARX Fit Omni has a machine that varies the resistance on a belt depending on instructions given to it by a computer. I don't know how it matches your strength curve - if it "learns" how much force you can exert or uses mathematical modelling - I'm not suggesting that it does or does not work. It does seem very interesting. It promises an exercise that would maximally stress you through every degree of a range of motion - not be really hard at some sticking point and relatively easy elsewhere.
If it works the workouts it induces would be very efficient and promise good hypertrophy and strength building in a very short period of time. I have a feeling it's going to be too expensive for most of us to have around the house, but that's just a guess. If you get to play around with one let me know how it works!