To sum it up in a word - surprised. I've been doing static hold/contractions with weighs recently and figured this would be similar. Not so much. It felt very different. I had to chew on why this was for a bit until I figured it out. Let me explain what I came up with by taking the same movement, let's say the triceps extension, and breaking it down for each of the methods.
First is the weighted triceps extension. In this exercise I put 40 lbs on the bar, raise it into the maximum moment arm position (elbow at 90 degrees) and hold it there until my muscles fail and the bar lowers. No matter how long it takes to get to failure, I'm always exerting 40 lbs of upward force on the bar in order to keep it still (I aim for a weight which causes failure in roughly 90 seconds).
|Weighted triceps extension|
|Chained triceps extension|
Was it better or worse? I don't know. I guess I hadn't really though all of this through before hand and it caught me by surprise. In my next effort, I believe I'll try to more evenly distribute my force throughout the rep, but I don't think I'm going to necessarily try to emulate the constant force applied in the weighted exercises. Perhaps I'll just try not to pull (or push) so hard right after the build up phase so I don't have so 'far to fall' on the other side of the curve. It'll be fun to play around with this.
Another thought regarding this topic is that it's probably easier to teach somebody static holds to failure with weights rather than with immovable objects. With the weights there can be no 'cheating'. That is, in order to keep the bar at the same position, we KNOW what the force applied has to be. In the chained case, you could actually bounce up and down with your applied force and still have the chain remain taught. I could easily see a newbie tackling this backwards and try to chase a time under load rather than muscle failure. It's probably more intuitive to hold a weight in place with all you've got until it drops.
And here's the super bonus thought for today. If Work is defined as Force times Distance, then technically speaking, static hold/contraction exercises produce no Work since the Distance traveled by the weight is zero. Thusly, we can correctly call this type of training the No Work Workout