It has to do with the type of tissue being recruited. You want to recruit the fast-twitch as much as possible, since they're the ones that make you hard and strong. The slow twitch have smaller motor units, and tend to be recruited first. Hence the problem.
See? That's the problem. You want to get to the fast twitch, but they won't kick in unless they're required AND the slow twitch are all firing. A slow movement is no problem for the endurance fibres. As long as the force is low, they won't need to recruit the big guns. And the force will be low, given the duration of the lift.
Actually the speed of the muscle contraction has nothing to do with what type of fibers are recruited. It is the force requirement.
I don't think you necessarily missed this point, but I want to clarify the first statement which references slow movement and endurance fibers.
Ah, thanks for that. I'm still learning this stuff.
I understand the force requirement - with force being mass x acceleration. I also understand that fast-twitch - with their larger motor-units - are recruited some time after the slow-twitch are firing, and that with a low-force movement, very few fast twitch will need to engage. Slow twitch of course are well-designed for sustained, low-force movement. Hence my statement. Hopefully I now either sound like I DO get this, or you'll let me know where I'm off.
I find this stuff fascinating, and I appreciate your coming in to explain it.
I also grew up on Duncan Donuts, and your user name makes me homesick for Montreal... <sigh>
One thing I'm not clear on - you mentioned it's not the speed of the movement, but the force requirement. Thing is, as I indicated above, force is mass times acceleration. I realize that at a constant speed, there is no acceleration - but explosive movements are not constant speed for very long!
For example, a boxer's jab is designated by acceleration. They are primarily performed by slow twitch fibers. Secondarily, a hook or uppercut would be slower but depend on more "fast twitch" despite the slower speed of movement.
Makes sense - low force vs high force. Nice example.
Something I've wondered about is recruitment in fast eccentric movements. How is it that these "work" - is it just the generation of microtrauma, or is it again recruitment of fast twitch? The reason I ask is that my delts blew up when I started doing hang cleans. Not clean and press, just the cleans. My feeling is that it was the sudden tug at the insertions that occur at the bottom of the movement - at the start, and again at the finish when resetting the weight down to a hang.
Thoughts?