Kenny Croxdale is the prime opponent of a quick descent:
What was unique about Tom [HARDMAN] was his style... He had the fastest descent or eccentric phase in the bench press that I ever saw. He would take the hand off, hold it for a second at full arms length, then almost let the bar free fall to his chest... I never saw any other record holder bench like that. He was the exact opposite of say Doug Young, who brought the bar down very, very slowly prior to the concentric phase. Mike MacDonald was more of a medium descent....controlled at a medium pace...then BANG!
Croxdale on how equipment changes the equation:
Hardman's style is an exception to the rule. The problem in dropping the bar that fast to the chest is the reversal force needed to change it from an eccentric to a concentric movement. As I have posted before, research of novice/intermeditate benchers vs elite lifters was done (Dr Tom McLaughlin, PhD Biomechanics). The research showed the reversal force needed was 49% more for novice/intermediate lifters vs 12% for elite lifters. As an example, in bench pressing 300 lbs a novice/intermediate lifter would need a reversal force of 447 lbs vs 336 lbs for an elite lifter who lowered the bar slower. Thus, by letting the bar drop that fast, the impact force of the bar is magnified beyond it true weight. To eliminate the reversal force needed in dropping the bar that quickly, one would need to let the bar sit on the chest for a few seconds. The problem with that the longer it sits the less of the stretch reflex one has. Research show that 20% more power can be generated with the stretch reflex compared to pushing/pulling a weight from a dead stop. That is why you can bench press more with a touch and go than from a dead stop. So, letting the bar drop that fast is NOT the best method of bench pressing more weight. Haden is a freak in this regard. Doug Young's style is one almost every bench presser should emulate. Young decent was slow and controlled. Thus, less reversal force was needed to push the bar up... For the majority of bench pressers, letting the eccentric speed of the bar accelerate (fall like a rock) will nail you to the bench. It a bad idea. There a are some lifters who may do well with it...but only a handfull at best.
However, while the supershirts may allow one to lower the bar a bit faster, the question becomes how much faster before the impact force magnifies it to a point beyond your reversal stength?.. Super shirts are super tight off the bottom of the chest. More force is needed to drive the weight down. Thus, more eccentric acceleration does help. However, even with super shirts on there is some point of diminishing return when it comes to eccentric speed.
While benching in a super shirt does alter the laws of physics, it does NOT eliminate it completely.
One of the keys is how fast the bar decents. When using a heavy load in the bench press training, the bar decent should be slow until about 2 inches from the chest. At about 2 inches off the chest, you allow the bar to drop. This method of benching minimizes the impact force while evoking the stretch reflex. When lighter loads are used in training a much faster eccentric decent can be performed.
Others think Croxdale may be looking at an incomplete picture:
What you want to do is, so to speak, find a speed that allows you to minimize the impact force and allows you to evoke the stretch reflex.
Kenny, I think the idea of fast vs. slow eccentric is more complex than you are presenting. I agree that a greater amount of force is needed to reverse the movement, that is a given. That said, there could be other factors. For example, does the slow negative fatigue the involved musculature to a greater degree than a fast negative thus negating the max force production difference for the reversal (in terms of leaving sufficient force production capability for the press)? Also, keep in mind that when benching with pause you only need to stop the barbell on the chest, you are not immediately reversing direction in terms of having to accelerate in the opposite direction once the barbell is stopped. I am not necessarily arguing your point, just saying there could be more to the story.
Although when bar is accelerated, it does weigh more than the actual weight on the bar, but respectivley the muscle has more potiental for stretch reflex and using its elastic component.
Using the simplest application (and an very INEXACT one I might add) of physics you have only demonstrated the obivous which is that it requires more force to stop the movement on one's chest if the bar is dropped quickly. It is VERY POOR SCIENCE to conclude that the above statement is definitite proof that lowering the bar quickly to one's chest is a bad idea when trying to press maximal loads. Now, that could very well be the case but due to the reasons I proposed and many others it is quite possibly not the case as well.
So one has to wonder, what causes the most fatigue, stopping a big force very quickly (the weight/force is greater because of speed), or stopping a not so large force over a longer period of time. I would think the later would cause less fatique and have more of a stretch reflex benefit as long as the weight is controled and in groove.