Reactive Training Systems

I'll have a crack at it as I think I'm starting to see something.

Energy cannot be destroyed or created, only converted from one for to another, now when we deadlift we are tranfering potential energy in us, into kinetic energy as we move it into potential energy again as we hold it. Some energy will be "wasted" in heat, sound etc but this is the gist.

Now we drop the bar, potential energy is once again converted into kinetic energy and a whole lot of sound (a less useful form of kinetic energy), however what eric would seem to suggest is that some how, we have a larger portion of potential energy in our system this time round. Now, I'm not doubting it must be true but the basic physics of it actually doesn't make sense: without getting into formulas etc, we seem to have added some energy into the system from somewhere. We had to initially have the potential stored energy in us on the first rep equivalent to the force gravity would have acting on the bar at the height of lockout. Otherwise we wouldn't complete the lift, so the energy system goes us-kinetic-gravitational potential-kinetic-us/the bar. Yet somehow we are saying in that final state there's now more energy in the system... Where from?

I see what you mean Joe but there still can't be anymore energy added to the system as the whole thing kicked off with the chemical energy which must have been sufficient to transfer to gravitational potential at the top of the lift.

All I can think is that the increased mechanical energy after the initial rep is more accessible to the body, hence the faster rep.

Ok, its clicked. Nice sports science lesson, so on the second rep we have our replenished (almost) energy systems plus a potential energy left in the tank from our last effort=faster pull.

After some thought, I am going to agree partially but make the hypothesis that the majority of the speed increase is not due to stored mechanical energy but due to the unique conservative nature of the human nervous system.

The stretch reflex I beleive to be a good form of stored energy but once the lifter stands back up the reflex is lost since the muscles are somewhat lengthened in the standing position. With the argument that this reflex last for several seconds I will sound like a idiot for disagreeing with a an actual lab test but I have seen many poor conclusions from many tests. That being said consider a simple stretch like a sitting hamstring stretch, when you sit and reach and feel the stretch, the moment you relax do you bounce back, now stretch again, you don't bounce back noticably harder the next time.
As for energy being stored in the muscle other than the in the form of tension, it is not possible, the krebs cycle cannot work in the reverse. Meaning that lengthing a muscle does not create ATP, which is the only source of energy that can cause a muscle contraction. The potential energy that is in the rasied bar is converted to noise and heat in the muscles as the opposing muscles resist the decent.

I hypothesis that the real reason for the faster pull is due to the ramp up of the human nervous system. Like me, the nervous system is lazy. It does not instantly activate the maximum number of muscle fibers at its disposal. Instead it adds recruitment until the bar begins to move then adds more as we get to our sticking point, this enables us to "grind it out" a process which is always slow. I have no evidence to back this up but it makes a great deal of sense since your likely not getting stronger as you hit your sticking poin,, and the nervous system always fires at the same strength,meaning it doesn't fire harder just fires more neurons. What does this have to do with it getting easier on the second rep, well my theory is that the first rep the nervous system has to run all the way from its usual number of fibers up to the number of fibers it requires to lift the weight. On the second rep the nervous system starts at a higher number of fibers since it knows what is required now, and the process to get to the required number is quicker, thus the rep is quicker. The key to my argument is that the nervous system is very much like me. Not only lazy but also forgetful. It resets to its usual number of fibers in only a few seconds, since using excess muscle fibers is inefficent and takes alot of calories that the body does not want to give up. So after several seconds you return to the bar and the blast you got from the second rep is gone.

Also this argument does not apply after several sets, but this is mostly due to fatigue and should not be considered since the body is low on fuel and this point and regardless of recruitment it does not have the calories to use, thus the nervous system won't jump in a car without gas.(meaning it won't recruit muscles it can't afford to contract)

Finally, the extra recruitment of fibers during a grind is borrowed from a physiology study I read and not my hypothesis.

Ok sorry for the length, I hope this at least leads to some good thinking

-- Edited by Nick U on Tuesday 31st of March 2009 09:09:33 PM

-- Edited by Nick U on Tuesday 31st of March 2009 09:10:16 PM

Dano, yes that's what I was referring to. From what I have read, one study said the stretch reflex lasts up to 4 seconds. But subsequent studies failed to reproduce this result (most suggest around 2 seconds).

It doesn't matter anyway, because the stretch reflex has to be a mechanical stretch under load. When you pause on a bench press, you are still under load (muscles still holding tension). In the deadlift, if you let the bar fully rest on the floor, then you are not holding the muscular tension required to maintain a stretch reflex, thus it should dissapate even faster.

So, to me, it could last 2 seconds under ideal circumstances, but in a deadlift, it will be significantly less than that.

And I agree with you on the amount of times "CNS" is misrepresented.

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