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Fitness Theory and Practice. CrossFit's rationale & foundations. Who is fit? What is fitness?

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Old 09-11-2005, 10:39 PM   #1
Eric Cimrhanzel
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I've been hearing from Grease The Groove (and other low-rep, high-weight, long rest training) advocates that it "gives your Central Nervous System a boost". Can someone explain to me what exactly that means? I'm talking from a physiological psychology perspective, what does this "boost" entail? What chemicals in the brain are activated when strength training like this? Does this allow more neurons to connect to one another, such as what happens whenever we learn something new?

I asked one of my nueroscience professors about this after a class last week, and he didn't have a clue what I was talking about when I said "boost to your Central Nervous System".

I don't even know how to search for this, so if someone has resources (not Power To The People. I've read that), especially scientific, that they could point to, that would be greatly appreciated.
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Old 09-11-2005, 11:30 PM   #2
Rene Renteria
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Hi. Good question. I've usually thought they were referring to motor unit recruitment. When trying to maximally activate a muscle, we don't necessarily cause all the motor units making up that muscle to fire. Training improves the amount of motor units recruited during the effort, thus increasing the maximal force applied independent of increases in the strength of the muscle itself.

Try looking up "exercise motor recruitment" in PubMed, which, for example, turns up abstracts like this: ct&list_uids=16129897&query_hl=1
Can J Appl Physiol. 2005 Jun;30(3):328-40. Related Articles, Links

Resistance training: cortical, spinal, and motor unit adaptations.

Griffin L, Cafarelli E.

Dept. of Kinesiology and Health Education, University of Texas, Austin, TX 78712, USA.

During the first few weeks of isometric resistance training there is an increase in maximal muscle force output that cannot be accounted for by muscle hypertrophy. Early on, researchers postulated the existence of neural adaptations to training primarily through the use of surface electromyographic recordings. More recent evidence also suggests that increased excitation may occur at the cortical levels following short-term resistance training. Alterations in synergistic activation and reductions in antagonist activation are neural factors that have been identified as changing during the early stages of resistance training which could contribute to maximal force generation. Neural adaptations that occur during the ramp-up phase of isometric contraction include decreases in motor unit recruitment thresholds, increased motor unit discharge rates, and increases in double discharges. An increase in the maximal rate of force development also occurs during the early stages of resistance training, but whether the neural mechanisms associated with the increase in the rate of rise are also associated with the increase in maximal force has not been elucidated. More work is needed to examine the integration of changes in cortical and spinal excitability with single motor unit firing patterns during this simple form of exercise before we can extend our understanding to different types of training.

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Old 09-12-2005, 06:05 AM   #3
Steve Shafley
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More practice of the proper technique leads to increases in the efficiency of the movement, allowing greater weight to be lifted.

There's also the entire "neuromagnitude" vs "neuroduration" thing: Basically when you miss a maximal lift, do you miss it because you can't generate a big enough neural impulse to do it, or because you can't maintain the impulse long enough to finish the lift? Some interesting, yet hard to read, stuff about this over at

If you are interested in practical ways to "prime" the CNS, you are going to have to go over to and do a search on it. CF puts great store into using certain exercises at certain times to keep a certain amount of tonus in the body before competition.

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Old 09-12-2005, 06:06 AM   #4
Russ Greene
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On a related note, I've tried to explain the basic idea behind the phosphate (ATP), glycolytic, and oxidative energy systems to biochem people and they didn't seem to have a clue what I was talking about. They seemed to just think in terms of aerobic or anerobic respiration. Do any of you science geniuses know why that could be? Do you guys use different words, or think about it in a different way?
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Old 09-12-2005, 07:32 AM   #5
Barry Cooper
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Vladimir Zatriorsky's book "Science and Practice of Strength Training" indirectly addesses some of these basic points, like how many muscle units get recruited matters, whether they are recruited at the same time or randomly, and how often they fire. Also, (if memory serves)the "faster" (lower threshold) muscle units tend to fire the most to begin with, then as they fatigue, the slower (higher threshold) fire more.

None of that affects the price of tea in China, though. As far as I can tell, no one knows with certainty even to this day exactly what produces muscle fatigue, other than of course persistent effort in an oxygen debt situation, which produces lactic acid, which messes the muscles up.

As far as the 3 stage adaption, that is from a specific theorist, I believe. One of the science guys will know who.

Being a pontificator, though, I would like to add that the bulk of scientists spend the bulk of their time studying elms, and oaks, and beeches, and birches, and wonder why their theoretical models differ. The unifying perspective is that of the forest itself, which is rarely if ever seen by professionals. Hence the black box.
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Old 09-12-2005, 11:53 AM   #6
Robert Wolf
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Unless you have a "science" type who is really into performance they are going to be completely ignorant as to these distinctions. This is somewhat the difference between talking to a "scientist" about a problem and an engineer. Both might be smart but scientists are largely interested in theory and data generation. Engineers are interested in results. Possibly a generalization but this is the basic idea.

With regards to the original question of what this training is doing to the CNS? The right amount is a "tonic" and is beneficial, too much is a chronic stressor and not beneficial. From a motor learnign perspective we have some interesting models that describe some things that might be occuring here but I think Steves explanation and links are as good as we can get at the moment.
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Old 09-14-2005, 12:39 AM   #7
Jason Erickson
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Eric -

I agree that the basic premise is to develop neuromuscular efficiency. "Boost the CNS" is really a misnomer. Your CNS isn't boosted, just better educated about how to best achieve the desire result. Here's an article I wrote that simplifies the whole concept:
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Old 09-14-2005, 06:11 AM   #8
Eric Cimrhanzel
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Very cool. Thanks everyone for your help and the links!
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