I read somewhere that at about 90 minutes into a long run your body undergoes glycogen regenesis, and really kicks in to generate additional glycogen. Not being a chemist, biologist, or any other type of -ist, I don't know if this is true, but I think i read it in something that Hal Higdon wrote, and him being the running guru guy, i'm inclined to believe it. The "Second wind" phenomenon can also be an onset of "runner's high" and I know i've definately felt this. It's part of the reason that I love to do my hour+ long runs, knowing that towards the end, i'll be giddy and unable to stop smiling.

I know what you are saying about runners high, but I am talking about actually having, in my opinion, more energy available. I am using one of Hal Higdon's training programs for my upcoming marathon I will have to look for that reference on his site.

Jim

I love being wrong because then I know I learned something today.

Jim, I'm going to take a WAG about it. Remember, I'm just guessing...here goes.

A relatively mildly acidic cellular state actually favors oxygen transport from the blood to the interstitial spaces and across the cell membrane, and therefore oxygen is more available to the mitochondria to "do their thing" called the Kreb's Cycle. The Kreb's Cycle is a very aerodynamic bicycle made up of Kallikrien, Ribonucleic acid, Eosinophils, and Bat spit....OK, I just threw that in there to make sure you know I'm just making up this answer, I haven't fully researched it, but I wouldn't be surprised if my answer is actually correct.

When you first begin exercising, you do indeed increase the temperature in the muscles...thus the term Warm-up. Increased temperatures shift the oxyhemoglobin curve to the right, meaning, oxygen is "unloaded" to the tissues more easily. Increasing acidity also results in the same rightward shift characteristics in the oxyhemoglobin curve. Guess what? So does an increase in CO2 (which shouldn't be surprising, because CO2 can be considered to be an acid, as CO2 forms carbonic acid using carbonic anhydrase as the enzyme to speed this reaction along.)

Anyway, I'm going to guess that some of the other exercise-induced changes that begin to occur to assist one in continuing to exercise (such as gluconeogenesis, increased cardiac output, lubrication of the muscle sheaths, dilation of the arterioles/capillary beds, etc.) start to all cuminate at a point of near-maximum efficiency...this is a point where you actually are starting to get some increasing acid buildup at the cellular level. Probably mostly lactic acid. As long as it is a mildly acidic state, it is NOT bad for your muscle function, and it's very good for oxygen transport.

So, you have all these systems peaking at about the same time, and majically, you experience the "second wind". It's interesting that this second wind really exists, but, what is more interesting to me is that the second wind is also a signal that things are going to start coming apart soon...it's a sign that you've reached maximal efficiency, and unless you do something to preserve this effort level, you can step over the cliff and get into decreased performance levels pretty quickly...or, you can ease up just a hair, and the second wind hangs around a LOT longer. A LOT longer.

Or, by "second wind", are you referring to something associated with eating legumes, cabbage, and chili?

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Quid quid latine dictum sit altum videtur
(That which is said in Latin sounds profound)

All true, but this sounds a lot more like "being warmed up" rather than a second wind.

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Some postulate that this is due to the effects of the 'lactate shuttle'.

When an effort is sustained at a level where blood lactate starts to rapidly rise (i.e. lactate threshold), lactate is 'shuttled' in the bloodstream to other tissues for use as fuel, lactate consumption increases, blood lactate starts to level off at some elevated level, and some relief is felt as lactic acid levels are held relatively constant due to lactate consumption 'catching up' to production.

But it isn't the lactate per se which causes the pain, its the H+ which is generated along with it. How would shuttling of lactate change one's perceived exertion?

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Good question. Not sure I'm sold on the relationship between the 'lactate shuttle' and a second wind either. Figured it was worth offering up though.

Check this out:

http://www.ncbi.nlm.nih.gov/...51&dopt=Abstract

Might have something to do with the observed delay in decrease of blood bicarbonate with the observed increase in blood lactate accumulation. Seems that lactic acid is initially buffered in the muscle cells and then neutralized in the blood by natural bicarbonate as lactate levels rise. Maybe it takes a while for all of this to reach steady state??? Maybe after a while we just tolerate the increased acidity better??? I don't know.

This is what I love about Slowtwitch, you ask a simple question, you get an answer I have to go back to school for. Just kidding, As the original poster I had hoped to contribute more to this thread but it has gone a little over my head. So I will sit back relax and learn.

However, in reply to Just Curious, I think that the "steady state" idea has a lot of merit I do notice less lactate burn during this time.

Jim

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Jim

**Note above poster works for a retailer selling bikes and related gear*

lactate reportedly causes pain, but, at what level? We all have lactate in our bloodstreams right now. Lactate doesn't equal pain, however, at some level, increasing lactate is associated with pain.

As I said before, this was a WAG, although we may be on to a kernel of truth...don't know for sure.

Do you guys get the same perception that I do...once that second wind has happened, you have to back off just a bit in order to keep it around? And if you don't back off just a bit, and end up crashing, you crash fairly hard? For me, it signals a point on an imaginary cliff that I have to step back from to make sure I don't slip over the edge. Of course, if it is the end of a race...you just keep pushing.

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Quid quid latine dictum sit altum videtur
(That which is said in Latin sounds profound)

I think it takes me an hour to warm up. Seriously, it seems to take forever now that I'm not 20 anymore.

As JHC pointed out, it's not the lactate that causes the burn and screws everything up, it's the hydrogen ions that are produced with the lactate during exercise (hence the term lactic acid).

If you look at getting a second wind from an 'energy or fuel availability' standpoint instead of a 'decreasing discomfort' standpoint, the lactate shuttle theory does kind of make sense as lactate can be used very rapidly and readily for fuel. (Much more so than blood glucose for example.)

Yes, back down just a notch, and keep going all day. Don't back down, and in a mile your done.

Jim

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Jim

**Note above poster works for a retailer selling bikes and related gear*