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Lactate threshold question.

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Lactate threshold question.

Old 08-31-04, 11:52 PM
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Lactate threshold question.

Hi all. In reading my "Triathlete's Training Bible", I noticed that Mr. Friel says that an athlete typically can't sustain activity over their LT for more than 5 minutes. Humm. I WAS pretty sure my LT was around 174BPM (max of 195). However, I can certainly maintain much higher than that for longer than 5 minutes. In my 3 mile TT bike fitness tests, I usually kept at 189-190 for the 8:28 it took me to finish them.
I regularly do hills (also on the bike) or hard riding over 180 for 10 minues or more. I did a ride with an ex-pro cyclist turned triathlete (qualified for Kona) and averaged 179 beats over 1 hour (Yes, I hurt like the devil. No, he didn't break a sweat). (Yeah, I'm toning down the hard rides. Time for actual training. I recently got back to above my previous level after a long break due to injury, and the excitement's getting the better of me.)

Just wondering if he made a typo, or if I just have a high LT. Haven't yet tried the 30 minute TT with the last 20min avg. HR being the LT, but plan on it this week.

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Old 09-01-04, 12:04 AM
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your LT isn't 174 bpm. It's higher.
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Old 09-01-04, 04:32 AM
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LT is not a function of heart rate, there is a rough corrolation but its not in its self reliable. It is maximum rate that the lactate cycle can function, thus keeping the blood lactate level from rising rapidly.(though there are accurate ways of estimating LT without blood samples)
Here is a moderately detailed explanation of the lactate cycle.
Remember that for your muscles to contract and propel you forward as you move along, your muscles require energy (how's that for an easy opener?). One of the key energy-producing processes inside your muscle cells is called oxygen-independent glycolysis.

During oxygen-independent glycolysis (the word glycolysis literally means the 'breaking' of glucose), glucose molecules are broken down inside the muscle cells; for each molecule of glucose degraded, two molecules of lactic acid are produced (lactic acid consists of a proton and our good friend lactate). This breakdown of glucose to lactic acid produces a fair amount of energy for contractions, and no oxygen is needed or utilized in the process.

Fatigue and feedback
As is the case with most cellular processes, feedback mechanisms can come into play. Specifically, if large quantities of lactate build up within a muscle cell, glycolysis is inhibited and the muscle fibre fatigues (the fatigue is not caused by lactate ions, however, but by the protons associated with them).

This fatigue can be prevented in two ways. A muscle cell can funnel lactate into 'oxidative phosphorylation', an oxygen-dependent process which breaks down the lactate and creates a substantial amount of usable energy.

Alternatively, the cell can dump lactate into its surroundings, pushing it out through its cell membrane and letting the lactate fend for itself in the cruel world of tissue fluids and capillary blood.

That 'push', however, is dependent on the presence of 'monocarboxylate transporters' (MCTs) which reside in the membranes of the muscle cells. These transporters actually 'grab' lactate and move it through the protein-lipid membrane grid, allowing lactate to escape. Without the transporters, lactate movement would proceed at a considerably slower pace.

The MCTs are like lactate doors, and scientists have discovered that the doors can function in a 'two-way' manner. When lactate levels are high within a muscle cell, MCTs can thrust a good portion of that lactate outside the cell. On the other hand, when lactate levels are soaring on the exterior, MCTs can bring the lactate inward. At this point in time, it's not exactly clear whether a single type of MCT can be both inward- and outward-directed, or whether different MCTs are needed for these opposing movements.

How the muscle fibres cooperate
At any rate, the MCTs' propensities to move lactate lead to some very interesting phenomena. For one thing, MCTs allow muscle cells to 'communicate' with each other, with lactate being the 'text' of the conversation. For example, your quadriceps muscles in your thighs are often a mix of 'fast-twitch' and 'slow-twitch' muscle cells. When you run, cycle, or swim at a hard pace, the fast-twitch fibres may begin emitting lactate at high rates (fast twitchers tend to have a high glycolytic capacity and thus can produce a lot of lactate, but they're not set up very well for oxidative phosphorylation, and so instead of breaking down lactate they tend to get rid of it). The neighbouring slow-twitch fibers may then begin plucking this lactate out of the muscle fluids. It all works out very nicely; the fast-twitchers can't use the lactate, so they give it to their neighbours, the slow-twitchers, who greedily break it down for energy.

What if the quads contain only slow-twitch fibres? That's no problem, because some of the slow fibres will be working harder than others (in any particular muscle, there can be great variation in force production between cells), and the intense toilers can spill their lactate to the more easygoing cells (slow-twitch fibres can produce lactate, in spite of their 'slowness').

If the quads are completely fast-twitch, things get more interesting. There will be lots of cells belching out lactate, but there won't be any cells standing by within the muscle with a high lactate-pick-up capacity (fast-twitchers are very poor at picking up lactate, for good reason; if they hold on to too much of the stuff, glycolysis will shut down). This is one reason why fast-twitch muscle fibres are not good for the long haul; by getting rid of lactate, they are throwing away a huge reservoir of useful energy. The lactate they give off usually ends up being used for energy by some other tissues in the body.
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Old 09-01-04, 07:00 AM
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you just need an LT test. it isn't automatically 90% of your max. you are better trained, so naturally your max stays the same and your LT increases.
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Old 09-01-04, 08:40 AM
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Do a search on LT. Koffee Brown has done an awesome write up on LT and will answer many questions.
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