What factors contribute to slowdown in race pace beyond HM (or roughly anaerobic threshold pace)

It's not a cut off point. The longer you race, the lower the lactate level because lactate is converted from glycogen and glucose, it is actually fermented glucose that goes on to be converted in to ATP as usable energy, so it has to be rationed in a long run.

Let me rephrase the question...

At distances run faster than anaerobic threshold, the accumulation of lactate is the primary limiting factor. Correct? Say your maximum lactate tolerance is 10 mmol (just a hypothetical figure, no idea what it typically is), the pace you can hold for mile/5k/10k/HM is whatever brings you to that lactate level by the end of the race.

But for distances run slower than anaerobic threshold, you never come close to that lactate limit. So what is the pace-limiting factor?

You already mentioned it...fuel supply and running economy at those speeds.

dfgdfhfhd wrote:

You already mentioned it...fuel supply and running economy at those speeds.

I didn't mention running economy. I don't see how that applies.

Suppose I can run a half at anaerobic threshold but my fuel supply will last to 18 miles. Why can't I hold HM pace to 18 miles?

HM pace is not a good example. For elite athletes, their HM pace hovers right around their anaerobic threshold. Running out of fuel does not happen at any set point for everybody. You might be more correct if you used time rather than distance as a metric but nonetheless running economy is the variable that allows runners to hold on to a pace longer than others because they are using less energy to run at that speed.

It's hard to calculate; I am certain pounding from the accumulated mileage causes fatigue and muscle damage. Running is merely a series of triple jumps. Pounding is the only reasonable reason why one is sore a week or more after racing ten miles and longer.

Definitely diminishing carbohydrate fuel is a problem as time goes on. Dehydration can also be a factor; the reason that each individual needs to test personal fluid loss over time, and not just rely on some formula.

Sorry, that's not the question I'm asking.

I think I can phrase the question better like this: Why can't you run indefinitely at your anaerobic threshold until you run out of fuel?

As an example, a runner who can race the HM at anaerobic threshold pace can't hold that pace to 25k, but an athlete should have plenty of fuel stores to reach 25k. What is forcing him to slow down?

Hog wrote:

Definitely diminishing carbohydrate fuel is a problem as time goes on. Dehydration can also be a factor; the reason that each individual needs to test personal fluid loss over time, and not just rely on some formula.

Does the body sense the diminishing fuel stores and force a slowdown before actually crashing?

Another theory wrote:

It's hard to calculate; I am certain pounding from the accumulated mileage causes fatigue and muscle damage. Running is merely a series of triple jumps. Pounding is the only reasonable reason why one is sore a week or more after racing ten miles and longer.

This was my initial thought. Which would explain why weights and long runs would help in marathon training.

Fuel availability is certainly an issue but so is the rate at which that fuel can be converted to ATP.

Even the leanest of runners has enough fat mass to fuel a marathon if not longer, but the problem is that it takes much longer to convert fat to ATP than to convert glucose/glycogen to ATP.

Then we add in neuromuscular junction fatigue in that the nervous system tires (oversimplifying there).

Heat build up can be a factor as well depends on conditions.

Here's my uneducated guess.

LT pace is the fastest pace at which you can remove/use lactate at the same rate it is produced. That we know. But the body cannot sustain that level of lactate usage indefinitely. So if you are running at LT your capacity to remove lactate stays steady for about an hour, at which point your lactate clearance capacity will start to decrease. Why? I dunno. maybe because your body starts to add some fat fuel to the mix after an hour, slowing down the energy production and therefore lactate usage.

You’re viewing AnT as a precise tipping point which it isn’t.

Joe Montana wrote:

You’re viewing AnT as a precise tipping point which it isn’t.

In theory there is a precise pace at which lactate is production/consumption is produced, correct? Are you saying this isn't the case, or are you saying that pace for this tipping point changes as throughout the run?

I think your argument is solid, but it's your knowledge of the basic concept that is flawed which is why you're in a conundrum of questions.

LT pace is a pace that one can sustain in ideal conditions for one hour in an all out effort. Whether that is 5 miles or 14 miles it doesn't matter how far it took you to run all out for that hour. What ever distance you covered would equate to your average pace aka your LT pace.( Ex, Time/Distance = LT pace :60mins/15k=4 min per kilometer pace aka LT pace.)

How far this individual will go in this hour largely depends on their fitness, followed by a variety of other factors such as genes, running economy, body mass, body structure, or what ever other physiological advantage the individual has (ex: altitude training) that helps them perform.

I don't believe the process of lactate being reabsorbed is linear. Meaning, I don't believe the body can equally produce and reabsorb lactate at the same rate it's produced. I believe the body produces lactate at a rate faster than it can be reabsorbed. We train and run at LT paces so the body can adapt and learn to be more efficient in limiting lactate produced and more efficient in reabsorbtion. The body will develop 'metabolic acidosis' which causes a long list of issues starting with organ failure. This is why despite the body may have theoretical energy to go a hypothetical 18 miles in your example, the body would likely fail due to too much lactate in the blood before ever getting there.

Perhaps I'm wrong

I think the answer lies in your concept of LT pace. It's not a constant as most people think. Typically, a runners LT pace will drift to a slower pace as a run progresses, but most runners start LT runs below their LT current pace to compensate. For example, a 6:00 pace may be an 85% max HR effort for the first mile, but by mile 5 that same pace is now 91% effort. We end the run and call it a day.

If, however, you ran indefinitely at say 90% max HR (this is roughly where LT occurs in most people) you might be running 5:50 for mile 1, 5:55 for mile 2, 6:00 for mile 3 and so forth. Eventually your LT will be rather slow due to fatigue, energy, dehydration, etc.

Dors that shed some light on your question?

It has to be a combo of things, but the brain will sense when you have went too fast for too long for your fitness level.

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Lack Tate wrote:

I think the answer lies in your concept of LT pace. It's not a constant as most people think. Typically, a runners LT pace will drift to a slower pace as a run progresses, but most runners start LT runs below their LT current pace to compensate. For example, a 6:00 pace may be an 85% max HR effort for the first mile, but by mile 5 that same pace is now 91% effort. We end the run and call it a day.

If, however, you ran indefinitely at say 90% max HR (this is roughly where LT occurs in most people) you might be running 5:50 for mile 1, 5:55 for mile 2, 6:00 for mile 3 and so forth. Eventually your LT will be rather slow due to fatigue, energy, dehydration, etc.

Dors that shed some light on your question?

It literally does not work like you describe. Your LT does not change every mile you run. If your LT pace was 6:00/mile you reach your steady state lactate level after about 5 minutes and for the next 50-70 mins you can hold that pace without lactate accumulation.

The question is why after about 60 min, the lactate levels begin to rise again?

no. not correct. at speeds in excess of your anaerobic threshold the limiting factors are muscle biology (fast twitch / slow twitch), muscle recruitment, capillary density, haemoglobin levels, enzyme activity. at these speeds it is primarily about force development and efficiency of motion. lactate is not insignificant, but far from being of primary importance, at these speeds.

no. not correct. (a more usual figure is 4 mmol) discussions of this topic tend to get very confused because there are two lactate thresholds and they each have several names.

1) there is lactate in your blood all the time. even when you are asleep. when you start to exercise, there is a point at which lactate starts to accumulate in the blood at higher than background levels. this is called onset of blood lactate accumulation, or it is also called the aerobic threshold (AT). the running velocity at which this occurs is what many runners refer to as Tempo pace.

2) there is assumed to be a point at which lactate accumulation in the blood achieves a maximum. work by the French physiologist Veronique Billat suggests that it goes up to a level, then as exercise intensity increases the level drops slightly before going higher without having been observed to achieve an actual maximum. however, most people in the field refer to this first level before the drop as the maximum and most runners and coaches when they talk about a maximum are referring to this pre-drop level. this point is the anaerobic thereshold (ANT), it is also called the maximum lactate steady state.

the difference between these two thresholds is known as your aerobic difference (AD). below AT you are running 100% aerobically. in the AD you are running somewhat aerobically but as speed increases the proportion of anaerobic effort increases until you reach ANT where you are running 100% anaerobically. therefore, the point of your training is to do three things: move AT as high as you can. make AD as wide as you can. make ANT as high as you can.

if you move AT higher, you are, essentially, increasing the speed you can run without accumulating lactate. the lactate itself is not the point, lactate is only used as a marker for the point at which you start to exercise anaerobically. the real point is the proportion of your effort that is aerobic at this level.

as you widen your AD, you increase the speed at which you are running anaerobically. again, the lactate itself is not the point. lactate is just a marker we can measure to determine where the point lies. the point is that at that speed you are 100% anaerobic, so you want to defer that point as long as you can.

it's called fatigue. physiologists have studied this for the last fifty years or so and the following appear to be true statements about the current knowledge of fatigue:

1) although many factors that might contribute to it have been identified, no one knows what causes fatigue. there are, essentially, three main candidates and the answer will undoubtedly be a combination of one or more of:

a) it is caused by levels of some as yet undetermined chemical substance or compound.

b) it is caused by a physical limitation to the function of muscles.

c) it is caused by a mental or psychological limit of some kind.

2) since no one knows what causes it, attempts to define it have boiled down to, "a sudden inability to do that which was recently possible."

3) training tends to defer the point at which fatigue occurs, but cannot eliminate it entirely. even highly trained athletes suffer from fatigue, eventually. there is enough fat in a runner to fuel his effort for approximately two days but he will suffer fatigue long before then.

Cheers.