lactate threshold question

mongoose

Can anyone tell me what it means to ride aerobically, and not to exceed your aerobic, or lactate threshold.

dhk

At an aerobic pace, your cardiovascular system is supplying all the blood oxygen needed to the muscles for efficient production of energy. If you're trained, and have sufficient carb intake, you should be able to ride all day at an aerobic pace.

When you exceed this pace, somewhere around 85% of your maximum HR or VO2 max, the anaerobic energy system has to kick in. This energy system has a limited-life related to the build up lactic acid in the blood. Your legs will start burning after a short time, (maybe one minute) and then power output will suffer which will force you to slow down, fall back in the pack and recover.

That's a basic answer..but about all I know. Lots more science if you want to search and read about it.

Dan

mongoose

Thanks for your reply, would i be right in saying that you are producing more latic acid in your muscle, than your system can carry away?

dhk

I think that's a correct statement. Believe the muscles always produce a small amount of lactic acid, but at the threshold power level it starts increasing on a steep slope upwards. One formal test procedure discussed in Ed Burke's book Serious Cycling has the subject work at increasing VO2 levels while taking blood samples every few minutes. The lactic levels are then plotted vs time and VO2 %. The threshold point is based on a blood concentration of either 1 mmol/l or 4 mmol/l, or the change in slope of the graph.

The experts here can probably provide a lot more details about test procedures. An estimate of lactate threshold is often taken as 85% of max HR, but this seems on the low side for me. The Karvonen method calculates 88%, which seems right about on the money for me based on the HR number I see on long hard hill climbs.

In the book Lance Armstrong Performance Program, he states his LT is 178, and his max HR is 201. That's a LT of 88.6%. He also lists that his average time trial HR is 188-192, and average for his 4-6 hour endurance rides is 124-128.

Dan

2LAP

Thats spot on, LT occurs when more lactate is being produced than can be removed from circulation.

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dhk

2Lap: Can you please comment about determining LT without a lab test procedure. A local trainer who talked to our club just said to always use 85% of our max HR. But, as I mentioned above, the Karvonen method estimates my LT at 88% of max HR, or 163 bpm out of 184 max. This figure seems to be what I can hold on a long hill for 10 minutes on a good day.

Do you think these figures would fairly represent the LT zone points for me, or is a lab test really required for this precision?

Dan

hugefeet

Unfortunately there is no definite way of determinging a persons lactate threshold accurately without blood testing at increments corresponding to exercise intensity. Just keep in mind the only effective way to increase lactate threshold levels is by interval training with at least 55-60(unfit) to 90% max HR or 40-50(unfit) to 85% of V02max. With training at these intensities you will see the most physiological benefits ie. easiest way to increase V02max and OBLA or LT.

HK, Human-what?

2LAP

Unfortunately you need to visit a lab as hugefeet pointed out. As well as the training suggested by huge feet, intervals at TT pace of 2 to 3 of 15 to 30 minutes will help and are commonly used.

Check out the training forum for more sessions (lots of LT stuff on there).

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ric_stern/RST

To clarify: LT is actually quite a low intensity, and is defined in a lab as a workload that elicits a 1 mmol/L increase in lactate over exercise baseline levels or at a fixed 2.5 mmol/L workload. Thus, this intensity is somewhat below TT power (i.e. what you can sustain for an ~1-hr), approximately, 15 - 20 % less power.

At LT power you should be able to sustain this intensity from >1-hr to several + hours.

Additionally, LT is *never* defined as a HR, either as a single point or as a range. HR can vary for a multitude of factors (e.g., heat, humidity, altitude, fatigue, food, etc.). LT is only ever the workload that elicits the increase in lactate, and as such is measured in power (cycling) or velocity (running).

Ric

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dhk

2Lap/Ric: Thanks for the responses. Helps bring those big HRM numbers I see when I'm working hard into perspective!

Dan

tafi

A good method for gaining an estimate of LT heart rate is to work based on average heart rates over a time trial (which is usually done as a sustained hard effort).
Depending on the length of the time trial and whether you do it in training or as a competition, the average heart rate will be a proportion of yur lactate threshold heart rate.
eg: a 40km time trial is 100% of LTHR if it is a race and ~97% of LTHR if it is in training. I don't know quite how accurate it is but it works as a guide for setting training intensities. As you get fitter of course your LT will be at higher intensities so you will need to retest every 6 months or year.