Lactate Threshold

A few weeks ago I had a Lactate Threshold Test done at on a treadmill. It was pretty cool and is proving to be very useful (see my previous post where Coach Ben was able to tell me which “zones” to stay in during the marathons). Well, this past Saturday I went back to Absolute Endurance and had the same test done but this time on a bike. As you can see from the graphs, my LTHR (or Lactate Threshold Heart Rate) is quite different between the cycling (~140 bpm) and running (~159 bpm). Why? Well… first let’s talk about what lactate threshold is.

What is Lactate Threshold

I’ll let Joe Friel explain:

As your body uses carbohydrate to create energy, it creates a by-product inside the working muscle cells called lactic acid. As the intensity of a workout increases this liquid begins to seep out of the muscle cell into the surrounding space and blood stream. In so doing it changes its composition by giving off hydrogen ions. It’s now called lactate. Despite its “bad boy” reputation, lactate is actually a beneficial substance for the body during exercise as it is used to create more energy so that exercise may continue. It’s the hydrogen that is the real bogey man. This is what causes the burning sensation in your muscles and the heavy breathing at high effort levels. Measuring lactate levels in the blood is a convenient way of estimating how much hydrogen is in the body. The more intense the workout, the greater the amount of lactate released into the blood — and the more hydrogen ions interfering with muscle contractions.

Lactate threshold is sometimes referred to as anaerobic threshold. While sports scientists may argue about the differences between these two terms, for athletes there is little reason for concern. Both are essentially the high intensity at which you begin to “red line.” On a perceived exertion scale of 1 (low) to 10 (high) you redline at about 7 or 8. Whatever your heart rate, power or pace is at this moment is your lactate threshold intensity. The higher this is as a percentage of your aerobic capacity the faster you will race, especially in steady-state events such as triathlons or endurance running races. It’s common with fit athletes for their lactate thresholds to fall in the range of 80 to 85 percent of their aerobic capacities.

If you are using heart rate to determine your training zones, your lactate threshold heart rate (LTHR) is your average heart rate for a one-hour race effort. This is unique to the sport, so your rowing, cross-country skiing, swimming, cycling and running LTHRs are likely to be different. And therefore your heart rate zones will also be unique to each sport.

How did they do it?

Well, a fellow named Alan Chud stood next to me on the bike and the treadmill and watched my heart rate, my speed (treadmill) or my watts (bike) and every time my heart rate made a significant jump upwards (5 beats per minute – ish) he would pin-prick my finger and use a Lactate Pro Portable Blood Lactate Analyzer to see how much lactate was in my blood at that moment.

The protocol for the test involved:

  • First, get my running or cycling effort up to a rate of exertion where my body is no longer flushing lactate from my blood effectively – and take a reading.
  • Then, drop my physical effort down to where my body is clearing lactate efficiently again – take a reading,
  • Then, slowly ramp my effort back up to the “threshold” where I stopped clearing lactate again – taking readings along the way.

This effectively shows the heart rate, speed or wattage of when my body stops clearing lactate from my blood in an efficient way.

From there, we are able to establish my Heart Rate Zones, which I now use for training and racing as a guide of which energy system I am utilizing at any given point in a workout. For instance, when Ben told me to start running the WDW Marathon in Zone 2 (letting cardiac creep take me into Zone 3 but out of Zone 4 until I hit the 20 mile mark) I knew he meant I should keep my heart rate above 109bpm but below 131bpm, letting it creep above 132bpm but below 149bpm after 20 miles. This ensured that I saved a lot of OOMF for the last part of the race when Ben told me to “push into Zone 4” – which means I would actually be close to or exceeding my Lactate Threshold of 158bpm.

Conversely, this morning I did an easy (unfed) bike ride on my ergotrainer that was aimed to be purely aerobic. That means “Zone 2” or a heart rate of 97-117bpm. Basically I just had to make sure that I stayed under 117bpm and I was a happy rider… at 6:30am… in the dark… trying not to wake up my girlfriend.

You don’t have to do a Lactate Threshold Test in a lab to get these zones but it does make it easier and more exact… and it is pretty darn interesting and cool.

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