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QUESTION
I have been training a lot in zone 2 on my run. I was told that I should retest my LTHR every few months. If I am training right, should my LTHR go up or down? – Michael
ANSWER
By most standards, Zone 2 heart rate is at 80% to 90% of lactate threshold. Often overlooked, Zone 2 is actually a very important training zone. In fact, I have my East African runners training in that zone for a fair amount of their workload. We call them either “moderate” or “slow tempo” runs. These aren’t “junk” miles, but instead a critical part of every training cycle.
Over time, zone 2 training facilitates and enhances lactate uptake by developing slow twitch fibers with high mitochondrial counts and by producing higher amounts of enzymes and transporters that are responsible for gobbling up lactate (to use as an energy source) that is predominantly produced in the higher heart rate zones. The more efficient this system, the better the lactate uptake and the more efficient you become. Ultimately, what you want to accomplish with Zone 2 (and really all) training is a higher output (faster pace) at the same heart rate that you were running slower at before. For example, if before you could run an 8:00 minute mile at 150 bpm, you’ll want to be able to run a 8:00 minute mile at 145 bpm in the future. However, this is where it can get a bit confusing.
As you train, you become more efficient at using lactate as fuel, meaning that you can actually run at a higher heart rate and produce less excess lactate. Therefore, as you get fitter and do more zone 2 training, LTHR should be HIGHER than previously measured. What has happened is that you can now run at a higher intensity (increased heart rate) and uptake lactate more efficiently.
Simply, to be the best distance runner you can be, you want to have a LTHR at the highest percentage possible of your max heart rate. This is why great marathoners are great marathoners. They can run at a very higher percentage (say, 95%) of their max heart rate without going anaerobic (producing more lactate than their body can clear/use efficiently). What we see is that when athletes get fitter, their heart rate actually stays similar and what changes is the percent of that heart rate at which they can stay “aerobic.” Therefore, technically, your LTHR should actually go up with improved fitness. A bit confusing, but I hope it helps!
