[Scott Johnston]

Danny:

More good questions on this topic. Let’s start with the first one you asked.

I’m doubtful it would be possible for one to maintain a lactate level of 4mMol/L for 50% of a marathon.  I’m speculating here because there is a dearth of info on this topic.  It might help us if we go back to first principles and examine what is happening metabolically to power the marathon.  To run at around 5min/mile speeds takes a lot of glucose or a high glycolytic flux because glycolysis is a faster way of regenerating ATP than is fat metabolism.  Remember that the main byproduct of glycolysis is pyruvate which if it hangs around in the cytosol converts to lactate.  Both pyruvate and lactate are high-energy fuels if they can be taken into the mitochondria and oxidized.   The bigger the aerobic capacity of the muscle fibers the more mitochondrial density and the greater capacity to take up that pyruvate and lactate and do something useful with it.  So, while these faster marathoners are producing a lot of lactate it is not accumulating in the cytosol of the cells and blood lactate levels remain fairly low because they have huge aerobic capacity (the big vacuum I refer to in the books).  Finding the balance of the fastest speed with the lowest lactate is the goal of any endurance racer in any distance race. That is why we use the types of workouts I mentioned before.  It should be obvious that someone who can run 3x5km with a lactate level of around 2.5mMol/L is going to be able to sustain that pace for longer than someone producing 3mMol/L.   Not running out of our quite limited glycogen stores before the final miles of a marathon is one of the biggest issues facing any marathoner.

Only someone who paced themselves perfectly would have the glycolytic reserves to run fast enough to produce more than 4mMol/L at the end of a marathon since glycogen stores will be very low. I think this would be especially true for the last 10% of the marathon since we could be talking 15 minutes for a 2:30 runner.  Fifteen minutes at say 5-6mMol/L after running 23 miles at 5:15min/mile would seem to me to be superhuman.  I once lactate tested some top skiers during a 3-hour Zone 2 workout where I asked them to finish with 5 minutes as hard as they could go.  What I saw were lactate levels of 2 and below. The only explanation that I could think of was that their glycogen stores were so depleted that they could not produce higher speeds that would have produced higher lactates.

I sometimes employ a very challenging interval workout for both skiers and runners that will cause lactate levels to reach into the 5-8mMol/L range after the 5th and 10th repetition.  To check their ability to sprint at the end of the 10th repetition I will have them do an 800m max effort immediately after we get the lactate reading from #10.  When they are not yet in shape I will see low lactates and slow times for this 800 (their glycogen tank was nearly empty).  As their fitness improves I see the 800 time drop and the lactate levels climb.  This tells me that they can conserve glycogen at faster speeds by using more fat. This enables them to have a strong kick at the finish.  A great demonstration of this in action was the finishing kick of Cole Hocker’s gold medal 1500 in the Paris Olympics this week.  He had to have conserved his glycogen stores to pull that off.

I’m far from an expert on the marathon or physiology. I am working with what I have personally observed and the little understanding I have of metabolism.  If you can find some conflicting information on lactate levels during marathon racing please share them here.

Your second question concerning heart rate:  I say forget max HR or % of maxHR as they are not relevant to these discussions.  What we do is to find the athlete’s individual aerobic and anaerobic thresholds through very simple testing explained here https://evokeendurance.com/our-latest-thinking-on-aerobic-assessment-for-the-mountain-athlete/

These tests will quite accurately and easily identify the athlete’s metabolic response to changes in intensity.  If we correlate this to HR we have a reasonable way to prescribe and control training intensity.  If you couple that with RPE you have a nice set of tools for controlling and monitoring intensity that will allow the athlete to learn and correlate HR to RPE under most conditions.  One problem with RPE alone is that you have no way of connecting that to the underlying metabolism.  So, you are just guessing about that all-important metabolic process that is fueling the work you are doing. The other more insidious problem of using RPE alone, especially for beginners with training is that they have no idea what “easy” feels like and tend to train too hard too often. This leads them into over-training.  I have had even high-level ultra runners come to me quite overtrained because they relied on RPE alone.  As with the above marathon lactate question it is, again,  just my observation of hundreds of athletes over several decades.

I’m not sure I have adequately answered you but thanks for the interesting questions.
Scott