Lactate Test #2: What happened to aerobic capacity?

On May 21st, I did my second lactate capacity test of the season. I planned on both an aerobic and anaerobic capacity check during the test. But the aerobic part of the test was too long. It likely caused a bit of glycogen depletion.

Depletion would have compromised the results of the anaerobic part of the test. To minimize interference between the two tests, I did the anaerobic part two days later. I may do that from now on.

The combined test had mixed results. By both heart rate and pace, my aerobic capacity appears to have weakened. (This is shown by the blue line being above and left of the red line) My anaerobic capacity appears to be the same as in early April (14.5 versus 14.6).

A chart of the second lactate test compared to the first
Lactate Test #2: What happened to aerobic capacity? The blue line being above and left of the red line suggests that aerobic capacity has declined? However, anaerobic capacity is the same, but via a shorter interval.

Isn’t that bad?

At first glance, it appears that the first phase of this year’s training cycle hasn’t gone as planned. The results seem worse than the first test.

But I suspect that my aerobic capacity is still the same or stronger due to the following factors:

  • The anaerobic result came from a 60″ AFAP interval rather than a 90″ interval (which is what I used in early April). I produced the same lactate in 33% less time. That being the case, I suspect that my anaerobic capacity has increased since early April. If true, then my aerobic capacity will appear weaker. (The two capacities always present relative to one another; not in absolute measures.)
  • I can now jog at less than 60% of maximum heart rate. When I first started training, I couldn’t jog at less than 75%. Over the past few years, my heart rate during easy runs has steadily fallen. At less than 60% of maximum, it’s lower than ever.
  • I’m training at a record high volume than I have in the past, and I’m recovering well. That suggests a greater work capacity which should support a higher aerobic capacity.

What training led to this?

Here’s a breakdown of the training that I’ve done in the first seven weeks of this year’s program:

  • Training Focus: max strength, hill sprints, fasted sessions, super easy volume
  • Intensity: 98.7% <= aerobic threshold heart rate (AeT HR); ~74% <= 80% of AeT HR.
  • Specificity: ~87% of training time was running, ski mountaineering, hiking, and roller skiing.
Charts of total trianing time broken down by intensity and mode

How does this influence the next training phase?

I suspect that my aerobic capacity is stable. But I’d still like to see both aerobic and anaerobic capacities progress. I don’t want to wake up months from now and find out that I went down the wrong path.

To that end, I’m going to change my original plan in a few ways:

  • Slow down anaerobic development
    I’ve been doing AnC work twice a week, but that may be too much right now. I’m going to cut that back to once a week.
  • Increase the pace of aerobic capacity workouts
    My original plan was to postpone the faster AeC work for a little longer. But with lactate at ~2 mM between 160 and 170, that’s 10-20 beats lower than normal. By doing more work in the 160 range, my metabolic efficiency should improve.
  • Fall back on nose breathing as an in-session limiter
    Although I know that my current ~2 mM threshold is in the 160s, I want to make sure that I don’t exceed it. That could create a long-term problem. For AeC sessions, I’ll make sure to only breathe through my nose. Nose breathing provides great, real-time feedback on lactate levels. The limit of nose breathing usually corresponds with the aerobic threshold.
  • Do more roller skiing
    The first phase of this season was at the tail end of winter, so I still had a decent amount of volume on skis. Now that spring has sprung, ski days will be less and less common. To make up for the change, I’ll need to increase my time on roller skis, ideally one-third or more of total training time.
  • Do more run-hiking
    Most of my training so far has been running, either on flat or rolling terrain. I can feel my runs getting faster, but I can also feel steep terrain is less familiar. That may have been a factor in this test as well. I’m going to do more steep run-hiking so that I don’t lose that specificity.

The conflicting factor

It has always been part of my plan to start Local Muscular Endurance training now. Yuri Verkhoshansky’s LME work for distance runners should start stimulating some lactate shuttling. That should increase my speed in the short run, and reduce lactate levels in the long run. However, my lactate curve in the short run may worsen. We’ll see.