The Endure IQ Metabolic Calculator

Jun 03, 2024

I talk a lot about physiological profiling, and how getting tested in an exercise physiology laboratory can be really helpful for refining your training. However, I also know that many athletes do not have access to exercise physiology labs for this testing.

Accordingly, I’ve put together a couple of calculators on the Endure IQ website that you can use to get decent estimates of things like intensity thresholds using easy-to-access field test data.

In this section we are going to talk about the metabolic calculator. I’ll walk you through how to perform the field tests to get the necessary data. But we also include calculators for critical swim speed, functional thresholds power, and critical running speed.

#1: The metabolic calculator

Our first calculator, which you can find here, uses field test estimates of your VLamax and V̇O2max to predict your two lactate thresholds – which we use to determine training zones – and your Fatmax, or the intensity at which your highest rate of fat oxidation occurs. VLamax is the fastest rate at which you accumulate lactate in your blood, which is a measure of your capacity for rapid carbohydrate breakdown, and VO2max refers to the maximum rate at which you can consume oxygen, which is a cornerstone measure of aerobic fitness. These calculations used the principles outlined the great physiologists Mader and Heck (1986), "A Theory of the Metabolic Origin of 'Anaerobic Threshold'". Note the relationship between, VLamax, maximum aerobic power/VO2max and fat combustion/thresholds. It’s a fine balance, and higher VLamax values are generally associated with lower threshold and worse fat metabolism. For longer course triathlon, it’s important to choose when in the season your VLamax is at its highest. A high VLamax around racing most likely isn’t that advantageous. Lets take a look at how to perform the tests to get the necessary data for the metabolic calculator.

Field test estimate of VLamax

To estimate your VLamax, you need to measure blood lactate concentrations before and during recovery following a 15-s all-out sprint effort. The 15-s sprint effort is used to maximally stimulate lactate production, and you measure blood lactate concentrations during recovery to find the peak blood lactate concentration. Sometimes this will occur one-minute post-sprint, and sometimes this will occur five-minutes post-sprint. We find this test easiest to do on a stationary bike, as you are not moving, which makes things easier for whoever is taking the blood samples!

Here’s your protocol:

  1. Measure the resting blood lactate concentrations. Clean the skin with an alcohol wipe, prick the skin using a lancet, wipe away the first few drops of blood using clean gauze, and then analyse a small sample using your analyser.
  2. Prepare your lancet, analyser, and gauze for post-exercise samples.
  3. After a short lead-in, sprint as fast as you can for 15 seconds. Every pedal stroke should be at maximum effort.
  4. Measure the blood lactate concentration immediately after the sprint finishes.
  5. Measure the blood lactate concentration again after 1 and 3 minutes.
  6. Keep measuring the blood lactate concentration every two minutes until you are sure you are past the peak concentration – that is, until blood lactate concentrations are clearly on their way down.
  7. Make sure to complete a cool down.

Field test estimate of V̇O2max

Our field test estimate of V̇O2max is specific to cycling. Our field test involves you to perform a 5-min time trial, where the goal is to complete as much work as possible in the five minutes. The performance measure is your average power output over the five minutes. We also need your body mass in kilograms to generate our estimate of V̇O2max.

If you have never done a 5-min maximum effort before, it’s probably a good idea to have a go at one before your test – in research we use the term ‘familiarisation’ to describe this process. That’s just so you are less likely to come out of the traps too hard, or leave power out there.

Here’s your protocol:

  1. Measure your body mass in kilograms.
  2. Perform a warm-up. This should have you ready for action, but not fatigue you. I recommend no more than ~15-20 minutes. Over the first 10 minutes, build up from a very low power to something of a more moderate intensity. I then like to perform a series of ~10-20 second openers with quick cadence, with ~40-50 seconds of easy spinning between.
  3. Complete the 5-minute time trial. This is hard! Leave nothing out there. Focus on your cadence and consider blinding yourself to real-time power output.
  4. Make sure to complete a cool down afterwards.
  5. Extract your average power over the five minutes. Use average power, not normalised power.

Once you have these data head over to the Endure IQ calculator and enter those values to get your fat max, and thresholds.



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