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 VLa_max and VO₂max to predict your two lactate thresholds – which we use to determine training zones – and your Fat_max, or the intensity at which...

As we have discussed at length in previous blogs, and in our courses, carbohydrates and fats provide the energy to fuel metabolism during prolonged, endurance exercise (3). The carbohydrate energy we have stored in our muscles and liver as glycogen is limited, and can become depleted to low concentrations during long-duration exercises like Ironman triathlon (1, 6). In contrast, our fat energy stores, whilst metabolised more slowly, are effectively limitless in the context of exercise. For example, given that 1 g of fat provides ~9.75 kcal of energy (4), it can be estimated that a lean 70-kg individual with 10% body fat has ~68,250 kcal of endogenous fat energy. Theoretically at least, this is enough energy to complete more than six full-distance Ironman triathlons (5).

Accordingly, exercise physiologists have conducted huge amounts of research into the factors that influence the rates at which we metabolise fats and carbohydrates during exercise. This research has been particularly...