Lactate Testing by Dr Jon Baker
Measuring Performance
In modern cycling, the measurement of power has become the norm. The power output we can maintain for a given time provides an objective measure of our performance.
It's fair to assume that your training is working when your power increases. However, we don't know exactly "what" changed physiology that led to an improvement in our performance.
Our muscles produce the energy for exercise and are where considerable fatigue originates – a fair place to begin our search for answers.
Lactate (and hydrogen ions)
Often, cyclists say their muscles are full of "lactic acid" when they're working hard on the bike. However, lactic acid is broken down almost immediately into two smaller compounds: "lactate" and "hydrogen ions".
What we "feel" is acidosis caused by the accumulation of these hydrogen ions in our muscles and blood – if you experience this during your long endurance rides, you're going too hard!
Lactate is a by-product of carbohydrate metabolism. Measuring lactate in the blood provides a unique insight into your fuel utilisation and, by proxy, the level of acidosis (and fatigue) occurring within your working muscles.
"Understanding how much carbohydrate and fat we're using at a given power output is beneficial, as it can help inform pacing and fuelling strategies during training and events."
Fuel Utilisation, Efficiency, and Endurance
Understanding how much carbohydrate and fat we're using at a given power output is beneficial, as it can help inform pacing and fuelling strategies during training and events.
We can also use it to evaluate your training. For example, an effective block of (Zone 2) endurance training should elicit two positive effects:
1. A reduction in blood lactate concentration at a given power output – indicates an increase in fat metabolism and less reliance on carbohydrates. We've become a more efficient endurance athlete.
2. Our endurance training "ceiling" is raised, whereby we can maintain higher power outputs without accumulating hydrogen ions that cause significant fatigue. We've become a more powerful endurance athlete.
Let's talk about thresholds
We can identify two distinct physiological thresholds that should define your training zones and determine the optimal power output for endurance and interval training.
Endurance training: When exercise intensity increases to a level where the primary fuel shifts (from fats) to carbohydrates, so does lactate production. When lactate production exceeds the removal rate, it accumulates in our muscles and blood, signalling we've reached the first lactate threshold (LT1). This is the upper limit for our endurance training.
Tempo training: We can tolerate exercise intensities slightly above the first lactate threshold for some time, often a few hours. However, higher carbohydrate oxidation rates lead to higher acidosis and increased fatigue. Without adequate recovery time, this may affect the quality of subsequent training sessions.
The upper limit of elevated but stable blood lactate concentration defines the second lactate threshold (LT2). This is an estimate of the actual physiological "maximal-steady state" and is closely related to the (often overestimated) "functional threshold power" (FTP).
Interval training: Above LT2 (and FTP), is where we typically perform our interval training sessions. Here lactate production is so high that it outstrips the body's ability to remove it. As a result, lactate and hydrogen ions rapidly accumulate in the muscle and blood, and exercise soon becomes intolerable.
