The everyday language of training
Two athletes train at 250 W. One is working below LT2, the other above it. The difference isn't in the number. It's in how their body responds.
Talking about thresholds is talking about the everyday language of training.
They show up in exercise tests, in the planning of training zones, and in many of the decisions a coach has to make.
But there is an idea that often goes unnoticed.
Most people read thresholds as if they were an exact border. A point that splits training into two clearly separate parts.
The physiological reality is more complex.
The changes happening in the body don't appear instantly. They develop progressively, as multiple systems start to shift their behaviour at the same time.
NoteUnderstanding that difference changes how you interpret training.
What is a physiological threshold, really?
A physiological threshold isn't a switch that flips on or off.
It marks a range of intensities where certain physiological processes begin to change their behaviour in a noticeable way.
That is why we speak of LT1, LT2 or ventilatory thresholds. They all try to identify moments where the physiological balance starts to shift.
Not because one thing happens before and a completely different thing happens after. But because the dominance of certain mechanisms starts to move.
Why LT1 and LT2 aren't a border
It is tempting to think there is an exact line. 175 W. 4:05/km. 165 bpm. And to assume everything below it is aerobic and everything above is not.
But physiology doesn't work in borders.
As intensity rises, lactate production, ventilation, muscle recruitment, autonomic nervous system activity and energy cost all change at the same time.
All of these processes evolve continuously. Thresholds simply help describe where those changes start to become more visible.
That's why thresholds are a tool for interpreting physiology, not an exact boundary between two states.
This doesn't mean thresholds don't exist or aren't useful. It means they should be interpreted as physiological references, not as absolute limits.
What is actually happening inside the body
Lactate doesn't suddenly appear when you cross LT1. It is produced continuously.
What changes is the balance between production and clearance.
The same is true for heart rate, ventilation and metabolism.
NoteThresholds represent a progressive change in physiological balance, not an instant switch in how the body works.
The mistake of training to the millimetre
Many athletes worry when a session planned at 170 bpm ends up at 172. Or when a test sets LT1 at 245 W and they train at 250 W.
But thresholds are not an absolute number. They are a reference for interpreting the physiological response.
Reading them well requires understanding the athlete's state, the context and the goal of the session.
Context moves the thresholds
Thresholds can shift depending on many factors:
- Temperature
- Altitude
- Accumulated fatigue
- Hydration
- Sleep
- Training status
- Stress
That's why the same threshold can represent a different physiological response depending on context.
The same intensity can mean different physiological responses depending on the moment of the season.
How they should be interpreted
The value of thresholds is not in slicing training into rigid zones. It is in understanding how the body responds.
Finding a number is only the starting point.
NoteThe real goal is to interpret what that number means so you can make better training decisions.
Key takeaways
- Physiological thresholds are not rigid borders.
- LT1 and LT2 represent progressive changes in the body.
- Physiology changes continuously.
- Context modifies the physiological response.
- Interpreting a threshold matters more than memorising its value.
Thresholds don't separate two different ways of functioning. They help us interpret how physiology evolves as intensity changes.
