Training FAQ: The definition of threshold

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Dear Chris,
How do you define “threshold”?
— Chris

Dear Chris,
Within the sport of cycling, we often use the word “threshold” to mean threshold power. This is also often referred to as functional threshold power (FTP), and frequently used synonymously with terms like anaerobic threshold power, lactate threshold power, and others. In very simple terms, threshold power is the highest power that an athlete can sustain without accumulating short-term fatigue.

But the answer to your question about the definition of threshold is much more complex than that. I reached out to my colleague and Fast Talk podcast co-host Coach Trevor Connor for help. As a physiologist with years of coaching experience, this is a question he’s heard many times before. Here’s what Coach Connor had to say:

This is an extremely complex question. When researching it, I found over 20 different definitions of “threshold” (FTP, MLSS, VT2, anaerobic threshold, and so on.) One way to define threshold is your maximal sustainable power for a given length of time. For example, you could have a five-minute, 20-minute, and one-hour threshold. This definition is relevant to racing because you could use that wattage to gauge an effort of a certain length of time.

However, I prefer to think of threshold as the point at which a true metabolic event takes place inside your body. That is why I like the term Maximal Lactate Steady State (MLSS). It is the highest power at which you can sustain steady lactate levels in your blood. Training above MLSS works our energy systems differently than training below it, making it an effective number for defining training zones and workouts. Keep in mind you’ll rarely race at MLSS. Most race efforts are harder. That said, our one-hour power, or FTP, tends to be very close to MLSS.

One last thing to note. While there can be an unlimited number of time-based thresholds, when we talk about physiological thresholds there are only two. Besides anaerobic threshold, there is something called aerobic threshold, which is around 85 percent of MLSS.