Your Lactate Threshold Isn't a Number. It's a Skill.

Most indoor cyclists know their FTP down to the watt. Fewer know what's actually happening at that intensity — or how to train it on purpose instead of by accident.

Lactate threshold (LT2, sometimes called your functional threshold) is the highest intensity you can hold where your body still clears lactate roughly as fast as it produces it. Push past it and lactate piles up, your legs go heavy, and the clock on your effort starts running fast. Ride right at it, and you can suffer productively for a long time. That's the whole game.

Why FTP isn't the same thing

FTP is a proxy — a number a test or an algorithm spits out to estimate the power you could theoretically hold for an hour. Threshold is the underlying physiology. You can have an accurate FTP number and still train threshold badly, because the workouts that raise it aren't "ride at FTP until you die." They're built around time spent hovering just below, at, and slightly above that line, teaching your body to buffer and clear lactate more efficiently.

That's a trainable skill, not a fixed ceiling. Riders who never do threshold work plateau at whatever their genetics handed them. Riders who train it deliberately move the line.

The indoor advantage

This is where a smart trainer actually beats the road. Threshold work depends on holding a narrow power band for extended stretches — 8 to 20 minutes at a time, sometimes longer. Outdoors, wind, traffic lights, and terrain constantly knock you off target. Indoors, with ERG mode or a controlled workout, you can hold 95–105% of FTP dead steady for the full interval. No coasting, no surging, no wasted watts.

If you're using VeloWorkout, this is exactly what structured threshold sessions are built for — the trainer holds the resistance, you hold the effort, and you get a clean picture afterward of how much time you actually spent in the zone that matters.

A threshold session that works

Here's a format that builds real fitness without wrecking you for the rest of the week:

Warm up 15 minutes, building gradually to just under threshold in the final few minutes. Then ride 3 x 12 minutes at 95–100% of FTP, with 5 minutes easy spinning between each. Cool down 10 minutes.

That's roughly 36 minutes of quality work — enough to matter, not so much that you're chasing recovery for three days. Once that becomes manageable, extend the intervals to 15 or 18 minutes, or drop the rest to 3 minutes before you add more time. Progress the volume before you progress the intensity. Riders who go the other way burn out or start missing their numbers halfway through the set.

Reading the session honestly

The best threshold sessions feel controlled for the first two intervals and hard by the last one — not agony, but a real fight to hold the number. If interval one already feels desperate, your target is set too high, or you didn't recover enough from your last hard day. Back it off 3–5% and hit the number instead of blowing up chasing a figure that isn't real that day.

Pay attention to heart rate drift, too. If your power is steady but your heart rate keeps climbing through the interval, that's a sign of accumulating fatigue or dehydration, not necessarily a fitness problem. It's useful data either way — write it down.

How often, and for how long

Twice a week is plenty for most riders balancing this with other training. Three times a week works only if the rest of your training is genuinely easy — threshold sessions are demanding on the nervous system as well as the legs, and stacking too many of them is a fast way to stall progress instead of accelerating it.

Give a threshold block 4 to 6 weeks before you retest. Adaptation here is slower than with VO2max work — you're not just building an engine, you're teaching it to run cleaner at a specific intensity. That takes repetition.

The takeaway

FTP is the scoreboard. Threshold training is the practice that moves it. Structured, steady intervals — done indoors where the resistance doesn't waver — are still one of the most reliable ways to get faster for the effort you put in. Set the number honestly, hold it with discipline, and let the adaptation happen over weeks, not one heroic ride.