Lactate threshold or VO2max: which decides your race time?

Two runners, both with a VO2max of 55. One runs ten kilometres in 42 minutes, the other in 48. The difference is not in the ceiling but in how close under it they can sit, and that is called your lactate threshold.

For your race time, that second quantity is often decisive.

Yet almost every conversation in the changing room is about that one number on your watch.

What is your lactate threshold?

Your lactate threshold is the highest effort at which lactate production and clearance are still in balance. Go above it and lactate stacks up faster than your body removes it, and the clock starts running. Your threshold is usually expressed as a percentage of your VO2max, or as a pace and heart rate.

In recreational runners it often sits around 75 to 80 percent of maximum uptake.

In well-trained endurance athletes that can rise above 85 percent. That gap is larger than the difference in VO2max between the same two people, and it is exactly where training changes the most.

What counts as a good VO2max for your age sits in what is a good VO2max.

Which one decides your race time?

All three pillars together, but not equally. Joyner and Coyle described endurance performance as the interplay of VO2max, lactate threshold and efficiency (PMID 17901124). Your VO2max sets the upper limit, your threshold decides which share of it you can hold for an hour, and your efficiency sets how much oxygen each kilometre costs.

The table sets them side by side.

For someone starting out, the ceiling is usually the brake. For someone who has trained for years, it is almost always the threshold.

Does lactic acid cause the burn in your legs?

No, and that is a stubborn misunderstanding. Lactate is a fuel in its own right: your heart and muscles simply burn it. The burning feeling is associated with the hydrogen ions released in the same process and with a falling pH in the muscle.

So lactate is the smoke alarm, not the fire.

That it rises measurably is what makes it useful. That is exactly why sports labs prick your earlobe or fingertip during a step test, because the lactate curve reveals where your balance tips.

Muscle soreness two days later has nothing to do with it, by the way. That was cleared within an hour of your session.

How do you measure your lactate threshold?

Three routes exist: a laboratory step test with finger pricks at rising loads, a 30-minute all-out field test where your average heart rate over the last 20 minutes is your estimate, and the estimate from your sports watch. The first measures lactate properly; the other two derive it.

The watch estimate is the weakest of the three.

A systematic review from December 2025 found wearables usable for VO2max in seven of thirteen studies, but only three studies validated the lactate-threshold estimate (PMID 41477023). So your watch is less well supported on your threshold than on your ceiling.

Do not run a maximal field test if you have symptoms during effort. The Dutch Hartstichting is clear on this: chest pain, dizziness or unexplained breathlessness belong with your GP or a sports physician. What a clinical cycle test does and does not see sits in the exercise stress test explained.

How do you raise your lactate threshold?

With longer blocks just under or around your threshold pace, plus plenty of easy kilometres beneath them. Think of two 20-minute blocks at a pace you could hold for an hour, once a week. That is a different thing from interval training, and it trains something different.

That distinction shows up in the research data.

Helgerud and colleagues saw that threshold training did not measurably raise VO2max in eight weeks, while four times four minutes did, by 7.2 percent (PMID 17414804). That is not evidence that threshold training does nothing: the study looked at VO2max, not at the threshold itself.

That is exactly where most training arguments go wrong. You cannot use a study to dismiss something it never measured.

The interval protocol that does lift your ceiling sits in increasing your VO2max.

Why does your threshold pace drop while you train?

Usually through accumulation: too many hard sessions, too little recovery, or a stretch of poor sleep. Sometimes something in your blood sits underneath it. A low iron store or a low haemoglobin limits your oxygen transport, and your whole curve shifts left.

Your threshold then feels higher than it is.

That is a possible explanation, not a diagnosis. How that chain works and which value belongs to which link sits in cardio fitness and your blood.

If the pace keeps dropping while your load stays level, spotting overtraining through your blood values is the logical next step.

What do you do next?

First work out which of the three pillars is your brake. If you have trained for years and your VO2max sits still, your threshold is where the time is. If you are just starting, interval work will lift your ceiling for years yet.

My suggestion: pick one eight-week block and do not train both at once.

How to record your baseline reliably sits in measuring your VO2max. If you want the blood side alongside it, iron, ferritin and inflammation markers sit together in InsideTracker.

Every blood test result includes a professional assessment from a BIG-registered doctor. For treatment decisions, discuss your results with your GP.

References

• Joyner MJ, Coyle EF. Endurance exercise performance: the physiology of champions. The Journal of Physiology, 2008;586(1):35-44. PMID 17901124.
• Zeleznik Mezan L. Accuracy of wearables for determining the maximal oxygen uptake and lactate threshold: a qualitative systematic review. Frontiers in Sports and Active Living, 2025;7:1707991. PMID 41477023.
• Helgerud J, Hoydal K, Wang E, et al. Aerobic high-intensity intervals improve VO2max more than moderate training. Medicine and Science in Sports and Exercise, 2007;39(4):665-71. PMID 17414804.
• Hartstichting. Exercise and your heart rate.