Research · 4 min read · 2026-10-12
Can you find your critical speed without a lab?
Critical speed marks the fastest pace you can sustain without fatigue building steadily. Studies show it can be estimated from your own runs and a few time trials.
Critical speed is one of the most useful numbers in running. It marks roughly the fastest pace you can hold before fatigue starts to build up steadily. Do you need a lab to find it? Several studies say no.
Why critical speed matters
In a study of ten well-trained runners, oxygen uptake stayed stable just below critical speed but kept rising just above it. The researchers concluded that critical speed marks the upper limit of what the body can sustain in a steady state better than a common lactate-based threshold.
What the researchers did
One group of researchers used the training logs of more than 25,000 recreational runners. From each runner's fastest efforts over several distances, they calculated critical speed without any extra testing.
Another group asked 23 recreational runners to wear a foot pod for eight weeks. They compared critical speed calculated from six weeks of normal training with results from three maximal time trials of 3, 7 and 12 minutes, and with 3-minute all-out tests.
What they found
In the large study, critical speed calculated from training data was linked to marathon performance and helped explain who slowed down late in the race.
In the smaller study, the different methods gave similar values for critical speed, and repeated tests gave very consistent results. The estimate of how much work can be done above critical speed was much less consistent between methods.
What it means for you
If you run hard efforts of different lengths now and then, your training already contains much of the information needed to estimate critical speed. A few maximal time trials on separate, well-rested days can make the estimate more precise. The researchers allowed at least 24 hours between efforts and recommended 48.
What the studies can't tell you
Training data only works if some runs are truly hard efforts. An estimate is not the same as a lab measurement, and for the individual runner the methods can still differ.
How we use it
PX7 Training builds your targets from your own races, tests and runs. A maximal test is only suggested when it suits you, and you don't need a lab.
Sources
- Nixon et al. (2021), Steady-state VO₂ above MLSS: evidence that critical speed better represents maximal metabolic steady state in well-trained runners. European Journal of Applied Physiology.
- Smyth & Muniz-Pumares (2020), Calculation of critical speed from raw training data in recreational marathon runners. Medicine & Science in Sports & Exercise.
- Hunter, Ledger & Muniz-Pumares (2023), Remote determination of critical speed and critical power in recreational runners. International Journal of Sports Physiology and Performance.
Written by Jørgen Larsen for PX7 Training.