Race Shape › Answers › How does altitude affect running pace?
AnswersHow does altitude affect running pace?
The same effort produces a slower pace at altitude, because there is less oxygen in each breath. Race Shape slows prescribed paces by roughly 2% for every 300 m above 500 m — about 8% in Johannesburg at 1 753 m. That is a planning rule rather than a precise measurement, and acclimatised athletes lose less, but training to sea-level paces at altitude reliably means training too hard.
The correction in South African towns
| Town · altitude | Pace correction · easy ceiling for a 25:00 5 km |
|---|---|
| Durban · 8 m | 0.0% · easy 6:19/km |
| Cape Town · 25 m | 0.0% · easy 6:19/km |
| Pietermaritzburg · 596 m | 0.6% · easy 6:22/km |
| Kimberley · 1 197 m | 4.6% · easy 6:37/km |
| Polokwane · 1 310 m | 5.4% · easy 6:40/km |
| Pretoria · 1 339 m | 5.6% · easy 6:41/km |
| Bloemfontein · 1 395 m | 6.0% · easy 6:42/km |
| Midrand · 1 600 m | 7.3% · easy 6:47/km |
| Johannesburg · 1 753 m | 8.4% · easy 6:51/km |
Correct only for the difference
What matters is the difference between where you tested and where you run. A Johannesburg runner who races in Cape Town should expect the same effort to be quicker on the day. A Durban runner racing Soweto should expect it to be slower. Correcting twice — once for where you trained and again for where you race — is the error to avoid, and the plan does it once.
Heart rate is a useful cross-check at altitude, because it responds to the real cost of the effort. On the first few days after travelling up, expect it to run high at paces that normally feel easy.
Common questions
How long does it take to acclimatise?
Some adaptation starts within days, but meaningful adaptation takes weeks. Athletes who live at altitude are already adapted to it.
Is it better to train at altitude?
It can help some athletes, but it also makes hard sessions harder to hit. For most amateurs the practical point is simply to adjust paces rather than chase coastal numbers.
Does altitude affect cycling power too?
Yes. The plan takes about 6% per 1 000 m above 500 m off power, and less for a rider who lives at altitude.
Sources
- Race Shape engine rule: roughly 2% per 300 m above 500 m for running pace, applied to the difference between test and training altitude.