If it’s your first time doing CP test we recommend 6 laps first, 3 laps second.
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Most people don’t know how to pace themselves in the 3 laps run because it’s really fast. (Faster than your mile pace!). Lots of them end up doing mile or 3k pace in the 3 laps test, then doing 3k pace in the 6 laps test, which makes the CP result inaccurate.
What we found out is that if we ask people to run 6 laps first, they understand the intensity of 6 laps, then they naturally pick the higher intensity for 3 laps. It produces more accurate result.
If you are experienced and know what you are doing, then the order doesn’t matter much.