Why is the shortest distance 1500 meters? Why is the longest distance 50k? How can I predict performances for shorter races or ultra marathons?

Race Power Calculator uses the Critical Power model to predict your performances from 1500 meters to Marathon.

These race distances are heavily tied to your Critical Power capability.

When you race a distance shorter than 1500 meters or longer than a marathon, other factors besides your Critical Power play a major role in your race plan.

For ultramarathoning, fueling strategy, muscle fatigue, and other factors play a significant role in how you will perform.

You will need to carefully consider these external factors on your own to make a determination for a power target for this kind of race.

Specifically, we recommend this webinar from Andy Dubois for ultra race planning: https://www.youtube.com/watch?v=29UE7khUoS4&t=1s