From the Coach guide
How Coach sets your race pace, splits and warm-up.
Coach uses its estimate for the race, from your threshold test or your best recent runs. It does not use your goal. A goal that your training does not support often goes wrong in the first mile.
Run each mile at the same pace. Do not start fast. If you feel good after the halfway point, you can go faster.
When the forecast feels like 60°F or more, Coach slows your pace by 1% for each 5°F, up to 6%. Above 90°F, run by effort, not by pace. Coach shows the forecast on the day before the race and on race day.
A shorter race starts faster, so it needs a longer warm-up. For a 5K or 10K: 10–15 min easy and 4 strides. For a half: 10 min easy and 2 strides. For a marathon: 5 min easy. The first mile is part of the warm-up.
For a half or a marathon, Coach looks at your recent long runs. If your heart rate rose in the second half of most of them, the plan says to start at this pace or a little slower. The pace does not change. No study links drift to race pace, so Coach gives no number.
Your goal time: what you want to run. Coach shows it beside the estimate. The plan uses the estimate.
Pacing research supports an even effort, and marathon results show slower times in heat. Coach chooses the heat adjustment and warm-ups to give practical starting guidance.
Review of pacing in sport
In events longer than about 2 minutes, athletes who spread their effort more evenly tended to run faster times.
A review across sports, not a trial in recreational runners. A hilly or windy course can need an uneven pace.
Results of 7 marathons over many years
Times got slower as the weather got warmer, from 5 to 25 °C WBGT. The fastest men were 1.7% slower than the course record in the coolest races and 4.5% slower in the warmest. Slower runners slowed more.
The study used marathons and WBGT, which Coach does not have. Coach uses the forecast's feels-like temperature. The size of Coach's change is an app choice.
Coach