When it comes to marathons, Christine Rockey has just about seen it all.

She’s served as a pacer for close to 30 of the 96 marathons she’s run, giving her an up-close view of all the helpful and harmful behaviors runners exhibit on race day.

According to Rockey, who is an RRCA-certified run coach, certification instructor, and principal lecturer at Coastal Carolina University, there’s one signal that a runner in her group won’t make it to the finish line at their goal pace.

To help you run a better race, Rockey explains exactly why this mistake causes you to slow down midrace and how to avoid the issue so you can finish your next 26.2 with a PR.

The Biggest Red Flag You Won’t Hit Your Marathon Goal

Breathing hard—or “panting,” as Rockey says—is a dead giveaway that a runner is working way too hard for the marathon pace they’re trying to hold, especially early in the race.…