Apple Watch freezes during run

i used my Apple Watch during a 21K run. i used the Workout app to monitor my heart rate during the race.

after the halfway mark, the screen dimmed, and the display froze. (distance stopped adding, and the heart rate was replaced by "-- --".

thinking that it was because of excessive sweat on the sensors, i tried to wipe the back of the watch as best i could (which is not much considering everything i had on me was wet). pressing the Digital Crown to return the display to the watch face, but every time i would go to the Workout app it would show the same frozen display.

it was only after a kilometer (approx 7 minutes) did the Workout app respond, and worked normally until the end of the run.

so as far as the Workout app on my Apple watch was concerned, i had only run 19.71km instead of the 21K that i actually ran.

question: how do i prevent this from happening again?