Strava, a social network for athletes, in partnership with New Balance, introduced the Strava Back Half Challenge, a two-month campaign that encourages athletes to run a negative split this marathon season.

Beginning on October 9 with the Chicago and Portland Marathons, and ending on December 6 with the California International Marathon, runners who complete the second half of a race faster than the first half and share it on Strava will receive a free pair of New Balance running shoes.

To enter, runners must complete a submission form on the Strava blog after completing a qualifying race. Although negative splitting is a widely recommended race strategy and one used to win the majority of marathons, it’s a feat that only 13% of marathoners accomplish.

Strava’s analysis of six marathons reveals that only 3.6% of Strava athletes who ran the New York City Marathon and 6.3% of those who ran the Boston Marathon completed the second half of a race faster than the first half. Strava created the Back Half Challenge as a way to inspire both new and seasoned runners to challenge themselves to race smart in their fall marathons and run a personal best.