A latecomer to sport, Sue Reynolds ventured into the world of endurance in an effort to lose weight. Over several seasons, she dropped 200 pounds, evolved into a world-class masters triathlete, and wrote an inspirational book about her transformation. But her curiosity wouldn’t let her stop, so at age 65 she decided to begin working with world-class coaches.

Reynolds shares her personal experiment, chronicling her steep learning curve, the trial and error of new training methods, and the hiring and firing of elite coaches—all of it as she travels the globe, competing (and winning) against the world’s best triathletes. Even as she continues to climb the ranks, her workout data plateaus and her health begins to suffer. She finds herself sidelined by Overtraining Syndrome—a dreaded point of no return for a season, and sometimes a career.

The culture of sport pulls athletes of all ages into an irresistible pursuit of excellence and self-discovery. Left unchecked, this pursuit of peak performance can turn toxic. Across the Line dissects the dynamics of coach-athlete relationships and the unspoken values that shape training, offering athletes a path toward resilience, longevity, and sustainable success.