What is Fatigue (ATL)?

Acute Training Load (Fatigue) combines duration and intensity to provide a value of how much an athlete has recently trained. TrainingPeaks calculates ATL, by default, as the exponentially weighted average of daily TSS for the past 7 days.  Note that, in effect, ATL represents the training an athlete has done in the past two weeks given the nature of exponentially weighted averages. 

Formula

ATLtoday = ATLyesterday + (TSStoday - ATLyesterday)(1/ATL time constant)

Since ATL is determined within a window of seven days and based on the moving average within it, it provides the runner with a snapshot of recent trends in fatigue comparing today’s fatigue with yesterday's.

Last evening, I participated in the Tuesday Night Track (TNT) workout at Occom Pond for the first time in years. Driving to Hanover over King Hill Road, the waxing crescent moon, a brilliant white in a red-orange sky, smiled at me as the yellow sun dipped beneath the Green Mountains on the horizon. I slowed my Jeep at the crest of the hill and let it all soak in.

Standing in the introduction circle before the workout started, I looked around and saw four runners I recognized from the past. Cara led the group. Ten years ago, I led the group and Cara humbly introduced herself. I knew immediately that she had the heart of a true runner and after introductions I sidled over to her to gauge her interest in racing for UVRC’s NHGP racing team.

Given the eerily warm temperature, the mile loop around the pond was crowded with runners and walkers, mostly Dartmouth College students. Head lamps danced and reflection vests flickered. I took my place at the back of the pack and shuffled along for five laps including 4 x 800 with 400 recovery. I pushed on the final interval until my left calf tightened, then backed off and walked down the hill by the golf course to my Jeep. There I met Tim, who served as UVRC President before my three years at the helm. We chatted happily until a chill lowered over us.

Runners streamed by, head lamps flashing as they completed their cooldown. At 74 years I was the oldest participant, and the average age of the group is now around 30. I am inspired by their youthful enthusiasm.