Anyone who has taken a break from working out knows the soreness that can occur when you return to training. Typically, that soreness isn’t nearly as severe after subsequent similar workouts. The reason has been something of a mystery; however, a 2016 report offers a clue that may help us understand the phenomenon.

The small study, conducted at Brigham Young University, in Provo, Utah, and published in Frontiers in Physiology (2016;, featured seven men and seven women who completed a vigorous, soreness-inducing exercise session and then repeated the same workout 28 days later. Muscle biopsies were taken before and after each workout session.

According to study participants, feelings of soreness were much less intense after the second session than they were after the first bout. When analyzing the biopsies, the researchers were surprised to discover increased T-cell presence in the sample taken after the second workout.

“You think of T-cells as responding to infections, not repairing muscles—but we found a significant accumulation of T-cells infiltrating damaged muscle fibers,” said Robert Hyldahl, PhD, assistant professor of exercise science at BYU, in a press release. “Our study is the first to show T-cells present in human muscle in response to exercise-induced damage.”

Lead study author and graduate student Michael Deyhle added, “Many people think inflammation is a bad thing. But our data suggest when inflammation is properly regulated it is a normal and healthy process the body uses to heal itself.”

Ryan Halvorson

Ryan Halvorson is an award-winning writer and editor. He is a long-time author and presenter for IDEA Health & Fitness Association, fitness industry consultant and former director of group training for Bird Rock Fit. He is also a Master Trainer for TriggerPoint.

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