The Repeated-Bout Effect

Picture from Iwannaburnfat

Those of you who are preparing for races with long downhills (like Boston) or trail races may want to know this. Or even personal trainers and strength coaches getting their athletes to do eccentric exercises.

If the long descent (or an eccentric exercise) is unaccustomed, it can cause muscle damage, soreness and a loss of strength (or delayed onset of muscle soreness - DOMs). However, repeating the same activity causes far less damage the second time. This protection is known as the repeated-bout effect. It is not commonly known how long the protection lasts. Let's see what the latest research found.

48 young males were recruited for this study. They did 2 identical exercise sessions where 5 sets maximal knee extension (straightening) exercise was peformed. Each set consisted of 15 repetitions at 60°/ sec.

4 independent groups performed the second bout of exercise 3, 6, 9 and 12 weeks after the first bout of exercise. 

Range of motion, delayed onset of muscle soreness (DOMs), muscle thickness (swelling), isometric torque (strength), echo intensity (tissue quality/ fluid accumulation), creatine kinase and high sensitivity C-reactive protein (hs-CRP) were assessed before, 2 and 4 days after each exercise bout.

Since the participants started with different levels of strength, soreness and blood markers, the researchers measured the subjects at baseline and then adjusted future data points based on their starting numbers. This allows the resarchers to evaluate how much strength each participant lost or recovered, rather than their raw strength.

The repeated bout effect was still present after 3 and 6 weeks across most outcomes and certain markers were still detectable after 9 weeks. At 12 weeks, all the protective effects were gone.

Please note that this study was done on young men performing isolated knee extension on a machine so some differences in timeline can differ in downhill running, for women and older runners.

So those of you preparing for races with long descents should ideally run a downhill-specific session every 3-4 weeks so your repeated-bout effect protection is intact. After a 3 month break or more or after the off-season, the first downhill session should be treated like a new first session. 

Picture from Iwannaburnfat

For strength coaches or personal trainers planning eccentric strength training cycles (like Nordic curls) to build injury resilience, you need to repeat the exercises within 6 weeks to maintain the protective adaptations. 

Reference

Theodorou AA, Margaritelis NV, Karyofyllidou et al (2026). The Duration Of The Repeated-Bout Effect After Eccentric Exercise. Scan J of Med & Sci Sp. e70381. DOI: 10.1111/sms.70381