The repeated-bout effect following eccentric knee-extensor exercise was evident at 3 and 6 weeks, remained detectable for selected markers at 9 weeks, but was no longer meaningfully present at 12 weeks for most outcomes.
Key Findings
Results
The repeated-bout effect was evident across most outcomes when the second eccentric exercise bout was performed 3 weeks after the first.
48 young men performed two identical bouts of maximal eccentric knee-extensor exercise (5 × 15 repetitions at 60°/s)
Four independent groups (n=12 each) performed the second bout at 3, 6, 9, or 12 weeks after the first
Outcomes assessed included isometric torque, ROM, DOMS, muscle thickness, echo intensity, CK, and hs-CRP
Assessments were made before and 2 and 4 days after each bout
Results
The repeated-bout effect was still evident across most outcomes when the second bout was performed 6 weeks after the first.
Protection was observed across most measured markers at the 6-week interval
Baseline-adjusted linear mixed-effects models were used to compare responses between bouts
Results
The repeated-bout effect remained detectable at 9 weeks but only for selected markers rather than across most outcomes.
At 9 weeks, the protective effect was present for some but not all measured outcomes
This represents a partial attenuation of the repeated-bout effect compared to the 3- and 6-week intervals
The 9-week finding suggests a gradual decay of the protective adaptation rather than an abrupt disappearance
Results
At 12 weeks, no significant differences between bouts were observed at either day 2 or day 4 for any outcome.
Equivalence testing was used at the 12-week interval to complement null hypothesis significance testing
Equivalence analyses indicated the effect was no longer meaningfully present for isometric torque, ROM, DOMS, muscle thickness, and echo intensity
Findings for CK and hs-CRP at 12 weeks remained inconclusive based on equivalence testing
The absence of significant between-bout differences at both post-exercise time points (day 2 and day 4) supports the conclusion that the repeated-bout effect had dissipated by 12 weeks
Results
Biochemical markers CK and hs-CRP showed inconclusive results at 12 weeks, unlike functional and structural markers which showed equivalence.
Exploratory equivalence analyses confirmed loss of meaningful effect for isometric torque, ROM, DOMS, muscle thickness, and echo intensity at 12 weeks
CK and hs-CRP did not reach equivalence conclusions at 12 weeks, leaving their time course less certain
This suggests that different categories of muscle damage markers may have different time courses for the repeated-bout effect
Conclusions
The time course of the repeated-bout effect has practical implications for the design of muscle damage studies and scheduling of eccentric training sessions.
The authors state this time course 'can guide the design of muscle damage studies and the scheduling of eccentric training sessions'
Studies using a repeated-bout design should ensure the second bout occurs within a window where protection is still meaningful
The 9-week partial and 12-week full dissipation findings provide concrete washout period guidance for researchers
Results indicate the protective effect may persist for some outcomes for up to 9 weeks
What This Means
This research suggests that when people perform a bout of intense eccentric (muscle-lengthening) exercise, their muscles become temporarily more resistant to damage from a second identical exercise session — a phenomenon known as the 'repeated-bout effect.' The study tested how long this protection lasts by having 48 young men perform two sessions of maximal knee-extension eccentric exercise, with different groups waiting either 3, 6, 9, or 12 weeks between sessions. The researchers measured muscle soreness, strength loss, range of motion, muscle swelling, and blood markers of inflammation and muscle damage before and after each session.
The findings show that the protective effect was clearly present when the second session was done 3 or 6 weeks after the first, meaning the muscles showed noticeably less damage and soreness the second time around. At 9 weeks, some protection was still detectable but only for certain measures. By 12 weeks, no meaningful protection remained for most outcomes — the muscles responded to the second session essentially as if it were a first-time experience. Blood-based markers of muscle damage (creatine kinase and C-reactive protein) were harder to interpret at 12 weeks, leaving some uncertainty about their exact time course.
This research matters for both scientists and people who train using eccentric exercise methods. For researchers, it means that muscle damage studies using a repeated-bout design need to carefully control the timing between sessions, and a 12-week gap is likely sufficient to 'wash out' prior adaptation. For those involved in planning athletic or rehabilitation training, it suggests that the protective benefits of a previous hard eccentric workout session may largely wear off within about 9–12 weeks, informing how frequently such training sessions might need to be repeated to maintain adaptation.
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Theodorou A, Margaritelis N, Karyofyllidou A, Christodoulou F, Jamurtas A, Fatouros I, et al.. (2026). The Duration of the Repeated-Bout Effect After Eccentric Exercise.. Scandinavian journal of medicine & science in sports. https://doi.org/10.1111/sms.70381