An unfamiliar heavy or eccentric leg session can blunt endurance performance for one to two days, but the repeated-bout effect sharply reduces this after the first exposure and fades after about 12 weeks without it
Interpretation
Consistent direction across several small studies: 10 trained male cyclists lost about 4.5% of early time-trial power 24 h after an unfamiliar heavy leg session, with lower soreness after a repeat bout (Devantier-Thomas 2024); 17 participants (15 M, 2 F) lost 15-minute time-trial power 48 h after plyometric damage (Burt and Twist 2011); a review concludes residual fatigue can last hours to days (Doma 2017). The repeated-bout effect itself is well established (Hyldahl 2017), lasted 3-6 weeks but not 12 in 48 young men (Theodorou 2026), and a light preconditioning bout protected 26 older men (Chen 2013). Gaps: small samples, mostly men, no triathletes, and almost no running-performance data.
Practical implication
Introduce new leg exercises light, progress load gradually, keep at least 48 hours between an unfamiliar or heavy leg session and key bike or run sessions in the first weeks, and keep lifting through the season so protection isn't lost. Extrapolated from cyclists and lab studies in men, not triathletes.
Sources
7 sources, independently verified.
Two identical heavy leg sessions (3 x 6 at 95% of 6RM; squat, single-leg press, leg extension, leg curl) at least two weeks apart. After the first, soreness rose at 24 and 48 h, countermovement jump fell from 28.3 to 25.5 cm at 24 h, RPE at 90% of VT2 rose about 8%, and power in km 1-3 of a 10 km time trial fell from 281 to 269 W at 24 h (about 4.5%) and to 272 W at 48 h; overall time-trial duration unchanged. Soreness was lower after the second bout. Small, all-male, no control group; percentages calculated from reported means.
Plyometric muscle-damaging exercise produced soreness and strength loss at 48 h; at ventilatory threshold VO2, ventilation and RPE were higher; mean power and distance in a 15-minute cycling time trial were lower with unchanged RPE. Training status not reported in the abstract.
Review of studies measuring endurance performance after single resistance sessions: residual fatigue can impair a subsequent endurance session for several hours to several days if recovery is inadequate, via altered neural recruitment, reduced movement efficiency, muscle soreness and lower glycogen. Recommends adjusting session order, recovery between modes and intensity. Narrative synthesis, not a meta-analysis.
Review describing the repeated bout effect (a single damaging bout protects against damage from a later similar bout) and proposing that neural, mechanical, extracellular-matrix and biochemical adaptations act together; mechanisms remain poorly understood.
Two identical maximal eccentric knee-extensor bouts (5 x 15 at 60°/s) with the second at 3, 6, 9 or 12 weeks. Repeated-bout protection was evident at 3 and 6 weeks for most outcomes, detectable for selected markers at 9 weeks, and absent at 12 weeks (no meaningful effect for torque, range of motion, DOMS, muscle thickness or echo intensity; CK and hs-CRP inconclusive). Young men, isolated eccentric protocol.
A light bout of eccentric knee extensions at 10% of maximal isometric strength, 7 days before a maximal eccentric bout, caused no damage itself but reduced torque and range-of-motion loss, sped recovery and reduced other damage markers after the maximal bout versus controls. Older, untrained men only; isolated knee-extensor protocol.
Meta-analysis of 99 studies comparing post-exercise recovery techniques: massage was most effective for reducing DOMS and perceived fatigue; massage and cold exposure most effective for inflammation markers. Effects on soreness are not necessarily effects on performance.