Repeated High-Intensity Exercise Induces Persistent H3K18 Lactylation and Trained Immunity in Human Monocytes: A Randomized Work-Matched Training-Detraining-Rechallenge Trial
Repeated High-Intensity Exercise Induces Persistent H3K18 Lactylation and Trained Immunity in Human Monocytes: A Randomized Work-Matched Training-Detraining-Rechallenge Trial
This randomized, work-matched training-detraining-rechallenge study evaluated whether repeated high-intensity interval training produces persistent functional and epigenetic adaptations in human monocytes. Eighty healthy physically inactive adults aged 18-30 years were randomly assigned in a 2:2:1 ratio to high-intensity interval training (HIIT), moderate-intensity continuous training (MCT), or a non-training control group. HIIT and MCT completed 6 weeks of supervised cycling training matched for external mechanical work, followed by 4 weeks without prescribed structured training. All groups subsequently completed a standardized 30-minute cycling rechallenge. The primary outcome was the between-group difference in change in ex-vivo LPS-stimulated TNF-alpha release from baseline to the post-detraining assessment. Secondary outcomes included IL-6 release, H3K18 lactylation, monocyte subset distribution, blood lactate exposure, chromatin accessibility, H3K18la CUT&Tag occupancy, and RNA-seq transcriptional profiling.
Inclusion
Men and women aged 18-30 years. Healthy adults. Physically inactive, defined as participating in less than 150 minutes per week of structured moderate-to-vigorous exercise during the preceding 6 months.
Exclusion Criteria:
Current tobacco use. Current use of relevant immunomodulatory, anti-inflammatory, corticosteroid, or cardiovascular medications.
Acute infection within 4 weeks before baseline assessment. Musculoskeletal contraindications to maximal cycling exercise. Pregnancy or lactation.
Participants completed baseline cardiopulmonary exercise testing to determine peak oxygen uptake (VO2peak) and maximal aerobic power (MAP). Eligible participants were randomized to HIIT, MCT, or Control. The HIIT intervention consisted of 4 × 4-minute cycling intervals at 85% MAP separated by active recovery at 40% MAP, with standardized warm-up and cool-down periods. The MCT intervention consisted of continuous cycling at 55% MAP for a duration selected to match the external mechanical work of the HIIT sessions. Both exercise groups trained three times per week for 6 weeks.
Blood and monocyte assessments were performed at baseline (T0), 72 hours after the final training session (T1), after 4 weeks without prescribed structured training (T2_PRE), and 120 minutes after a standardized 30-minute cycling rechallenge at 60% of baseline MAP (T3_POST).
Classical monocytes were isolated and stimulated ex vivo with ultrapure Escherichia coli O111:B4 lipopolysaccharide (10 ng/mL) for 24 hours. TNF-alpha was the prespecified primary functional outcome, with IL-6 as a key secondary outcome. Epigenetic and molecular analyses included global H3K18 lactylation, ATAC-seq chromatin accessibility profiling, H3K18la CUT&Tag, and RNA-seq. Blood lactate kinetics and cumulative lactate exposure across the training intervention were also assessed.
The primary comparison was HIIT versus MCT. The Control group served as a supportive non-training reference. Longitudinal outcomes were analyzed using mixed models for repeated measures under the intention-to-treat principle.