Objective: It remains unknown whethermyonuclei remain elevated post anabolic-androgenic steroid (AAS) usage in humans. Limited data exist on AAS-induced changes in gene expression. Design: Cross-sectional/longitudinal. Setting: University. Participants: Fifty-sixmen aged 20 to 42 years. IndependentVariables: Non-resistance-trained (C) or resistance-trained (RT), RT currently using AAS (RT-AS), of which if AAS usage ceased for$18 weeks resampled as Returning Participants (RP) or RT previously using AAS (PREV). MainOutcomeMeasures: Myonuclei per fiber and cross-sectional area (CSA) of trapeziusmuscle fibers. Results: There were no significant differences between C (n 5 5), RT (n 5 15), RT-AS (n 5 17), and PREV (n 5 6) for myonuclei per fiber. Three of 5 returning participants (RP1-3) were biopsied twice. Before visit 1, RP1 ceased AAS usage 34 weeks before, RP2 and RP3 ceased AAS usage#2 weeks before, and all had 28 weeks between visits. Fiber CSA decreased for RP1 and RP2 between visits (7566 vs 6629 mm2; 7854 vs 5677 mm2) while myonuclei per fiber remained similar (3.5 vs 3.4; 2.5 vs 2.6). Respectively, these values increased for RP3 between visits (7167 vs 7889 mm2; 2.6 vs 3.3). Conclusions: This cohort of past AAS users did not have elevated myonuclei per fiber values, unlike previous research, but reported AAS usage was much lower. Training and AAS usage history also varied widely among participants. Comparable myonuclei per fiber numbers despite decrements in fiber CSA postexposure adheres with the musclememory mechanism, but there is variation in usage relative to sampling date and low numbers of returning participants. [ABSTRACT FROM AUTHOR]