- Background Men who have sex with men (MSM) who exercise intensive anaerobic training (IAT) become muscular and physically-attractive, are increasing the number of potential sex-partners and their risk for STI/HIV. This study compared training practises between MSM and heterosexuals, and explored factors associating IAT with sexual-behaviour. Methods This cross-sectional study included a convenient sample of men from 5 Tel-Aviv gyms, who completed anonymous questionnaires regarding their physical training, health and sexual behaviour. Trainees who exercised more than the median anaerobic training-hours were regarded as IAT, and those who performed > one unprotected anal/vaginal-intercourse in the last six months were defined as sexual-risky. Results In 2011, 184 (48%) MSM and 197 (52%) heterosexuals completed the questionnaire. MSM showed a stronger desire to become muscular than heterosexuals, reported more weekly hours of IAT (5.0 and 3.9, respectively, p < 0.001) and used protein-powers or anabolic-steroids more commonly than heterosexuals. MSM reported that the main reasons for training were refining body-shape and improving self-confidence, while heterosexual indicated that weight-loss and health improvement were the main reasons for training. MSM were more sexual-risky than heterosexuals. Of all sexual-risky, 61.9% (N = 70) performed IAT, while 38.1% (N = 43) perform moderate anaerobic training, p < 0.01. This association was stronger among MSM than in heterosexuals (p < 0.01 vs. p = 0.05, respectively). In multivariate analysis, MSM, younger age, dissatisfaction from body shape, strong desire to be more attractive, higher sexual obsession-score, and the use of protein supplement powders predicted an IAT The interaction between MSM and IAT among risky participants was multiplicative. Discussion MSM practised more IAT than heterosexuals, and their interaction between IAT and sexual-risk was multifactorial. MSM community can benefit from holistic approach of sexual-health, addressing body-image and IAT. The gym gay-culture demonstrates how internal dynamics and social norms are possible factors driving MSM to high-risk for HIV.