The aim of this study was to evaluate occupational exposure to indoor particulates in fitness clubs. PM2.5 were continuously monitored during the opened periods of ten consecutive days at four fitness clubs (C1–C4) situated in Porto Metropolitan Area, Portugal. Various indoor spaces (main body building areas, studios and rooms for group classes) were assessed. Across the clubs the thermal parameters were within the indicated limits. The obtained PM2,5 ranged between 5–777 μg m−3 with average concentrations (13–43 μg m−3) exceeding the Portuguese limit of 25 μg m−3 at C1–C2, thus highlighting the possible risks for the respective staff. Clubs with mechanical ventilations (C3–C4) demonstrated considerably cleaner air, despite the higher number of clients per day. Long period of the monitoring activities (in the main areas) contributed to the majority of the occupational exposure of the staff; however, dose rates due to class teaching accounted between 30% (males at C3) and 47% (females at C1). These results demonstrate that intense physical activity, even though of short duration, may considerably increase the daily inhalation dose. In addition, female instructors have shown 5–20% higher inhalation doses, thus highlighting the necessity of the gender-consideration when assessing personal exposure.