Purpose <p>This study compared the impact of hypoxic air quality breathing in two normobaric hypoxia (NH) environments (a tent with high carbonic levels and relative humidity [NHTent] vs. a room with normal carbonic levels and relative humidity [NHRoom]) on the outcomes of an 8-week resistance training (R_T) program.</p> Methods <p>Twenty-four trained men (age: 22 ± 3 years; weight: 76.32 ± 11.01&#xa0;kg; height: 176.79 ± 7.48&#xa0;cm) were assigned to either the NHTent or the NHRoom group being exposed to the same FiO₂ (15.9%) to analyze the impact of two different procedures to generate intermittent NH on structural, physiological, functional, and perceptual responses after a R_T program. CO₂ and relative humidity levels were measured before and after each training session. Physiological variables (heart rate [HR] and SpO₂) were monitored and used for comparison between the first and last training sessions. Functional (bench press and squat 1RM) and structural (vastus lateralis thickness) responses were measured before and after the program.</p> Results <p>CO₂ and relative humidity levels were higher in the NHTent (<i>p</i> &lt; 0.001). Compared to NHRoom, NHTent group displayed higher HR (<i>p</i> = 0.002), lower SpO₂ (<i>p</i> = 0.014), greater increases in 1RM (<i>p</i> = 0.011) and lower increases in vastus lateralis thickness (<i>p</i> = 0.06). </p> Conclusion <p>These findings suggest that the CO₂ and relative humidity levels on the hypoxic air breathed during training alter the physiological response to the R_T. The harsher environment seems to enhance neuromuscular adaptations but limit hypertrophic responses. Results highlight the need to control environmental factors carefully when simulating NH conditions for training purposes.</p>