(2) REAL-TIME NITRIC OXIDE BIOACTIVITY RESPONSE TO A BOUT OF HIGH- VS. LOW-LOAD RESISTANCE EXERCISE

Purpose: The impact of resistance exercise load on nitric oxide (NO) bioactivity remains unexplored. The purpose of this study was to compare the real-time muscle oxygenation and NO bioactivity response to a bout of high- vs. low-load resistance exercise. Methods: In a randomized, crossover design, sixteen recreationally active men (n=9; 22.9±4.2 y) and women (n=7; 21.1±1.8 y) performed five sets of leg press and three sets of leg extension using either a high-load [70% 1-repetition maximum (1RM)] or low-load (30% 1RM). Muscle oxygenation (SmO₂) and NO bioactivity were monitored using a non-invasive technology (NNOXX One sensor). Results: Although more repetitions were completed across all sets at 30% 1RM compared to 70% 1RM (25.5±9.0 vs.13.4±3.5, respectively, p< 0.001), differences in volume-load were less clear and only specific sex differences were noted. Significant (p< 0.05) pre-to-post set and rest period changes were noted in SmO₂, but primarily in men. In women, SmO₂ remained unchanged across the first three sets of leg press. However, significant (p< 0.05) elevations (from the onset of the first set of leg press) were noted at the start of the fourth set, as well as the beginning of each subsequent leg press and leg extension set. Only a main effect across sets (F=2.6, p< 0.001, ω²=4.4%) was found where NO bioactivity was significantly (p< 0.05) elevated from the start of set one of leg press at the conclusion of all sets, as well as at the start of the fifth set of leg press onward. No significant differences between relative intensity loads were seen for SmO₂ or NO bioactivity on any set when measured as raw values, percent changes and slope across sets and rest periods. Conclusions: No differences in SmO₂ or NO bioactivity were found between the 30% 1RM and 70% 1RM conditions, suggesting similar physiological responses across both low- and high-load resistance exercises. Practical Applications: These findings contribute to the growing body of literature comparing physiological responses and adaptations associated with low-load and high-load resistance exercise. While the mechanisms underlying these responses remain unclear, the study provides a foundation for future research into NO-mediated pathways and their role in muscle adaptation following resistance training. Acknowledgements: None