Abstract

Background/Objectives: 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 (SmO₂) and NO bioactivity response to a bout of high- versus low-load resistance exercise. Methods: In a randomized, crossover design, 16 recreationally active males (n = 9; 22.9 ± 4.2 years) and females (n = 7; 21.1 ± 1.8 years) performed 5 sets of leg press and 3 sets of leg extension using either a high load (70% 1 repetition maximum [1RM]) or low load (30% 1RM). SmO₂ and NO bioactivity were indirectly monitored using a noninvasive technology (NNOXX One sensor). Results: Although more repetitions (P < .001) were completed across all sets at 30% 1RM (25.5 ± 9.0) compared with 70% 1RM (13.4 ± 3.5), differences in volume load were less clear and only specific sex differences were noted. Significant (P < .05) pre-to-post set and rest period changes were noted in SmO₂ but primarily in males. In females, SmO₂ remained unchanged across the first 3 sets of leg press. However, significant (P < .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 < .001, ω² = 0.044) was found where NO bioactivity was significantly (P < .05) elevated at the conclusion of all sets when compared with the start of set one of leg press, as well as at the start of the fifth set of leg press onward. No 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 physiologic responses across both low- and high-load resistance exercises.