Effects of Acute Red Spinach Powder (VitaSpinach^®) Ingestion on Muscular Endurance and Resistance Exercise...

Introduction: Red spinach powder (RSP) contains high amounts of inorganic nitrate/nitrite (NO₃/NO₂), which has been suggested to alter vascular activity, cognitive processing, and sprint exercise performance. There have been few investigations as to whether RSP serves as an ergogenic aid to improve resistance exercise performance, particularly muscular endurance. Purpose: The purpose of this study was to investigate acute RSP (VitaSpinach^®) supplementation on muscular endurance and velocity during bench press exercise. Methods: In a double-blind, counterbalanced crossover manner, resistance-trained males (n = 14) were subjected to two supplement conditions as follows: (1) placebo (PL; purple sweet potato) or (2) red spinach powder (RSP; 400 mg NO₃). Supplements were consumed 2 h prior to exercise and blood was collected immediately pre-exercise to determine NO₃/NO₂ levels. To determine barbell velocity, participants completed two sets × two repetitions with maximal effort, while a rotary encoder measured mean barbell velocity. Following this, participants performed three sets × repetitions to exhaustion (RTE) at 60% of 1-Repetition Maximum (1-RM), separated by 2 min of rest, to determine muscular endurance. Local (lRPE) and global (gRPE) ratings of perceived exertion were measured after exercise. Blood NO₃/NO₂, RTE, mean velocity, lRPE, and gRPE were compared between supplement conditions. Results: RSP resulted in significantly higher blood levels of total NO₃/NO₂ (p < 0.001) compared to PL. RSP did not result in superior total RTE (p = 0.935) but increased mean velocity (p = 0.035) compared to PL. Both lRPE (p = 0.027) and gRPE (p = 0.028) were significantly reduced with RSP supplementation. Conclusions: Findings suggest acute RSP ingestion increased NO₃/NO₂ and bench press velocity. While muscular endurance remained unchanged, RSP resulted in lower perceptions of exertion.