Citrus aurantium supplementation in strength exercise: a crossover, randomized and double-blind clinical trial

Synephrine, found in Citrus aurantium (CA), is commonly used in supplements aimed at enhancing performance, energy, and weight loss. Objective: To evaluate the acute effects of CA on performance during resistance exercise. Methods: A randomized, double-blind, crossover clinical trial was conducted with 10 trained men (≥6 months of strength training). Markers of muscle damage (CK, LDH), blood pressure (SBP, DBP), heart rate (HR), performance, and fatigue were assessed before and after exercise. Following supplementation, participants performed five sets of bench press at 70% of 1RM in two sessions, one week apart. Data were expressed as mean ± SD. Normality was assessed using the Shapiro-Wilk test. Data were analyzed using repeated measures ANOVA, paired t-tests, and multiple comparisons. Analyses were performed using SPSS v21.0 (IBM), with significance set at p ≤ 0.05. Results: The CA condition showed a trend toward a higher total number of repetitions compared to placebo (p=0.018). Lactate levels were significantly higher after exercise with CA (p=0.048). No significant differences in CK and LDH were found between conditions (p=0.0051); however, a significant increase in CK was observed 12 hours post-exercise in both groups (p=0.0001). CA supplementation reduced pre-exercise SBP (p=0.049) but increased post-exercise SBP (p=0.0002). HR increased both pre- and post-exercise (p=0.0001), and sympathetic activation was observed pre-exercise in the CA group (p=0.005). Conclusion: CA improves performance and delays fatigue during resistance training by stimulating the sympathetic nervous system.