Provides a Small Advantage in Vertical Jump and Sprint Performance But Does Not Improve Elite Rugby Players' Body Composition.

The present study aimed to examine the effects of supplementation on anthropometrical measurements and physical performance in elite rugby players. Twenty-two elite male Rugby Union players (21-36 years old) volunteered to participate in this study. They were randomly assigned to a group (SPI:  = 11), or a placebo group (PLA:  = 11) in a double-blind design. Subjects were supplemented with (5.7 g/d) or placebo (isoproteic and caloric) for 7 weeks. At baseline (W) and after 7 weeks of supplementation (W), the same anthropometric measurements and physical performance test battery were performed. These tests included isokinetic leg strength and power, vertical jump, speed, and aerobic fitness assessment. For anthropometric data, the fat mass percentage was significantly reduced in both groups without significant difference between groups. While both groups exhibited significant improvements for Squat Jump (SJ), Countermovement Jump (CMJ), and 10- and 30-m sprints between W and W, higher percentage improvements with the SPI group did not reach significance. Neither training alone (PLA) nor training associated with supplementation affected leg maximal strength and power or aerobic fitness. Seven weeks of supplementation in elite rugby players did not improve body composition or substantially increase physical performance. We only observed a non-significant small advantage in vertical jump and sprint performance in the SPI group. Based on the data from this study, supplementation has modest effects in elite rugby players during the competitive phase. Further studies are required to verify supplementation effects among athletes of different sports, ages, genders, and athletic levels with longer durations and higher dosages.