Combined Effects of Citrulline Plus Nitrate-Rich Beetroot Extract Co-Supplementation on Maximal and Endurance-Strength and Aerobic Power in Trained Male Triathletes: A Randomized Double-Blind, Placebo-Controlled Trial.

Josefa González-Santos,Diego Fernández-Lázaro,Aitor Viribay,José Burgos,Juan Mielgo-Ayuso,Julio Calleja-González

doi:10.3390/nu14010040

Abstract

Citrulline (CIT) and nitrate-rich beetroot extract (BR) are ergogenic aids and nitric oxide (NO) precursors. In addition, both supplements seem to have other actions at the level of muscle metabolism that can benefit strength and aerobic power performance. Both supplements have been studied in numerous investigations in isolation. However, scientific evidence combining both supplements is scarce, and to the best of the authors’ knowledge, there is no current study of endurance athletes. Therefore, the main purpose of this study was to determine the effect of 9 weeks of CIT plus BR supplementation on maximal and endurance-strength performance and aerobic power in male triathletes. This study was a randomized double-blind, placebo-controlled trial where participants (n = 32) were randomized into four different groups: placebo group (PLG; n = 8), CIT plus BR group (CIT- BRG; 3 g/kg/day of CIT plus 3 mg/kg/day of nitrates (NO3−); n = 8), CIT group (CITG; 3 g/kg/day; n = 8) and BR group (BRG; 3 mg/kg/day of NO3−; n = 8). Before (T1) and after 9 weeks (T2), four physical condition tests were carried out in order to assess sport performance: the horizontal jump test (HJUMP), handgrip dynamometer test, 1-min abdominal tests (1-MAT) and finally, the Cooper test. Although, no significant interactions (time × supplementation groups) were found for the strength tests (p > 0.05), the CIT- BRG supplementation presented a trend on HJUMP and 1-MAT tests confirmed by significant increase between two study moments in CIT-BRG. Likewise, CIT-BRG presented significant interactions in the aerobic power test confirmed by this group’s improve estimated VO2max during the study with respect to the other study groups (p = 0.002; η2p = 0.418). In summary, supplementing with 3 g/day of CIT and 2.1 g/day of BR (300 mg/day of NO3−) for 9 weeks could increase maximal and endurance strength. Furthermore, when compared to CIT or BR supplementation alone, this combination improved performance in tests related to aerobic power.

Highlights

The triathlon is an event that combines the disciplines of swimming, cycling and running in this sequential order [1,2]
All triathlons can be considered as events in which aerobic power predominates, since the physiological parameters associated with endurance training are considered as relevant; maximal oxygen consumption (VO2max ), anaerobic/ventilatory threshold and economy of movement, among others [3,4]
The data obtained on body composition and somatotype showed no significant differences (p > 0.05) in the group-time interaction (Table 1)

Summary

Introduction

The triathlon is an event that combines the disciplines of swimming, cycling and running in this sequential order [1,2]. All triathlons can be considered as events in which aerobic power predominates, since the physiological parameters associated with endurance training are considered as relevant; maximal oxygen consumption (VO2max ), anaerobic/ventilatory threshold and economy of movement, among others [3,4]. The high physical demands of this sport make nutritional recommendations insufficient, so triathletes resorts to nutritional supplements to improve their sport performance [6]. There is increasing scientific evidence of the benefits that nitric oxide (NO) precursors (L-citrulline (CIT) and supplements rich in nitrates (NO3 − ) such as beetroot juice or nitrate-rich beetroot extract (BR) provide for sports performance, since these ergogenic aids could improve both aerobic and anaerobic metabolism [7]. The NO is synthesized by oxidation of the amino acid L-arginine (ARG), which comes from

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