l-Arginine but not l-glutamine likely increases exogenous carbohydrate oxidation during endurance exercise

Abstract

The addition of L-arginine or L-glutamine to glucose-electrolyte solutions can increase intestinal water, glucose, and sodium absorption in rats and humans. We evaluated the utility of L-arginine and L-glutamine in energy-rehydration beverages through assessment of exogenous glucose oxidation and perceptions of exertion and gastrointestinal distress during endurance exercise. Eight cyclists rode 150 min at 50% of peak power on four occasions while ingesting solutions at a rate of 150 mL 15 min(-1) that contained (13)C-enriched glucose (266 mmol L(-1)) and sodium citrate ([Na(+)] 60 mmol L(-1)), and either: 4.25 mmol L(-1) L-arginine or 45 mmol L(-1) L-glutamine, and as controls glucose only or no glucose. Relative to glucose only, L-arginine invoked a likely 12% increase in exogenous glucose oxidation (90% confidence limits: ± 8%); however, the effect of L-glutamine was possibly trivial (4.5 ± 7.3%). L-Arginine also led to very likely small reductions in endogenous fat oxidation rate relative to glucose (12 ± 4%) and L-glutamine (14 ± 4%), and relative to no glucose, likely reductions in exercise oxygen consumption (2.6 ± 1.5%) and plasma lactate concentration (0.20 ± 0.16 mmol L(-1)). Effects on endogenous and total carbohydrate oxidation were inconsequential. Compared with glucose only, L-arginine and L-glutamine caused likely small-moderate effect size increases in perceptions of stomach fullness, abdominal cramp, exertion, and muscle tiredness during exercise. Addition of L-arginine to a glucose and electrolyte solution increases the oxidation of exogenous glucose and decreases the oxygen cost of exercise, although the mechanisms responsible and impact on endurance performance require further investigation. However, L-arginine also increases subjective feelings of gastrointestinal distress, which may attenuate its other benefits.

Whey or Casein Hydrolysate with Carbohydrate for Metabolism and Performance in Cycling

“…Our finding of no change to the rate of exogenous carbohydrate oxidation with the co-ingestion of either a whey or casein hydrolysate agrees with the previous finding when a whole milk protein concentrate is co-ingested with carbohydrate [37]. However, co-ingestion of the single amino acid arginine increases the rate of exogenous carbohydrate oxidation supposedly via an increase in nitric oxide and intestinal vasodilation [34]. Arginine, although present in both the whey and casein hydrolysates and supplied at a similar rate (~0.5 g/h) as in the study of Rowlands et al [34], may have been absorbed as di and tri-peptides [21,26] and not individual amino acids and thereby may limit the nitric oxide stimulating potential.…”

“…The PL trial served mainly to provide correction for background enrichment and comparison of outcome variables with the PL trial is only done when it aids in supporting identified changes between the 3 energy drink trials. To allow comparison with a large proportion of the recently published studies in this field, data were analysed using probabilistic magnitude-based inferential analysis, which has been recommended as the way forward [1,12] and has been described previously [2,28,29,[33][34][35][36][37]44] for analysing the physiological magnitude of effect. Inferential analysis was performed using published spreadsheets [9,11].…”

Cycling Time Trial Performance May Be Impaired by Whey Protein and L-Alanine Intake During Prolonged Exercise

“…Interestingly, HR was possibly lower with ALA compared with PLA at both 20-and 120-min of the constant-load phase. Perhaps this precipitated from the intestinal cotransport mechanism described above; ALA may have facilitated sodium and water absorption across the gut (Rowlands et al, 2012;Van Loon et al, 1996;Wapnir et al, 1988) thereby preserving plasma volume (Hall et al, 2013) and reducing HR. The importance of this response is questionable though considering that this did not elicit a lower RPE than PLA nor did the lower HR persist into the TT.…”

“…Neutral amino acids are cotransported with sodium across the intestines via glucose independent transporters (Coëffier et al, 2005). Additional sodium absorption across the gut may increase transport of water via solvent drag (Rowlands et al, 2012;Van Loon et al, 1996;Wapnir et al, 1988), which could tenably preserve plasma volume (Hall et al, 2013) and as a result minimize cardiovascular drift (HR) and perceptual strain (Casa et al, 2010). Our data (RPE and HR) suggest that PRO alone does not systematically alter these parameters.…”

“…This notion is logical but it awaits confirmation, as the effects of ingesting PRO calories in isolation have not been examined. Moreover, the potential interactive properties of CHO and amino acids (Rowlands et al, 2012;Wapnir et al, 1997) invites the possibility that PRO may influence performance only when in the presence of exogenous CHO. This study was therefore conceived to evaluate whether a high dose (45 g·hr -1 ) of whey PRO hydrolysate delivered during prolonged cycling influences time trial (TT) performance in the absence of supplemental CHO.…”