Acute oral administration of a tyrosine and phenylalanine-free amino acid mixture reduces exercise capacity in the heat

Abstract

Acute tyrosine administration is associated with increased exercise capacity in the heat. To explore whether reduced plasma tyrosine and phenylalanine (tyrosine precursor) is associated with impaired exercise capacity in the heat, eight healthy, moderately trained male volunteers, unacclimated to exercise in the heat, performed two tests in a crossover design separated by at least 7 days. In a randomised, double-blind fashion, subjects ingested 500 mL flavoured, sugar-free water containing amino acids [(TYR-free; isoleucine 15 g, leucine 22.5 g, valine 17.5 g, lysine 17.5 g, methionine 5 g, threonine 10 g, tryptophan 2.5 g)] to lower the ratio of plasma tyrosine plus phenylalanine:amino acids competing for blood-brain barrier uptake (CAA), a key determinant of brain uptake, or a balanced mixture (BAL; TYR-free plus 12.5 g tyrosine and 12.5 g phenylalanine). One hour later, subjects cycled to exhaustion at 63 ± 5 % [Formula: see text]O2peak in 30 °C and 60 % relative humidity. Pre-exercise ratio of plasma tyrosine plus phenylalanine:ΣCAA declined 75 ± 5 % from rest in TYR-free (P < 0.001), but was unchanged in BAL (P = 0.061). Exercise time was shorter in TYR-free (59.8 ± 19.0 min vs. 66.2 ± 16.9 min in TYR-free and BAL respectively; P = 0.036). Heart rate (P = 0.298), core (P = 0.134) and skin (P = 0.384) temperature, RPE (P > 0.05) and thermal sensation (P > 0.05) were similar at exhaustion in both trials. These data indicate that acutely depleting plasma catecholamine precursors:ΣCAA is associated with reduced submaximal exercise capacity in the heat.

The effect of bovine colostrum supplementation on intestinal injury and circulating intestinal bacterial DNA following exercise in the heat

“…Participants performed 60 min of treadmill running at 70% . Core body temperature, heart rate (HR), rating of perceived exertion (RPE) [ 26 ], and thermal sensation were recorded using a 21-point scale ranging from − 10 (cold impossible to bear) to + 10 (heat impossible to bear) (used previously in our laboratory during nutritional studies of exercise in the heat by Tumility et al [ 27 , 28 ]) every 10 min during the trial. Fluid (ordinary tap water) was provided to participants at a rate of 2.5 mL kg body mass −1 every 20 min during exercise.…”

Is it time to turn our attention toward central mechanisms for post-exertional recovery strategies and performance?

“…Dopamine stimulating drugs are known to enhance aspects of exercise performance (Roelands et al, 2008 ), thus BCAA administration may benefit from the addition of tyrosine in any supplementation routine. Certainly, acutely depleting plasma tyrosine results in reduced exercise capacity (Tumilty et al, 2013 ). Further work in this area is required.…”

Neurophysiological effects of exercise in the heat

“…The authors could not pinpoint the reason for this contradictory finding, but one aspect that might be of importance is the source of the tyrosine, which came from an online sport nutrition company in the study of Tumilty et al (2011) and from a medical nutrition supplier in the study of Watson et al (2012). Tumilty et al (2013) repeated the same experimental protocol, but depleted the availability of tyrosine and phenylalanine. This manipulation led to a significant decrease in the time to exhaustion, providing further evidence that the availability of catecholamine precursors is important during prolonged exercise in the heat (Tumilty et al, 2013).…”

“…() repeated the same experimental protocol, but depleted the availability of tyrosine and phenylalanine. This manipulation led to a significant decrease in the time to exhaustion, providing further evidence that the availability of catecholamine precursors is important during prolonged exercise in the heat (Tumilty et al., ). Thus far, all studies examining the effects of oral tyrosine administration had used a time‐to‐exhaustion protocol.…”