This study examined neurohumoral alterations during prolonged exercise with and without hyperthermia. The cerebral oxygen-to-carbohydrate uptake ratio (Odos/CHO = arteriovenous oxygen difference divided by arteriovenous glucose difference plus one-half lactate), the cerebral balances of dopamine, and the metabolic precursor of serotonin, tryptophan, were evaluated in eight endurance-trained subjects during exercise randomized to be with or without hyperthermia. The core temperature stabilized at 37.9 ± 0.1°C (mean ± SE) in the control trial, whereas it increased to 39.7 ± 0.2°C in the hyperthermic trial, with a concomitant increase in perceived exertion (P < 0.05). At rest, the brain had a small release of tryptophan (arteriovenous difference of ?1.2 ± 0.3 ?mol/l), whereas a net balance was obtained during the two exercise trials. Both the arterial and jugular venous dopamine levels became elevated during the hyperthermic trial, but the net release from the brain was unchanged. During exercise, the O2/CHO was similar across trials, but, during recovery from the hyperthermic trial, the ratio decreased to 3.8 ± 0.3 (P < 0.05), whereas it returned to the baseline level of ?6 within 5 min after the control trial. 2/CHO was established by an increased arteriovenous glucose difference (1.1 ± 0.1 mmol/l during recovery from hyperthermia vs. 0.7 ± 0.1 mmol/l in control; P < 0.05). The present findings indicate that the brain has an increased need for carbohydrates during recovery from strenuous exercise, whereas enhanced perception of effort as observed during exercise with hyperthermia was not related to alterations in the cerebral balances of dopamine or tryptophan.
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To the Editor: Nybo et al. (3) examined the relationship between the arterial concentration of free tryptophan (TRP) and the arteriovenous concentration difference of free TRP across the brain. The correlation coefficient between these two variables was reported to be 0.54 (P < 0.05). Nybo et al. proposed that this significant relationship supported their main research hypothesis that “serotonin levels in the brain could increase when exercise elevates the plasma concentration of free TRP.” Although we do not necessarily disagree with the possibility that this hypothesis is true, we maintain that the correlation analysis, which was employed to arrive at this conclusion, is spurious.
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A spurious correlation between a couple variables is defined as one which might happen from the absence of any genuine organic outcomes of the latest variables (4). The fresh variables that have been synchronised because of the Nybo et al. (3) aren’t independent, no matter what people physiological elements which can be hypothesized so you’re able to connect her or him together. Arterial 100 % free TRP was you to definitely changeable in the analysis, it was also mixed https://datingranking.net/es/los-mejores-sitios-de-citas/ up in computation of one’s most other variable to get coordinated facing it (arteriovenous concentration improvement off totally free TRP). Hence, both variables that were synchronised are generally linked mathematically, and a significant moderate-to-highest relationship between those two parameters will be asked that have people values away from arterial and you may venous free TRP. It artifact might have been recognized for ages (4) and you will try recently proven to be expose because of the Atkinson ainsi que al. (1) in certain clinical tests on the cycling abilities. We could show brand new relevancy associated with the artifact for the investigation from Nybo ainsi que al. (3) with the help of a document simulation.
We generated two sets of random data (n = 40) representing arterial and venous free TRP concentrations within the same physiological ranges as reported by Nybo et al. (3). Both sets of data were normally distributed and completely unrelated (the correlation coefficient between our hypothetical arterial and venous free TRP concentrations was 0.02). We then calculated the arteriovenous concentration difference of free TRP and plotted these data against our arterial free TRP data (Fig. 1). 74), which is statistically significant (P < 0.0005).