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.
There may be a real physiological relationships amongst the details out-of attract, however, a mathematical techniques also can mediate the relationship
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 good spurious relationship ranging from a couple of details is described as one which could occur on lack of people real all-natural outcomes of the newest details (4). The fresh details which were coordinated because of the Nybo et al. (3) commonly separate, irrespective of any physiological elements which can be hypothesized so you’re able to hook up him or her with her. Arterial 100 % free TRP is one changeable regarding the data, it was also active in the site web de rencontre pour polyamoureux calculation of your own almost every other varying to-be coordinated against they (arteriovenous focus improvement off totally free TRP). Ergo, the two variables that were correlated are already connected mathematically, and you may a life threatening moderate-to-large correlation anywhere between both of these variables was expected having any viewpoints off arterial and venous free TRP. This artifact could have been recognized for decades (4) and is recently been shown to be establish by Atkinson ainsi que al. (1) in a number of research studies for the cycling show. We could establish brand new relevancy associated with artifact on the analysis out-of Nybo ainsi que al. (3) with a document simulator.
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).