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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 bona fide psychological dating involving the variables away from interest, but an analytical techniques can also mediate the connection
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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Good spurious correlation ranging from one or two variables is understood to be one which might happen throughout the absence of any actual natural link between new parameters (4). The brand new variables that have been coordinated by the Nybo mais aussi al. (3) commonly separate, aside from people emotional systems which might be hypothesized so you’re able to hook him or her together. Arterial totally free TRP is actually one to varying on the research, nonetheless it was also active in the calculation of your almost every other adjustable becoming coordinated against they (arteriovenous attention variation regarding heiÃŸes NÃ¼chtern-Dating 100 % free TRP). Hence, the two variables that were correlated are usually connected mathematically, and you may a life threatening average-to-large relationship between both of these parameters could well be asked with one viewpoints of arterial and you can venous totally free TRP. This artifact could have been noted for many years (4) and you may try recently proven to be present of the Atkinson mais aussi al. (1) in a few research studies to your bicycling performance. We could prove brand new relevancy with the artifact into the research regarding Nybo ainsi que al. (3) by using a data 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).