Circulating Free-Tryptophan To Tyrosine As A Marker Of Central Fatigue During Heat Stress
Bibliographic record
Abstract
One theory of central fatigue during exertional heat stress involves the influence on central nervous system activation of the changing ratio of serotonin and dopamine in key thermoregulatory centres in the brain. Circulating concentrations of the precursors, free-tryptophan (f-TRP) and tyrosine (TYR), respectively, compete for the same active carrier across the blood-brain-barrier. Thus, changes in the circulating ratio of f-TRP/TYR may be indicative of changing neurotransmitters in the brain and may help explain the different thermotolerance between endurance trained (TR) and untrained (UT). PURPOSE: The purpose was to examine the use of f-TRP/TYR as an indicator of impending fatigue in TR and UT males during acute uncompensable heat stress to exhaustion (EXH). METHODS: Twelve TR and eleven UT (Mean±SE: VO2peak= 70±2 and 50±1 mL·kgLBM-1·min-1, 11±1 and 16±1% fat, respectively) walked to EXH (Tre= 39.7 and 39.0°C, respectively) on a treadmill (4.5 km·h-1, 2% grade) in 40°C and 30% R.H., wearing combat clothing and a protective hooded overgarment. Before and at a Tre of 38.0, 38.5, 39.0°C, and EXH, venous blood samples were obtained. Serum was analyzed for prolactin (PRL) using a chemiluminescent immunoassay, and plasma analyzed for f-TRP and TYR using gas chromatography/mass spectrometry. RESULTS: TR tolerated a higher Tre (39.7 ± 0.1°C) than the UT (39.0 ± 0.1°C). TYR remained unchanged throughout the heat stress and was not different between groups at baseline (65 ± 3 and 68 ± 6 μM for TR and UT, respectively) or EXH (64 ± 3 and 65 ± 3 μM for TR and UT, respectively). In contrast, f-TRP was higher to a Tre of 39.0°C for TR but thereafter fell significantly to EXH where values were similar between groups (5.7 ± 0.5 and 5.5 ± 0.3 μM for TR and UT, respectively). As a result, f-TRP/TYR was higher for TR (0.11 ± 0.01) vs UT (0.09 ± 0.01) to a Tre of 39.0°C but decreased significantly thereafter for TR to EXH where values were similar for TR (0.09 ± 0.01) vs UT (0.09 ± 0.01). f-TRP/TYR was not related to the increase in PRL which tracked the change in Tre for both groups. Also, there was no relationship between f-TRP/TYR and PRL at EXH (r = 0.17, p > 0.05). CONCLUSION: Circulating TYR and f-TRP/TYR ratio are not sensitive markers of impending fatigue for TR and UT during exertional heat stress. Funded by a Defence R&D Canada Technology Investment Fund.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".