Prolactin as an Indicator of Impending Fatigue during Uncompensable Exertional Heat Stress
Bibliographic record
Abstract
Changes in circulating prolactin (PRL) concentrations have been suggested as a marker of impending fatigue due to its strong relationship with core temperature (Tre) and the purported interplay between brain serotonergic and dopaminergic activity. Yet, comprehensive examination of PRL between groups with different fitness levels and during repeated exertional heat stress (EHS) has not been reported. PURPOSE: To examine the use of PRL as an indicator of impending fatigue in endurance trained (TR) and untrained (UT) males during acute (Study 1) and repeated (Study 2) EHS. METHODS: Subjects walked to exhaustion (EXH) on a treadmill (4.5 km·h-1, 2% incline) in 40°C wearing combat clothing and a protective hooded overgarment for acute and repeated (9 days over 11 days) sessions. Study 1 included 12 TR and 11 UT (Mean ± SE: VO2peak = 70 ± 2 and 50 ± 1 mL·kgLBM-1·min-1) and study 2 included 9 UT (VO2peak = 51.7 ± 1.9 mL·kgLBM-1·min-1) males. Venous blood samples were obtained at rest (PRE; prior to heat) and at a Tre of 38, 38.5, 39, 39.5, 40°C and/or EXH. PRL was measured by chemiluminescence. RESULTS: In Study 1, the TR tolerated a higher Tre and longer tolerance time (39.7 ± 0.1°C, 165 ± 11 min) than the UT (39.0 ± 0.1°C, 106 ± 10 min). In Study 2, although Tre EXH was not different (p < 0.06) from Day 1 (38.8 ± 0.1°C) to 9 (39.1 ± 0.1°C), time to EXH increased from Days 1 (95 ± 8 min) to 9 (145 ± 13 min). PRL exhibited a strong relationship with increases in Tre, responding to relative thermal strain, in both studies. In Study 1, increases in PRL were directly related to the change in Tre for both the UT and TR, reaching similar values at EXH (55.4 ± 7.2 and 56.7 ± 4.5 ug·L-1, respectively) despite the 0.7°C higher Tre tolerated for TR. Similarly, PRL values at EXH were similar on Days 1 (48.4 ± 7.2 ug·L-1) and 9 (51.1 ± 8.6 ug·L-1) in Study 2. In addition, PRL was moderately correlated to perceptual strain (PeSI) in Study 1 (r = 0.51) and 2 (r = 0.46), which was also similar between groups or days at EXH. CONCLUSION: Findings suggest that as aerobic fitness increases PRL values will reflect the lower PeSI at a given Tre and respond to the relative, rather than the absolute, thermal strain. PRL is an important marker of impending fatigue given its responsiveness to progressive increases in thermal strain. Funded by DRDC Technology Investment Fund and US Office of Naval Research.
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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 | 0.001 |
| 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) | 0.000 | 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".