Session duration affects the magnitude of post-exercise hypervolemia but not the erythropoietin response to acute high-intensity interval exercise
Bibliographic record
Abstract
ABSTRACT The increase in plasma volume ∼24 hours post-exercise may act as an erythropoietic signal, but this mechanism’s responsiveness to different exercise prescription variables is poorly understood. The purpose of this study was to determine the impact of high-intensity interval exercise duration on plasma volume and related responses. On separate days, 16 healthy, recreationally active participants (n=8 males; n=8 females) performed four (4×4) or eight intervals (8×4) consisting of 4 min at 105% critical power with 3 min recovery. Venous blood samples collected before, immediately after, and 24 hours after each HIIT session were used to measure hemoglobin concentration and hematocrit to calculate plasma volume changes. Erythropoietic and plasma volume regulating hormone concentrations were measured using ELISA kits. Plasma volume decreased immediately after both protocols (4×4: −4.4±3.5%, p<0.05; 8×4: −4.4±3.6%, p<0.05) but was only significantly elevated above baseline 24 hours after the 8×4 protocol (4×4: +1.0±7.1%, p>0.05; 8×4: +5.6±4.6%, p<0.05). Erythropoietin concentration ([EPO]) was higher than baseline 24 hours after the HIIT protocols (4×4: Pre vs 24 h post: 6.5±3.1 vs. 7.1±3.3 mIU/mL; 8×4: 6.9±3.7 vs. 7.3±3.7 mIU/mL; main effect of time, p<0.05) with no difference between protocols (p>0.05). [Aldosterone] was elevated immediately post-exercise after both protocols (4×4: Pre vs 0 h post: 295±151 vs. 544±259 pg/mL; 8×4: 335±235 vs. 821±553 pg/mL), but the 8×4 protocol caused a larger increase (interaction effect, p<0.05). That post-exercise hypervolemia may be exercise duration-dependent but is not required for increases in circulating EPO has important implications for endurance training aiming to increase oxygen delivery to active tissues. NEWS AND NOTEWORTHY This study is the first to show that both a common HIIT protocol length (4 x 4 min) and an extended HIIT protocol (8 x 4 min) similarly increased [erythropoietin] 24 h after exercise, despite only the extended protocol transiently increasing plasma volume. Previous works have investigated plasma volume regulation following different HIIT durations, but not explored links to erythropoietic signalling. This study’s findings have relevance for understanding the physiology of exercise-induced erythropoiesis.
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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) | 0.002 | 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".