Limitations to oxygen transport and utilization during sprint exercise in humans: evidence for a functional reserve in muscle O<sub>2</sub> diffusing capacity
Bibliographic record
Abstract
Key points Severe acute hypoxia reduces sprint performance. Muscle during sprint exercise in normoxia is not limited by O2 delivery, O2 offloading from haemoglobin or structure‐dependent diffusion constraints in the skeletal muscle of young healthy men. A large functional reserve in muscle O2 diffusing capacity exists and remains available at exhaustion during exercise in normoxia; this functional reserve is recruited during exercise in hypoxia. During whole‐body incremental exercise to exhaustion in severe hypoxia, leg is primarily dependent on convective O2 delivery and less limited by diffusion constraints than previously thought. The kinetics of O2 offloading from haemoglobin does not limit in hypoxia. Our results indicate that the limitation to during short sprints resides in mechanisms regulating mitochondrial respiration. Abstract To determine the contribution of convective and diffusive limitations to during exercise in humans, oxygen transport and haemodynamics were measured in 11 men (22 ± 2 years) during incremental (IE) and 30 s all‐out cycling sprints (Wingate test, WgT), in normoxia (Nx, : 143 mmHg) and hypoxia (Hyp, : 73 mmHg). Carboxyhaemoglobin (COHb) was increased to 6–7% before both WgTs to left‐shift the oxyhaemoglobin dissociation curve. Leg was measured by the Fick method and leg blood flow (BF) with thermodilution, and muscle O2 diffusing capacity ( ) was calculated. In the WgT mean power output, leg BF, leg O2 delivery and leg were 7, 5, 28 and 23% lower in Hyp than Nx (P < 0.05); however, peak WgT was higher in Hyp (51.5 ± 9.7) than Nx (20.5 ± 3.0 ml min−1 mmHg−1, P < 0.05). Despite a similar (33.3 ± 2.4 and 34.1 ± 3.3 mmHg), mean capillary (16.7 ± 1.2 and 17.1 ± 1.6 mmHg), and peak perfusion during IE and WgT in Hyp, and leg were 12 and 14% higher, respectively, during WgT than IE in Hyp (both P < 0.05). was insensitive to COHb (COHb: 0.7 vs. 7%, in IE Hyp and WgT Hyp). At exhaustion, the Y equilibration index was well above 1.0 in both conditions, reflecting greater convective than diffusive limitation to the O2 transfer in both Nx and Hyp. In conclusion, muscle during sprint exercise is not limited by O2 delivery, O2 offloading from haemoglobin or structure‐dependent diffusion constraints in the skeletal muscle. These findings reveal a remarkable functional reserve in muscle O2 diffusing capacity.
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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) | 0.001 | 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".