The influence of metabolic and circulatory heterogeneity on the expression of pulmonary oxygen uptake kinetics in humans
Bibliographic record
Abstract
New Findings What is the central question of this study? The finding that pulmonary oxygen uptake ( ) kinetics on transition to moderate exercise is invariant and exponential is consistent with a first‐order reaction controlling . However, slowed kinetics when initiating exercise from raised baseline intensities challenges this notion. What is the main finding and its importance? Here, we demonstrate how a first‐order system can respond with non‐first‐order response dynamics. Data suggest that progressive recruitment of muscle fibre populations having progressively lower mitochondrial density and slower microvascular blood flow kinetics can unify the seemingly contradictory evidence for the control of on transition to exercise. We examined the relationship amongst baseline work rate (WR), phase II pulmonary oxygen uptake ( ) time constant ( ) and functional gain during moderate‐intensity exercise. Transitions were initiated from a constant or variable baseline WR. A validated circulatory model was used to examine the role of heterogeneity in muscle metabolism ( ) and blood flow ( ) in determining kinetics. We hypothesized that andGPwould be invariant in the constant baseline condition but would increase linearly with increased baseline WR. Fourteen men completed three to five repetitions of ∆40 W step transitions initiated from 20, 40, 60, 80, 100 and 120 W on a cycle ergometer. The ∆40 W step transitions from 60, 80, 100 and 120 W were preceded by 6 min of 20 W cycling, from which the progressive ΔWR transitions (constant baseline condition) were examined. The was measured breath by breath using mass spectrometry and a volume turbine. For a given ΔWR, both (22–35 s) andGP(8.7–10.5 ml min−1 W−1) increased (P < 0.05) linearly as a function of baseline WR (20–120 W). The was invariant (P < 0.05) in transitions initiated from 20 W, butGPincreased with ΔWR (P < 0.05). Modelling the summed influence of multiple muscle compartments revealed that could appear fast (24 s), and similar toin vivomeasurements (22 ± 6 s), despite being derived from values with a range of 15–40 s and with a range of 20–45 s, suggesting that within the moderate‐intensity domain phase II kinetics are slowed dependent on the pretransition WR and are strongly influenced by muscle metabolic and circulatory heterogeneity.
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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 | 0.001 | 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 | 0.001 |
| Scholarly communication | 0.001 | 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".