Improved Matching of Local O2 Delivery to Muscle VO2 is Related to Faster VO2 Kinetics
Bibliographic record
Abstract
Improving the matching of local blood flow (Qm) to muscle O2 uptake (VO2m) is thought to be an important factor regulating the adjustment of Phase II pulmonary VO2 kinetics (tauVO2p). The degree to which Qm and VO2m are matched can be discerned from the ratio of changes in muscle deoxygenation ([HHb])-to-phase II VO2p. PURPOSE: To determine the relationship between [HHb]/VO2 and the rate of adjustment of VO2p in subjects presenting with slow and fast VO2p kinetics. METHODS: VO2p and muscle deoxygenation kinetics were examined during repeated step transitions from 20 W to moderate-intensity cycling (80-90% of estimated lactate threshold) in 37 young males (24 (4) yr; mean (±SD)). VO2p was measured breath-by-breath using a volume turbine and a mass spectrometer. Changes in [HHb] of the vastus lateralis muscle were measured by near-infrared spectroscopy. VO2p and [HHb] response profiles were modeled as a mono-exponential using non-linear regression, and later scaled to a relative % of the response (0-100%). The [HHb]-to-VO2 ratio for each individual was calculated as the average [HHb]/VO2 relative response from 20s to 120s during the exercise on-transient. RESULTS: Subjects were grouped based on tauVO2p <21s (very fast (VF); n=8); 21-30s (fast (F); n=12); 31-40s (moderate (M); n=10); >41s (slow (S); n=7). The corresponding [HHb]/VO2 were 0.98 (VF), 1.05 (F), 1.09 (M), and 1.22 (S). The larger [HHb]/VO2 observed in the groups with the slower rates of adjustment for VO2p resulted in the [HHb]/VO2 displaying a transient "overshoot" relative to the subsequent steady state level. That "overshoot" was progressively reduced as tauVO2 became smaller with a correlation between [HHb]/VO2 and tauVO2p of 0.91. CONCLUSION: When tauVO2p is greater than ∼20s, the rate of adjustment of phase 2 VO2p (muscle VO2) appears to be mainly constrained by the matching of local O2 delivery to muscle VO2 (i.e., microvascular blood flow distribution). In those with a shorter tauVO2 there is a reduced "overshoot" in the [HHb]/VO2 as represented by a lower [HHb]/VO2 ratio. These data experimentally support the idea that groups with progressively slower VO2 kinetics are O2 availability dependent, requiring a progressively greater O2 extraction during the on-transient of exercise.
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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) | 0.002 | 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".