Dynamics of intramuscular<sup>31</sup>P-MRS P<sub>i</sub>peak splitting and the slow components of PCr and O<sub>2</sub>uptake during exercise
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Bibliographic record
Abstract
The dynamics of pulmonary O(2) uptake (Vo(2)) during the on-transient of high-intensity exercise depart from monoexponentiality as a result of a "slow component" whose mechanisms remain conjectural. Progressive recruitment of glycolytic muscle fibers, with slow O(2) utilization kinetics and low efficiency, has, however, been suggested as a mechanism. The demonstration of high- and low-pH components of the exercising skeletal muscle (31)P magnetic resonance (MR) spectrum [inorganic phosphate (P(i)) peak] at high work rates (thought to be reflective of differences between oxidative and glycolytic muscle fibers) is also consistent with this conjecture. We therefore investigated the dynamics of Vo(2) (using a turbine and mass spectrometry) and intramuscular ATP, phosphocreatine (PCr), and P(i) concentrations and pH, estimated from the (31)P MR spectrum. Eleven healthy men performed prone square-wave high-intensity knee extensor exercise in the bore of a whole body MR spectrometer. A Vo(2) slow component of magnitude 15.9 +/- 6.9% of the phase II amplitude was accompanied by a similar response (11.9 +/- 7.1%) in PCr concentration. Only five subjects demonstrated a discernable splitting of the P(i) peak, however, which began from between 35 and 235 s after exercise onset and continued until cessation. As such, the dynamics of the pH distribution in intramuscular compartments did not consistently reflect the temporal features of the Vo(2) slow component, suggesting that P(i) splitting does not uniquely reflect the activity of oxidative or glycolytic muscle fibers per se.
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Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.002 | 0.001 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| 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 it