Inactivation of human muscle Na<sup>+</sup>-K<sup>+</sup>-ATPase in vitro during prolonged exercise is increased with hypoxia
Bibliographic record
Abstract
This study investigated the effects of prolonged exercise performed in normoxia (N) and hypoxia (H) on neuromuscular fatigue, membrane excitability, and Na+-K+ -ATPase activity in working muscle. Ten untrained volunteers [peak oxygen consumption (Vo2peak) = 42.1 +/- 2.8 (SE) ml x kg(-1) x min(-1)] performed 90 min of cycling during N (inspired oxygen fraction = 0.21) and during H (inspired oxygen fraction = 0.14) at approximately 50% of normoxic Vo2peak. During N, 3-O-methylfluorescein phosphatase activity (nmol x mg protein(-1) x h(-1)) in vastus lateralis, used as a measure of Na+-K+-ATPase activity, decreased (P < 0.05) by 21% at 30 min of exercise compared with rest (101 +/- 53 vs. 79.6 +/- 4.3) with no further reductions observed at 90 min (72.8 +/- 8.0). During H, similar reductions (P < 0.05) were observed during the first 30 min (90.8 +/- 5.3 vs. 79.0 +/- 6.3) followed by further reductions (P < 0.05) at 90 min (50.5 +/- 3.9). Exercise in N resulted in reductions (P < 0.05) in both quadriceps maximal voluntary contractile force (MVC; 633 +/- 50 vs. 477 +/- 67 N) and force at low frequencies of stimulation, namely 10 Hz (142 +/- 16 vs. 86.7 +/- 10 N) and 20 Hz (283 +/- 32 vs. 236 +/- 31 N). No changes were observed in the amplitude, duration, and area of the muscle compound action potential (M wave). Exercise in H was without additional effect in altering MVC, low-frequency force, and M-wave properties. It is concluded that, although exercise in H resulted in a greater inactivation of Na+-K+-ATPase activity compared with N, neuromuscular fatigue and membrane excitability are not differentially altered.
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How this classification was reachedexpand
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 | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.002 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| 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 itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, 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".