Impaired sarcoplasmic reticulum Ca<sup>2+</sup> release is the major cause of fatigue‐induced force loss in intact single fibres from human intercostal muscle
Bibliographic record
Abstract
Key points Changes in intramuscular Ca 2+ handling contribute to development of fatigue and disease‐related loss of muscle mass and function. To date, no data on human intact living muscle fibres have been described. We manually dissected intact single fibres from human intercostal muscle and simultaneously measured force and myoplasmic free [Ca 2+ ] at physiological temperature. Based on their fatigue resistance, two distinct groups of fibres were distinguished: fatigue sensitive and fatigue resistant. Force depression in fatigue and during recovery was due to impaired sarcoplasmic reticulum Ca 2+ release in both groups of fibres. Acidification did not affect force production in unfatigued fibres and did not affect fatigue development in fatigue‐resistant fibres. The current study provides novel insight into the mechanisms of fatigue in human intercostal muscle. Abstract Changes in intracellular Ca 2+ handling of individual skeletal muscle fibres cause a force depression following physical activity and are also implicated in disease‐related loss of function. The relation of intracellular Ca 2+ handling with muscle force production and fatigue tolerance is best studied in intact living single fibres that allow continuous measurements of force and myoplasmic free [Ca 2+ ] during repeated contractions. To this end, manual dissections of human intercostal muscle biopsies were performed to isolate intact single fibres. Based on the ability to maintain tetanic force at >40% of the initial value during 500 fatiguing contractions, fibres were classified as either fatigue sensitive or fatigue resistant. Following fatigue all fibres demonstrated a marked reduction in sarcoplasmic reticulum Ca 2+ release, while myofibrillar Ca 2+ sensitivity was either unaltered or increased. In unfatigued fibres, acidosis caused a reduction in myofibrillar Ca 2+ sensitivity that was offset by increased tetanic myoplasmic free [Ca 2+ ] so that force remained unaffected. Acidification did not affect the fatigue tolerance of fatigue‐resistant fibres, whereas uncertainties remain whether or not fatigue‐sensitive fibres were affected. Following fatigue, a prolonged force depression at preferentially low‐frequency stimulation was evident in fatigue‐sensitive fibres and this was caused exclusively by an impaired sarcoplasmic reticulum Ca 2+ release. We conclude that impaired sarcoplasmic reticulum Ca 2+ release is the predominant mechanism of force depression both in the development of, and recovery from, fatigue in human intercostal muscle.
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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) | 0.000 | 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) | 0.000 | 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".