Sarcomere length non-uniformities dictate force production along the descending limb of the force-length relation
Bibliographic record
Abstract
The force-length relation is one of the most defining features of the sliding filament theory of muscle contraction, and yet a topic of debate in the literature. The force-length relation predicts that the force produced by muscle fibers is directly proportional to the degree of overlap between myosin and actin filaments, but several studies have shown forces that are larger than predicted, especially at long sarcomere lengths. The reason for such discrepancies may be due to technical difficulties – studies have been conducted with muscle fibers, a preparation containing thousands of sarcomeres that makes accurate length measurements challanging. The aim of this study was to directly evaluate force production and sarcomere dynamics in isolated myofibrils and single sarcomeres to enhance our understanding about mechanisms governing deviations from the theoretically predicted force-length relation. Contractions at varying sarcomere lengths (SLs) along the plateau (SL=2.25m-2.39m) and the descending limb (SL>2.39m) of the force-length relation were induced by solution switching, and different modes of force measurements were used. Our results show that single sarcomeres and extrapolated forces resemble the theoretical force-length relation closely, while myofibrils with sarcomere length dispersions show an extension of the plateau region and forces elevated above predicted levels. We also found an increase in sarcomere length non-uniformity and slowed rate of force production at long lengths in myofibrils with sarcomeres in series but not in single sarcomere preparations. We conclude that the deviation of the descending limb of the force-length relation obtained from plateau forces is correlated with the degree of sarcomere length non-uniformity and slowed force development.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
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 | 0.000 |
| 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) | 0.001 | 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".