Age-related differences in the loss and recovery of serial sarcomere number following disuse atrophy in rats
Why this work is in the frame
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Bibliographic record
Abstract
BACKGROUND: Older adults exhibit a slower recovery of muscle mass following disuse atrophy than young adults. At a smaller scale, muscle fibre cross-sectional area (i.e., sarcomeres in parallel) exhibits this same pattern. Less is known, however, about age-related differences in the recovery of muscle fibre length, driven by increases in serial sarcomere number (SSN), following disuse. The purpose of this study was to investigate age-related differences in SSN adaptations and muscle mechanical function during and following muscle immobilization. We hypothesized that older adult rats would experience a similar magnitude of SSN loss during immobilization, however, take longer to recover SSN than young following cast removal, which would limit the recovery of muscle mechanical function. METHODS: We casted the plantar flexors of young (8 months) and old (32 months) male rats in a shortened position for 2 weeks, and assessed recovery during 4 weeks of voluntary ambulation. Following sacrifice, legs were fixed in formalin for measurement of soleus SSN and physiological cross-sectional area (PCSA) with the un-casted soleus acting as a control. Ultrasonographic measurements of pennation angle (PA) and muscle thickness (MT) were conducted weekly. In-vivo active and passive torque-angle relationships were constructed pre-cast, post-cast, and following 4 weeks of recovery. RESULTS: From pre- to post-cast, young and older adult rats experienced similar decreases in SSN (-20%, P < 0.001), muscle wet weight (-25%, P < 0.001), MT (-30%), PA (-15%, P < 0.001), and maximum isometric torque (-40%, P < 0.001), but there was a greater increase in passive torque in older (+ 180%, P < 0.001) compared to young adult rats (+ 68%, P = 0.006). Following cast removal, young exhibited quicker recovery of SSN and MT than old, but SSN recovered sooner than PA and MT in both young and old. PCSA nearly recovered and active torque fully recovered in young adult rats, whereas in older adult rats these remained unrecovered at ∼ 75%. CONCLUSIONS: This study showed that older adult rats retain a better ability to recover longitudinal compared to parallel muscle morphology following cast removal, making SSN a highly adaptable target for improving muscle function in elderly populations early on during rehabilitation.
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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 | 0.000 | 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 it