The impact of quadriceps disuse atrophy on motor unit properties
Bibliographic record
Abstract
Disuse atrophy describes the reduction in skeletal muscle mass and strength accompanying periods of inactivity (1). This impairment is of interest in the lower limbs due to their high functional importance in activities of daily living. Similar to the age‐related loss of muscle mass associated with sarcopenia, disuse atrophy has widespread impact throughout the muscle tissue, and whilst mechanisms of muscle atrophy are reasonably well described (2), data on adaptations of the peripheral neuromuscular system are scant. The aim of the current study was to explore neuromuscular changes in individual motor units (MUs) of the vastus lateralis (VL) following 15 days of whole‐leg immobilisation. Intramuscular electromyography (iEMG) was performed in 8 healthy males (18‐25 years) before and after 15 days of unilateral leg immobilisation. Individual MU potentials (MUPs) were sampled from near the VL motor point during isometric contractions held at 25% of maximum voluntary contraction (MVC). MUP complexity was quantified by the number of significant slope changes within the MUP template (turns), and MUP duration as the time in ms between MUP onset and offset. The non‐immobilised limb served as a control. Multi‐level mixed effects linear regression models were used to examine effects of the intervention, with leg and time as factors. Significance was accepted as p<0.05. MVC decreased by 30% in the immobilised leg (p<0.05) with no difference in the control leg (p=0.23). Analysis of the number of MUP turns revealed significant interaction effects between leg and time (p<0.05); the number of MUP turns increased in the immobilised leg (β = 0.442, 95% CI: 0.160 – 0.724, p<0.01), and did not differ in the control leg (p=0.861). Similarly, there was a significant interaction between leg and time point for MUP duration (p<0.05), which was greater post intervention in the immobilised leg (β = 1.349, 95% CI: 0.72 – 1.97, p<0.001), and did not differ in the control leg (p=0.183). The increased MUP complexity and duration in the immobilised leg can be caused by increased electrophysiological temporal dispersion across MU fibres, which in turn can be related to increased differences in conduction times along axonal branches and/or MU fibres. These findings therefore indicate that short‐term immobilisation of large limb muscles can exert notable effects on MU morphology and electrophysiology. Clinical pre‐/rehabilitation regimes targeting disuse atrophy should also aim to specifically target peripheral motor nerves to mitigate the MU changes shown to occur following periods of disuse, potentially facilitating enhanced improvements in functional outcomes. 1. Rudrappa SS et al, J. Front Physiol. 2016;7(AUG):1–10. 2. Brook MS et al, J. Curr Opin Clin Nutr Metab Care. 2017;20(6):433–9.
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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 | 0.001 |
| 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) | 0.002 | 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".