THE EFFECTS OF DIET INDUCED OBESITY ON THE FORCE-LENGTH RELATIONSHIP IN RAT SOLEUS
Bibliographic record
Abstract
INTRODUCTION Obesity is associated with chronic inflammation, which has been shown to affect the integrity of musculoskeletal tissues [1]. Previous data from our group suggests that obesity can result in intramuscular fat deposition [1]. It is unclear if this structural alteration has functional consequences, as the implications of obesity on muscle mechanics are not well understood. Therefore, the purpose of this study was to quantify the active force produced by soleus muscles of obese and non-obese rats at a range of muscle lengths. As the inclusion of fat into the muscle fibers will leave less room for contractile proteins, we hypothesized that obese rats will produce lower forces normalized to muscle mass at every length than non-obese control rats. METHODS Fourteen rats were randomly allocated to a 12-week diet: either an obesity-inducing high fat high sucrose diet (DIO, 40% fat, 45% sucrose, n=8) or a standard chow diet (chow, 12% fat 0% sucrose, n=6). Prior to surgery, body composition was evaluated using dual energy X-ray absorptiometry. Custom-made tibial nerve cuffs were surgically attached to the right tibial nerve of each animal. The soleus was exposed, mechanically isolated, and clamped to a force transducer. The muscle was then stretched to a predetermined length and electrically stimulated at 3 times the motor unit threshold (50Hz) and the force output was measured [3]. Force tracings were digitized using WINDAQ® software. Passive, active, and total forces produced by the soleus were normalized to the maximum in vivo length of each animal. Forces were averaged into 5% length intervals within each animal. Students t-tests or a two-way ANOVA were conducted between groups, and a Bonferroni correction was used as needed, α=0.05. RESULTS DIO rats had increased body mass (DIO 816.4 ± 30.1g, chow 645.0 ± 28.3g; p<0.05) and body fat (DIO 39.2 ± 1.3%, chow 21.8 ± 2.1%; p<0.05) compared to chow-fed rats. Soleus mass (DIO: 0.28 ± 0.01 g, chow: 0.26 ± 0.11 g, p=0.32), was similar between the two groups. Absolute peak isometric force was similar between the two groups (DIO: 2.58 ± 0.10 N, chow: 2.18 ± 0.34 N, p=0.23). Active isometric force normalized to soleus mass was significantly higher in DIO group rats at every muscle length ( Figure 1, p<0.05). DISCUSSION AND CONCLUSIONS On average, DIO rats produced more active force at a given normalized length and soleus mass than chow rats, a finding that refutes our original hypothesis. Since optimal length occurs at the same relative muscle length for both groups, and since the decline in force from maximum is similar between groups, it appears that fascicle length, and an associated shift in the force-length relationship cannot explain our results. Results of differences in the force-velocity relationship (not shown here) suggest that the DIO rats may have a higher proportion of fast twitch fibres, but the relative force among slow and fast fibres is similar, and thus also should not affect these results. The results suggest that the force per cross-sectional area is higher in muscles from obese compared to lean rats, a finding that defies explanation at this time and needs thorough investigation in the future. Histology and tests looking at fibre and cell level muscle structures may provide more insight.
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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 | 0.000 |
| 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) | 0.002 | 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".