Division of loading time in reloading the disused atrophic soleus muscle induces proximal muscle injury.
Ryo Miyachi, Yui Morita, Toshiaki Yamazaki
PMID 36866019WHAT IT FOUND
Splitting daily loading into two shorter bouts helped regrow distal soleus muscle fibers in rats but increased signs of muscle damage near the tendon.
Continuous loading appeared safer for the muscle tissue overall, suggesting split sessions may risk injury without proper warm-up.
Key findings
01Dividing loading time into two sessions significantly increased muscle fiber size in the distal region compared to the atrophied group, whereas continuous loading did not.
02The twice-daily loading group showed significantly higher levels of central nuclei fibers in the proximal region, indicating increased muscle damage and regeneration response in that area.
03The authors conclude that continuous loading is preferable to divided loading to prevent muscle injury during the reloading of atrophic muscles.
STILL TO COME
How it was doneWhat they foundWhat it means for PTs
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What it does not show
The study was conducted entirely in rats, so findings do not directly translate to human muscle physiology. The analysis was performed only 7 days after reloading began, so long-term effects on muscle health were not observed. Only the soleus muscle was tested; other muscles may respond differently to divided loading. The study did not test the effect of warm-up or preconditioning, which the authors note might mitigate the observed damage.
Declared interests
Funded by JSPS KAKENHI Grant Number JP 20K11204. The authors declared no conflicts of interest.
The easy way to misread this
Do not apply these findings directly to human patients. This is a rat study with very low certainty for clinical practice. The observed increase in muscle damage markers in the proximal region suggests that dividing loading time might be harmful without preconditioning, but this has not been tested in humans.