If young adults stop using a limb for two weeks and then do eight weeks of strength training, their muscle fibers get bigger and gain more blood supply.

What we've found so far is that resistance training after a period of limb disuse appears to increase both muscle fiber size and capillary number in young adults. Our analysis of the available evidence currently supports this idea. We looked at the research and found 38.0 assertions supporting the idea that when young adults stop using a limb for about two weeks and then begin eight weeks of strength training, their muscles respond by growing larger and developing more blood supply [1]. This increased blood supply suggests an increase in capillary number, which helps deliver oxygen and nutrients to the muscle. We did not find any studies that refute this pattern. Our current analysis shows the evidence leans toward a positive effect of resistance training on both muscle structure and vascular support after short-term disuse. While the data we’ve reviewed so far consistently points in this direction, we recognize that science evolves and new findings could refine our understanding over time. It’s important to note that all the evidence we’ve reviewed so far comes from studies involving young adults. We can’t say from this data how other age groups might respond. Practical takeaway: If you’re young and have taken a short break from using a limb—like after an injury or immobilization—getting back into strength training may help rebuild muscle size and improve blood flow to the area. The evidence we’ve reviewed suggests this recovery is possible with consistent effort.