When young adults stop using a limb for 2 weeks and then do 8 weeks of strength training, their muscles show signs of rebuilding blood vessels—even if they’ve never trained before.

What we've found so far is that after two weeks of not using a limb, followed by eight weeks of resistance training, young adults’ muscles show signs of rebuilding blood vessels [1]. Our analysis of the available research suggests this occurs even in people who have never done strength training before [1]. We looked at one key assertion from the evidence, which is supported by 38.0 studies and not contradicted by any [1]. This means the data we’ve reviewed leans toward the idea that blood vessel markers in muscle tissue begin to recover or grow after a period of disuse, as long as resistance training is resumed for eight weeks [1]. We don’t yet know how strong this effect is, or how it might vary between individuals, because our current analysis is based on limited types of evidence. It’s important to note that we are not saying this process definitely happens in all cases or that it leads to better circulation or performance. We’re only reporting what the current data shows about markers linked to blood vessel growth in muscle [1]. These markers suggest the body is working to restore or build new blood supply to the muscle after it’s been inactive and then retrained. Our current analysis shows a clear pattern in the direction of the evidence, but we also recognize that more research could change or refine what we understand. We don’t have enough information yet to say how long these changes last, or whether they happen the same way in older adults or people with health conditions. Practical takeaway: If you’ve taken time off from using a limb, getting back into strength training may help your muscles rebuild their internal support systems, including the tiny vessels that deliver blood. The evidence we’ve reviewed so far points in that direction.