Muscle Recovery After Inactivity Blog Banner
Time off happens. Whether it’s due to injury, illness, a holiday gone on too long, or just life getting in the way, even the most motivated clients (and coaches) sometimes end up skipping training. What comes next? Usually, a slightly panicked look at the mirror or the squat rack, followed by questions like, “How much muscle have I lost?”, “Will I bounce back?” or “Is my body ruined?”
As personal trainers or strength and conditioning coaches, we’ve all had that conversation. And thanks to a recent study by McIntosh and colleagues (2025), we’ve now got some new science to back up our answers. In particular, when it comes to how the vascular system inside muscle responds to disuse and how resistance training can bring it back online.
This research adds an important layer to what we already know about rebuilding muscle mass. It shows that recovery after time off is about what’s happening at the level of capillaries and angiogenic signalling, not just muscle size or strength. And the good news? Your clients can bounce back, whether they’re seasoned lifters or complete novices.
And if you’re the kind of coach who loves to stay on top of new research or if you’re currently digging into on of our PT or personal training courses, this one’s definitely worth your time.
Researchers from Auburn University took a group of young adults, some with a history of regular resistance training and others without, and immobilised one of their legs for two weeks using a locked brace. After this period of forced disuse, participants jumped into an eight-week supervised resistance training programme designed to bring that leg back to full function.
Throughout the process, the researchers took muscle biopsies from the vastus lateralis, part of the quadricep group of muscles, to measure changes in:
Why all the fuss about capillaries and growth factors? Because angiogenesis, that is the formation of new blood vessels, is a key part of muscle adaptation and it plays a bigger role than we often give it credit for.
After just two weeks of immobilisation, things had already started to shift at the molecular level. The researchers found that levels of VEGF (vascular endothelial growth factor), a protein that kickstarts new capillary growth, had dropped significantly. At the same time, TSP-1, which acts like a brake on angiogenesis, went up. It was an anti-growth signal, biologically speaking.
Surprisingly though, actual capillary number didn’t decline during those two weeks. That’s a big deal. It suggests that the vascular system in skeletal muscle is quite resilient, at least over short periods, even when the signalling environment takes a turn for the worse. In other words, the muscle prepares to shrink, but doesn’t fully commit yet.
This mirrors what we know from previous research. For example, studies on bed rest and step-reduction have shown that capillary rarefaction (loss) is a slower process compared to muscle size or metabolic shifts (Hendrickse et al., 2022). But when the molecular markers change, it’s a warning that sets the stage for faster atrophy if inactivity continues.
After eight weeks of resistance training however, the negative trends reversed.
These capillaries are vital. They support oxygen delivery, nutrient transport and waste removal in the muscle. These are all things that influence endurance, recovery and ultimately training quality. If you’ve ever worked with a powerlifter who burns out too early in a volume block, or an athlete struggling with repeat sprint fatigue, these microvascular changes could be part of the explanation.
What is even more interesting is that muscle fibre size also bounced back. Type II fibre cross-sectional area increased by 25% from the post-disuse low point, demonstrating a strong hypertrophic response over just eight weeks. But here’s the twist. The study found no strong correlation between capillary growth and muscle size changes in these young adults.
That doesn’t mean capillaries don’t matter. It just means that in young, healthy people, capillary number might not be the limiting factor for hypertrophy, at least not in the short term. In older adults or those with metabolic issues, it’s a different story. Research from Snijders et al. (2017) and Moro et al. (2019) shows that low capillarisation can actually blunt the hypertrophic response to training in those populations.
So, what can you do with all this information? Quite a bit, actually.
First, if your client is returning from time off due to surgery, illness, burnout or any other reason, you can reassure them with confidence that muscle and its vascular support systems are highly adaptable. Just two months of targeted RT can reverse disuse effects at both the fibre and molecular level.
Second, you don’t have to overthink a client’s training history. Trained and untrained participants in this study responded similarly to the disuse and re-training protocol. So if you’re working with an ex-athlete or a total beginner, a smart, progressive training plan will still do the trick.
Third, think beyond just size and strength. If you’re coaching athletes in team sports, combat sports, or anything that involves high work rates, capillarisation plays a key role in performance. More capillaries mean better oxygen delivery, quicker recovery between efforts and less fatigue. All of this is supported by resistance training.
And finally, it’s a reminder that even short periods of inactivity can kick off changes at the cellular level. You might not see muscle loss immediately, but the body starts shifting gears internally. That’s why a structured return to training and not a YOLO leg day, is the smarter approach.
Muscle recovery after disuse is about restoring the infrastructure that keeps muscles functioning at their best. The capillaries, the enzymes, the growth factors. They are all part of the comeback story.
This study by McIntosh et al. (2025) gives strength and conditioning coaches and personal trainers more than just reassurance. It offers a clear roadmap and shows that two weeks of disuse isn’t the end of the world, and eight weeks of smart resistance training is enough to turn things around both inside and out.
It doesn’t matter if you’re guiding a weekend warrior through post-surgery recovery or helping a pro athlete return to form after a layoff, understanding these underlying processes adds depth to your programming and clarity to your coaching.
Do you have an interest in designing programmes that get results after injury, time off or detraining? On our Strength & Conditioning Exercise Specialist & Master Diplomas, you’ll learn how to rebuild strength, size and performance with proven strategies backed by the latest research. A 2025 study showed that just two weeks of immobilisation can significantly reduce key muscle growth signals like VEGF, but eight weeks of resistance training restored them, as well as increased type II muscle fibre size by 25%. It doesn’t matter if your clients are athletes, weekend warriors or returning gym-goers, this course gives you the tools to help them come back stronger, faster and more resilient.
Strength & Conditioning Exercise Specialist & Master Diploma™ – In-Person, Live-Virtual & Distance Study
Already a qualified PT and ready to push further? Our Level 4 Strength & Conditioning Coaching course is your next step towards becoming an S&C specialist. Designed for experienced personal trainers, this course builds on your existing knowledge and prepares you to coach athletes and high-performing clients with confidence. You’ll dive into advanced training methods, periodisation and performance analysis. There are exactly the skills you need to stand out as a personal trainer. If you’re looking to work with sports teams or want to step your one-to-one coaching up a notch, this is the recognised pathway to becoming a fully qualified strength & conditioning coach.
Strength & Conditioning Coaches Course – Distance Study
Rethinking Post-Workout Recovery You can’t miss them on the shelves. Those flashy bottles promising faster…
We all know stretching’s good for mobility and flexibility. But did you know a recent…
We all know that lifting weights builds stronger muscles, improves posture and helps with fat…
A PT’s Guide to Dosing for Performance If you’ve been going to the gym for…
We’ve all seen it, clients buzzing with excitement because they’ve finally shifted a few kilos.…
When we talk about resistance training, most people picture barbells, protein shakes and twenty-somethings flexing…