Strength actually makes you flexible: Mobility Training & Joint Health

To me it seemed like for a long time, the fitness world always drew this line between two types of people: those who lift weights and those who stretch and do yoga. Flexibility was seen as a "yoga thing" — something “strong people” struggled with. Finally a new large-scale scientific review shows that this is not true and things are not black & white.

The Finding That Changes Things

Researchers looked at decades of studies and found that strength training significantly improves joint flexibility — often just as well as regular stretching. But the most interesting part is: the biggest improvements didn't come from people simply moving through a range of motion. They came when people were actively engaging their own muscles with real effort —> so using their own “inner strength” while moving.

So it’s not only about external weight. It’s about the internal strength effort — the internal tension of a muscle working hard, especially at the end of its range.

Side note from me: This Is What FRC Is - an Internal Strength Training

Functional Range Conditioning (FRC) and similar mobility systems are not really about lifting weights. They are about generating force from within: using your own muscles to contract, or actively push and pull into positions. The PAILs and RAILs contractions, the slow controlled rotations, the end-range holds where you squeeze as hard as you can — all of this is asking your body to work hard from a stretched position. This also increases range of motion (ROM) in a more efficient/fast way than passive stretching.

What the research suggests is that this kind of active effort is exactly what creates faster, lasting change in your flexibility. The body doesn't adapt much to just being stretched. It adapts to being challenged — and your own internal effort counts as a challenge.

This also helps explain something many people have noticed: passive stretching alone — holding pigeon pose, lying in a strap stretch, sitting in a split — often doesn't create much lasting change. Of course, over a long period of time there will be improvements, but adding strength training shows improvements way faster. If there's no muscular effort involved, the signal to the body to adapt the tissue is simply not strong enough.

Long-Term Joint Health

The research also touches on something important for anyone thinking about staying mobile as they get older. As we age, connective tissue naturally becomes stiffer. But active exercise — especially when muscles and tendons are working at their longer, stretched-out positions — seems to slow that process down. The tissues stay more elastic and responsive.

This supports what many movement coaches argue: joints need to be used with effort, not just gently moved or, worse, avoided altogether.

The Simple Takeaway

No matter where you come from; weightlifting, yoga or functional mobility work, the research points to the same thing: passive flexibility is not enough. What actually changes the body is effort at end range. That's what tells your nervous system and your connective tissue to adapt and that a new range of motion is possible and safe to use.

Stretching is not a passive act. Or at least, it really shouldn't be.

Read the study here: https://pubmed.ncbi.nlm.nih.gov/39787531/
Favro et al. (2025). "The Influence of Resistance Training on Joint Flexibility in Healthy Adults: A Systematic Review, Meta-analysis, and Meta-regression." Journal of Strength and Conditioning Research.