Is flexibility a measure of strength?

This blog post is an answer to a question sent to my inbox. If you have a question you'd like answered, please get in touch using the Contact Form, or by sending an email to dan(at)flexibilityresearch(dot)com.

Question: I keep seeing ads for a mobility program in which the young coach says you can't increase flexibility if you don't strengthen the muscles. Is this correct? - Rachel Dunaway

No. Flexibility is the range you have in your joints; strength is how much force you can produce with your muscles. They're distinct, but they influence one another. You express strength only within your flexibility's boundaries, and strength itself can, indeed, enhance flexibility.

Strength training improves flexibility in four ways: firstly, it temporarily suppresses your stretch reflex sensitivity; secondly, it reduces your perception of pain; thirdly, it physically extends muscle fibres through sarcomerogenesis (primarily eccentric training); and finally, it builds a psychological trust, thereby reducing your subconscious fear when holding challenging positions, like splits.

But strength training isn't universally effective. Often, the biggest barriers are pain sensitivity and passive stiffness. We're still learning how pain actually works. For some, strength training can heighten discomfort during stretching. Passive stiffness (the natural resistance to stretch found in all tissues) also presents challenges. Strength training often raises stiffness levels, potentially reducing flexibility for those already predisposed.

The notion that flexibility can't improve without strength training simply isn't true. Among the most robust findings in research is the effectiveness of static passive stretching to enhance flexibility. Is strength beneficial? Usually, yes. But beware: those insisting you absolutely need strength exercises to improve range of motion are telling you something that isn't true, and they're often marketing questionable training programs.

Yours in flexibility,

Dan