Why does this matter?
As Brooke Thomas writes in her Breaking Muscle article,
“…because they are pliable, you can work quite close to the bones because the rubber will nestle in around the protuberances rather than impinging them. This is good news since you will often get a more dramatic result working at attachment sites of muscles, which are, more often than not, on the bone.”
Imagine you wanted to paint this wall…
Like most walls (and like all body parts), this wall is not completely flat. What kind of tool would you use? What would happen if you tried to paint the textured nooks and crannies of the brick wall with a crusty, hardened paint brush?
My guess is that there would be many unpainted spots, particularly in the smaller, angled crevices that the hardened bristled of the brush couldn’t bend to fit into.
This is also related to size of the object (which I will explain in a future series of articles), but the important thing to remember is that pliability is an advantage when it comes to self-massage because there is great benefit to nestling into the small spaces, in-between muscles, and at the attachment points where muscles connect to bones.
That being said, hard tools are not useless. There are cases where a great amount of mechanical force is required to create change in connective tissue, and a soft object is not always enough to achieve that amount of force. While some of this work can become safe as DIY bodywork with experience, it best to outsource it to an experienced professional, at least at first, until you know what you’re doing.