Muscle knots. Sigh.
First let's say this and get it out of the way: There is no such thing as a muscle knot.
There is no such thing as a muscle knot.
The idea that certain fibers in a muscle can become "knotted" or "stuck" and that we, manual therapist, can, with our bare hands, unstick them or rub out the knot, is not supported by any study or model of anatomy that I've seen. There is no correlating pathology in the medical community that means "muscle knot".
So what are people talking about when they say "knot"? It's usually either a lumpy or bumpy muscle they've run across and can't identify it. There are a few common areas people have "knots" that just end up being a tendon or edge of a muscle that can feel bumpy. You've got lots of bumpy muscles and tendons in your body, but when these are correlated with the areas of pain or tightness you're experiencing, this can lead your brain to want to identify a physical object that must be what's causing all this. Pain is not so simple unfortunately.
Some therapists use the word "knot" to mean "trigger point". Trigger Point Theory says you have areas of hyper contracted fibers inside bigger muscles, and that these can refer pain to other areas. There is a lot of anecdotal evidence in the patterns, but the actual methodology has mixed scientific reports, the biggest issue being that even people who touch bodies for a living have about a 50/50 chance of correctly palpating areas of anatomy (https://www.ncbi.nlm.nih.gov/pubmed/19158550), which would make it very difficult to correctly palpate a small area of contraction. There's studies and reports about wishful-thinking palpating and examining and how that works in our brains, but maybe that's a different blog post. Here's a great article that gets into Trigger Point Theory: https://www.painscience.com/articles/trigger-point-doubts.php
What do I hear when a client tells me they have a muscle knot? Either hey have had a massage in the past where the therapist used that language and they took it and labeled themselves with it, or they feel something bump where there is pain, and that's what word society uses for that phenomenon. It's very easy and understandable, when a person in authority gives you words to describe what is going on with your body, and giving something a name makes it much easier for our brain to process and think up solutions for.
I don't use the word knot. I think it's a fine metaphor for tightness and pain, but I don't find it helpful and feel it could be harmful to pathologize something completely normal. What's more helpful, telling you you have a disease that only I can help get rid of, or that what you're feeling is a totally normal pain pattern your brain has learned, and massage (along with lots of movement based therapies) can help rewire that pattern into something that doesn't cause pain?
I would much rather my clients feel in control of their pain, of their bodies, and learn to love their bodies instead of come to be because their body is "messed up" and they need me to "fix" them. There are plenty of therapists with that mindset. But not in my treatment room. There you are an amazing body with unlimited potential to love and feel the way you want to. I'm just your guide to that.