Tension is a Verb

Excess tension is not a noun, a thing. Excess tension is a verb, an action. Excess tension is often thought of as a blockage, like a clog in a pipe but in reality it is more like clenching a fist and holding it. Excess tens-ION is actually excess tens-ING. It's an activity that is happening in the present; an isometric exercising that can over-develop the muscles involved and cause imbalances and a loss of flexibility.

Another important thing to keep in mind is that as an ongoing physical process, tension is supported by an ongoing mental process. Those muscles etc. aren't acting on their own; they are receiving instructions that are generated by the way we use our brain. Therefore, the source of excess tension is excess thinking and the solution is to change the habitual patterns of over-thinking that lead to that over-tensing.