Taken from Mayo clinic, for anyone not clear on what isometric exercise refers to:
Isometric exercises are tightening (contractions) of a specific muscle or group of muscles. During isometric exercises, the muscle doesn't noticeably change length. The affected joint also doesn't move. Isometric exercises help maintain strength. They can also build strength, but not effectively. And they can be performed anywhere. Examples include a leg lift or plank.
Follow up details - isometric exercises don't have to be just bodyweight, and can be trained for strength by performing the exercise against something to constrain the motion. Imagine crawling under your bed before performing the plank (now more of a pushup, since you're pressing with your chest muscles) mentioned above. You can push as hard as possible, but you won't budge the bed.
They're incredible for returning from injury, since you can specifically train ranges of motion, and the person performing the exercise has full control of the "load" - aka how hard to exert themselves.
I had a watchOS app made (Hold Steady on App Store) for my olympic pistol isometric training if anyone feels like exercising their arms instead. Have no idea if it has a comparable effect on blood pressure though.
Isometric exercises are tightening (contractions) of a specific muscle or group of muscles. During isometric exercises, the muscle doesn't noticeably change length. The affected joint also doesn't move. Isometric exercises help maintain strength. They can also build strength, but not effectively. And they can be performed anywhere. Examples include a leg lift or plank.