Focusing isn't just an optical activity, it is also a mental one.

Bridget Riley said this. And well she might. I'm not a great fan of her art (at least, the pieces I've seen)  It involves a lot of effort simply to look at it. Bear in mind that I'm a person who feels slightly queasy on a moving walkway if I look down at the striations.

Yep, just looking at that makes my head spin. She's very talented, is Bridget Riley. It MUST be a talent to be able to produce something that has such a profound physical effect on someone. Here's another:

I find myself blinking and squinting just to make some sort of sense of it.

Bizarrely enough, but you must be used to this by now with me, this train of thought was triggered by boxing. Me. And boxing.

Boxercising, I think it's called.

Me, I'm a bit lethal. The exercise was:

1, 2 - jab
3, 4 - hook
5, 6 - uppercut

Tara, with the protective (but not very if you missed) hand pads, would call out the numbers and I was meant to produce the correct punches. Hand-eye coordination...no, hand-eye-BRAIN coordination severely lacking. Oh how we laughed! I'm not sure how much we would have laughed if I'd thwacked her on the jaw and knocked her out. Well, I might have, but she would've been unconscious.

The thing was, exactly as when I look at a Bridget Riley print, I felt instantly disorientated and exhausted. Ten seconds before that,  I'd been quite happily doing crunches and squats and sprints without feeling weary, but THIS...

For sure, for me, tired brain equals tired body.

...at least, the SEMBLANCE of a tired body. Tired body equals tired brain? No.