but he is right: no one is using the syntax and style of a law of the physical world.
so if you want an injury related law you may want to try something like this:
For every great run which leaves you feeling awesome, there is an equal and opposite injury waiting to happen.
Dont forget the originals:
MURPHY'S LAWS
1) If anything can go wrong, it will (and at the worst possible moment).
2) Nothing is as easy as it looks.
3) Everything takes longer than you think it will.
MURPHY'S FOURTH LAW
If there is a possibility of several things going wrong, the one that will cause the most damage will be the one to go wrong.
and of course, my favorites:
GOLD'S LAW
If the shoe fits, it's ugly.
and
COLE'S LAW
Thinly sliced cabbage.