Hoping your rest day is a good one,
@roamingpaddy. I am not intending to give medical advice, but in my experience you are likely to be able to nip it in the bud. Starting to stretch the calf muscles the instant that tendonitis/shin splints begins to make its appearance, along with icing the shins, elevation at night, has worked magic for me. I stop right where I am at the first sign of pain, do several good stretches using a tree or a bench or whatever I have nearby. Then a bit of rest, and on I go.
I think the problem is that so much of the terrain of the popular caminos is now on asphalt/tarmac/pavement, that it’s the repetitive foot pounding that messes with our feet. On dirt or other uneven terrain, the foot strike is much less identical, leading to happier feet.
I know that I should do a whole regular series of muscle stretches before starrting to walk, but I usually don’t. What I do do though is start focused stretches at the very first sign of muscle distress, whether it be my quads, my hamstring, my achilles.