Lying awake last night it all became clear to me.
The morning after our "templing" in Siem Reap my thighs were sore with all the scrambling up and down deep roughly hewn steps. That day I went for my Japanese massage. The next morning - no sore thighs. So, there was gain from the pain.
Yesterday morning I woke up with sore thighs again. Why? Don't know. Or didn't until 4.30 this morning. It was hunkering through the tunnel at Cu Chi. Still sore this morning but not sore enough to merit the pain of another Japanese massage! I'll just need to get fitter.