I reckon I have found the answer – the ‘back of legs’ thing definitely comes on when carrying a heavy weight on my back and possibly during some of my weighted exercises.  I found that walking 2 miles to the station from my son’s house, carrying my backpack on my front, did not cause any discomfort. I did not have it at all for the race today.  My other medical thing was hearing loss/dizziness/nausea mid-week and I have an appointment on Tuesday to check.  It only lasted a few hours and I’ve had it before (?? Meniere’s disease? – not sure and should not self-diagnose!) Anyway, overall I’m feeling fit and fine and fingers crossed that will last for HHM unlike the last two years.