There was a time when I chose my underwear purely on the way it looked – was it lacy, slinky, flattering, prettily-coloured? Rarely did I think – is this functional?And then naturally I’d spent the next few months surreptitiously hoiking them up, wriggling them down, plucking them out… or simply passing over them in the drawer unless I’m dressing up for a night out. Modal Rich Flexifit™ High Leg Knickers £6, sizes 6 to 28. Then a few years ago I started running, and actually made the exercise habit stick. I say ‘running’ but really I mean jouncing, bouncing...