There has been a revolution in the measurement of health and fitness writes Dominic Howard. Next time you are in a crowd of people, consider looking at their wrists. It’s likely some will be wearing outsized digital watches, while others will be sporting, some would say, oddly unattractive rubberised bracelets. No, you have not walked into a Trekkie convention. Those innocuous bands are ‘wearables’, all set to be the market’s next great disrupter