Physical activity and accelerometer - A triaxial accelerometer (Actigraph GT1M, ActiGraph, LLC) was worn for the four days of the survey period. It was worn on the waist and reported acceleration using a proprietary unit - "counts". An accelerometer diary was also used to track activities that are poorly recorded by accelerometers such as cycling and swimming and to record when the accelerometer was removed e.g. for sleeping/showering.