At your last vis­it to the doc­tor, you may have re­ceived one of the most im­por­tant pre­scrip­tions of your life, one that on­ly you can fill at a nom­i­nal cost: ex­er­cise. Or as lock­down re­stric­tions have eased, you have de­cid­ed to ac­com­plish one of your New Year res­o­lu­tions, in­tro­duc­ing an ex­er­cise regime.