I think it'd be great if the hearts were the result of a "fitness masking" setting, similar to the "attribute masking" setting, that you can choose to turn on or off when setting up the game. If you set it to 'off', fitness will still be displayed in percentages as in previous versions, or alternatively, if you set it to 'on', fitness will be displayed in a range of coloured hearts. That way everyone is happy. Having hearts represent a range of fitness level (e.g. 90 - 100%) also might make the game more challenging to those who feel it's too easy at the moment and add more realism to those that feel percentages don't accurately reflect the way fitness is measured in real life.