Definition of 'hard' is inifnitely subjective.

The body has its limitations and you can only put in what you got. You won't be able to convince me that Wiggins works any harder than Federer or Cavendish harder than Bolt.

Different sports develop different traits - someone said to me once that sprinters develop the ability to endure massive amounts of pain and endurance athletes develop the ability to suffer. Neither are particularly appealing to most.