One thing emphasised by both the paleo philosophy and simply by virtue of watching my kids entertain themselves, is the notion of play.
It can be initially difficult to reconcile the idea of play leading to a subsequent improvement in fitness. Even when we play games such as football (soccer) or racket sports, it is easy to get seduced in to the 'harder and more of it' mentality, where the fun is edged out by competitive instincts, leaving us with the notion that we will only get better if we take things 'more seriously'.
But play CAN lead to improvement. We know that power law training will elicit the desired improvements in, for example, strength, but this is only one side of the coin; play does something much more than that. It should lower mental stress and anxiety, NOT pile it on. It should induce a general sense of wellbeing. Play should lead to inner growth and 'release'.
I mention this because if you follow this link, you will see five minutes of footage that absolutely, bang on the money, nails EVERYTHING you could want to know about the benefits of play.
I am sure Danny MacAskill takes his riding seriously, but how he expresses himself on a bike shows passion, ingenuity, novelty, adventure, excitement along with strength and, acrobatic and athletic ability. This is one of the best examples of REAL play in action! The guy is having fun!