Often it's just running around the park, chasing birds and squirrels through the grass/dirt etc... I can never catch them but it's a good playful sprinting challenge that I think activates more muscles and brain cells than just sprinting a straight line on pavement.
Sometimes it's exploring the great outdoors. I don't just hike the path like a lemming. I dart about like a child playfully analyzing the plants and bugs (just as a paleo man would) and checking out nooks and side paths. If I'm hiking near a small creek I find myself frequently jumping across it to check out both sides. Discovery is play.
I'm not too into sports but if you are, of course, playing them counts as good exercise and is probably a lot better for you than hitting the tread mill or running on the sidewalk.
Playfully wrestling with your significant other is great fun and also activates many rarely used muscles and brain parts and gets your heart rate up (more than just the physical exercise would).
Sometimes I go up the river/creek and start digging trenches or moving rocks to divert the water flow just for fun...
I could probably come up with 50 more examples. What's important is to get off your arse and have a little fun now and then. I think "fun" - especially the physical kind - is at least as important as your standard routine exercise regimine.
I have been playing alot more since I got a dog a couple months ago! I play with her in the yard every day. She loves chasing me around the house (and we both get a workout!). She is pretty attached and wont play outside unless I am with her so I even find myself just hanging outside in the yard, searching for 4 leaf clovers or looking at plants while she gets some excercise.
I am a grad student and find myself having a hard time taking study breaks and get outside. She has been great in forcing me to get out and relax and play again! Also, its worth noting that my blood pressure had been getting higher since starting grad school and is back to normal after a couple months of outdoor play!
Not nearly as much as I did when I was younger. My primary play habits are:
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