Why is she running?

I went for a run yesterday and a four year old child in a pushchair said as I passed, "Mummy, why is that lady running?"

I wanted to say, "because I love to run!" but I didn't, because it felt slightly mental and also I wasn't loving running much at that moment!
I was more curious to see what her mother might say in response.  It's so interesting that a young kid would view running as a strange and rare occurence for a grown up to be doing. Her mum was a little embarassed and said quietly "She's just running. Um, er,  you run sometimes don't you!"

Imagine the world in a future where the need to run decreases to such an extent, and maybe even walking becomes rare, or moving at all becomes unnecessary.... How little will people need to move to survive?
 We can already order groceries and almost everything we could possible need direct to our homes. There is a new phone app which enables us to have a lover at our front door within minutes- so no running involved in that game anymore!