a spark in the snow

These kick sleds are lots of fun. If you are a grown-up it's not so easy to just go out sledding, but if you have a spark (it means "kick"), you can sled standing up and look like you are just going about your normal business. Nobody needs to know that you're actually just having fun!
They are great for the old folks who need walkers, instead of wheels on the walker there are runners. If they are feeling frisky they can put one foot on the foot pad of the runner, hold on to the handlebars and kick of as if they where on a skateboard! (skateboard with a handle that is - what are they called? I remember at the train station in Vienna I saw a young gentleman in a suit gliding along the platform on his skateboard with a handle, we got to the train and collapsed his pogo stick(?) no, what do you call it?? and jumped into the train!)
Anyway this is about the spark, they are lots of fun unless the road has been sprinkled with salt or sand.

In this picture my uncle is just learning how to operate the spark and in the next one he's winning the town championship in kick sledding. It was one sport he could compete in without noticing the handicaps he was left with from polio.