I do a couple of primitive biathlons each year, Jeffersonville and Manchester VT.
There are "gazelles" who run it and the rest of us who stride purposefully. Sometimes I do it timed and sometimes I just walk along with an older friend of mine and enjoy the conversation.
Both places have attractive hardwood forests to walk through, friendly folks, and the challenge of shooting when you are breathing hard. The Manchester shoot also has some stationary target events.
The weather in Jeffersonville can be challenging - I've done it at -4F with a stiff breeze. Most of the time, though, it's in the 20s or better and I find myself sweating a bit after a quarter mile on snowshoes. The key is to start a little slower than you want to and then accelerate as you warm up. Easier on your lungs with cold air. Then slow down a little just as you come into the target area to let your heart rate and breathing slow down.
I'm always competing against my own score from last year. I've competed with both flintlock and matchlock with moderate success. It's more fun than the proverbial cylinder of simians. Do it!