Fitness spring bar calorie burn help

Hello all. First time posting, so go easy.

I have a question as was wondering if anyone could help out. I own a fitness spring bar. different people call it different things, but its a large spring with a bar welded to each end, and red grippy handles to hold. (if you need a picture to help understand its here - http://fit4youfitness.com.au/shop/upper-body-fitness-power-twister-bar-double-spring-flx)

So i have this spring bar and have been doing 2 repetitions of a set of 5 every day. i can feel it in my biceps and i actually feel stronger than when i started, but i have no clue how to find out how many or even if any calories i'm burning. if i could figure out a calorie burn for a single rep, i could multiply that by how many repetitions a day i do.

Any help figuring this out would be excellent, and im willing to answer any questions to arrive at a burn count. thanks.