logging TRX class

Hey everyone! Just wondering if anyone here does TRX and what do they log it as? Ive started TRX/kettle bell combo classes and its really frustrating not being to log it or having the faintest idea of what I burn calorie wise. I don't have a HRM yet so if someone could give me a rough idea that would be great :smile: Since I'm finally making an effort Id like to be log it :tongue:

Also I have a polar FT4, is it possible to get a chest strap seperately? I lost mine but will any polar chest strap do or does it have to be a certain model?

Thanks in Advance! :flowerforyou: