i've heard its bad to spar and use the sauna afterwards, i looked around on the net but couldn't find anything. does anybody have any insight on the dangers it could present?
It's not bad per say, more after a sparring session you may be slightly dehydrated. Jumping into the sauna and losing even more water weight may result in you passing out, getting light headed and slipping etc etc.
Use the sauna to recover in after a hard day's training, on the night, on your day off or on the weekend. Sauna's are simply amazing. Love them so much!
I use the sauna all the time after training/sparring. My buddies don't always like to so it is really just personal preference.