Treadmill read data

Hey guys,

I have some treadmills at they gym and some of them have a RJ45 connector. Is it possible to connect to the treadmill and READONLY the data like heart rate/speed/distance and so on? Any hints in starting this side project?
I believe that it might send some serial data through there, but I'm not sure.

Moreover do all treadmills have such a connector?

I'm sure all do not. Whatever is on that connector will be proprietory to that brand or even model.

Doesn't anyone at the gym know or have a reference manual for it.?
Most domestic T.M.'s don't have it.
Max.