Heart rate monitor for scientific study
I recently completed a study involving physical ergonomics of rifles.  We monitored heart rate and respiration using the Zephyr BioHarness.  It seemed to work pretty well.

It also monitors movement of the user, if that is of interest to you.

To get data out, it is possible to compile a report and export it to CSV, which works well if you need to do analysis on the data using other programs.