Record and Analyze HRV from 910XT
Enable RR recording
Turn on the FR910XT and go into the menu screen. Press UP then DOWN and repeat 10 times (if you count up-down as one cycle then this is 5 cycles).You should now have entered the "diagnostic menu". From here select HRV on the top and press Enter. Now you can enable the hrv recording.
Getting RR values from FIT
For now I used fitdump and awk/sed to get rr values from the fit file into another file.fitdump activity.fit |grep -A1 hrv | grep time|awk '{print $4}'|sed 's/(\([0-9]*\)),/\1/g'
If there's values much too high you could filter them e.g.
awk '$1<1500'
Analyze
You can use the hrv toolkit.
plt_rrs -m -R hrv_values1
get_hrv -m -S -R 2012-06-24_08-08-32-80-97354.hrv
Or there is the HRV Analysis which is a windows application but works under wine:
Or for some less sophisticated plot try this, use the above output and filter again with awk:
awk ' { OFS="\t"}{total=total+$1; print total,$1}' > hrv_values
gnuplot:
gnuplot> plot "hrv_values" using 1:2 title 'HRV' with impulse
gnuplot>