The following is a reply I got from Polar re same question:
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Thank you for your email.If you are familiar with the computers and know how to edit a file, here is instructions how to combine two exercise files:
1. Open the .hrm file that data you like to add to another .hrm file in Windows Notepad. Select "All Files (*.*)" in the "Files of type" field to see the .hrm files. 2. Copy the desired heart rate data from the [HRData] section in the end of the file. 3. Then open the .hrm file that you like to paste the extra data. Browse to the [HRData] section and paste the HR data from the Clipboard in the end of the list. 4. Sum the exercise durations of the combined exercises and change the value on the "Length" row in the [Params] section. 5. Save the new file. If you like to rename the file use the "Save As" function. 5. Open the combined file in the Polar Precision Performance SW 3.0 and edit the other data (lap times ect.) as desired.
Note! Backup the files before editing!
Unfortunately there is no parameter for the function you have requested, the only way to avoid this situation is how you have done it, i.e take the HRM with you, when pausing the exercise.
Best Regards,
Petri Tsokkinen
Technical Support Consultant
Polar Electro Oy
Finland