Heart rate at each of BREAK_OFFSETS seconds into the break, null where the break had ended or there was no reading.
How long it lasted, seconds.
Heart rate over the 15 seconds before the slowdown.
Seconds from the activity's start when the slowdown began (found from speed over 10 s, so a sudden stop shows a few seconds early).
Heart rate at each of BREAK_OFFSETS seconds into the break, null where the break had ended or there was no reading.