It has to do with margins for error.
Normal heart rate is between 50 and 100 beats per minute. If you measure for less than 20 seconds, the result may be unreliable because to calculate beats per minute, you will need to multiply the result by a number depending on the lenght of measurement. Say you count five heart beats in five seconds. You multiply by 12 and get 60 beats for every minute. However, if your measurement is off by one half second either way, when multiplied by 12, it will amount to three seconds of error. If you measure five heart beats and the sixth comes right after the time ticks over, that will also lead to error.
When measuring for more than 20 seconds, you increase the chance for miscalculation by missing a heartbeat or counting it twice, your heart rythm may change or you may miscalculate time or make an error in converting to beats per minute as everything between 20 seconds and one minute exept for 30 seconds will mean decimal calculations. With a stopwatch, however, you can measure for full sixty seconds and get a reliable result.
When you measure your heart rate for less than 20 seconds , why is it less possible for the results to be reliable?
When you measure your heart rate for more than 20 seconds, why is it still less possible for the results to be reliable?
1 answer
1 answer