Chest strap base heart rate sensor
I have been
collecting data to compare the reading offset between Garmin Forerunner 910XT
with a chest strap based heart rate sensor and Garmin vivosmart HR with
built-in wrist based optical heart rate sensor.
As I posted before, the overall trend is close enough for my usage such
as casual running, walking and hiking.
Roughly more than 90% samples are within 4~6 offset.
Chest strap sensor
As I mentioned in
the previous post, I sometimes see inaccurate reading by the chest strap
sensor. In many cases, it shows
beginning of a workout. I also saw a few
cases out of twenty workouts after middle of workout. I think they are probably depends on how I
wear the sensor. Especially the offset
in the beginning is probably the sensor might not have a good electrical contact,
which might be higher electrical resistance between the sensor and the body. Once I started sweating, the contact is
probably getting better and getting a reasonable reading. When I saw the offset not in the beginning, I
think the sensor could be move / shift during the workout. I think the chest based sensor is probably
good as long as it has good contact to the body in my opinion. For more accurate measurement, it is probably
better to put some moisture when a person wears the sensor.
Wrist based sensor
First of all, to
get a good reading, it seems that we need to wear the device tight enough. If it is loose, it seems the reading won’t be
stable. This is a similar as the chest
based sensor. The device needs to have a
good contact. Once people understand how
tight we need to get the reasonable reading, the result is probably getting
better.
Based on the past
data, I do see two type of inaccurate reading.
One is some higher reading where the heart rate value has a peak. The maximum heart rate tend to show as higher
value than actual. As long as the
reading value is stable and the delta between samples is small, the reading
value against the chest sensor is almost matched.
The other
observation is it has some time has a sharp spike. I do not know why this happens. But I sometimes see. The duration is very small and overall heart
rete value is stable and no big transition overall. Just that short period, I do see very high
spike.
Because of those
inaccurate reading some time, the maximum heart rate shows higher than the
chest based sensor. I think that is one
of reason, Gamin does not offer to estimate VOmax / Lactic threshold by the
wrist based sensor.
Conclusion
Based on the date I
collected, the wrist based sensor is totally acceptable for my usage. People just needs to understand the behavior
that it shows a bit higher value sometimes comparing with the chest based
sensor. The both sensor might have error
reading, but the chest based sensor reading is much more predictable. The error reading on the wrist based sensor
could be more random and hard to predict in general. So if the heart rate reading changing a lot,
the chance of offsetting could be higher.
As long as the heart rate is stable, it is relatively close to the chest
based sensor reading and it is easy to tell if it has some inaccurate reading.
My opinion, just
using the reading value for pacing, the wrist based sensor is all right. If a workout make higher transition like
interval training, it is still useful to use the wrist based sensor, but the
chest based sensor can be much stable.
So, I probably continue to use the chest based heart rate sensor for
running especially interval and high intensity running. But I will use the wrist based sensor for
hiking and casual running.
This conclusion is
a similar as I concluded in the wrap up for vivosmart HR review. But with some extra data, I might have a
better explanation for the offsetting.
So far, the wrist
based sensor is probably a good option for many people.
Side note:
The battery life
for the broadcast mode is probably around 20 hours. So it is long enough for tracking the heart
rate with broadcast mode to the other device during hiking.
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