Garmin Vivosmart HR (9) ~ Wrap up

 Vivosmart HR

Wrapping up Vivosmart HR

   I have been using Garmin Vivosmart HR about a half month.  Overall, this is a good one to keep tracking daily activity including heart rate 24/7.   The embedded wrist based heart rate sensor gives very similar reading as a chest strap heart rate sensor I have been using for a while.  The detail review is still on-going, however, overall it is reasonable to monitor the heart rate based on the past data I got with my usage, such as running, walking, hiking and cardio in a gym.  I probably keep using the chest strap sensor for running.  But it is probably good enough for hiking based on the result last 2 weeks.  Here is summary what I feel about this product. 

Battery life

   With my current usage, which is wearing the device almost all day with 30 minutes to 90 minutes workout with heart rate monitoring, the battery life with a single full charging is about 3 ~ 4 days.  So I probably need to charge the device twice a week.   I have not tried to use this device with activity tracking mode for very long time like all day yet.  However just check the heart rate, we do not have to use activity tracking mode.  Therefore, we will be able to use at least 3 ~ 4 days without charging again.  The heart rate sampling in non-activity tracking mode would not be so often.  However it is probably all right for managing the pace during a hiking I have been talked in this blog.

Sleep tracking

   This feature exists in the previous model “Vivosmart”, however, the auto-sleep detection feature is much better in Vivosmart HR.  For most of automated detection, I do not have to adjust it.  This is a big improvement from the previous model.

Display

   It is also improved from the previous model.  It is better even if under sun light.  Also, I think the operation is improved as well.  In the previous model, to enable the display, I need to tap the display.  Also to get a menu, I also need to hold the display.  In the new model, the basic display is always on and there is a dedicated button to get the menu.    The touch screen operation is also getting much better.  In my opinion, it is much better to use this device than the previous “Vivosmart” during hiking.  Although the heart rate trend graph is small, it is a good information to see the heart rate trend during hiking.

Activity tracking

   The menu is changed, there are categories, running, walking, cardio and others.  I do not know what is actually different between them.  At least running and walking, they are using different a step length to calculate the distance.  Also, there is no distance / pace information for cardio, only heart rate information shows up in the result.

   The big difference from the previous model is Vivosmart HR has embedded wrist based heart rate sensor.  Therefore, I do not have to wear the chest band based heart rate sensor to monitor during a training.  The detail evaluation is still on-going, but so far I am getting very good result for my usage, such as running, walking and hiking.   As I mention earlier, I would probably use the chest strap sensor for some training for running, but it is good enough for hiking and some “casual training”.   Especially some indoor activity which cannot be tracked with GPS, this is a good device for such purpose.

Floor climbing

   In the Garmin web site, a feature table shows there is “barometric altimeter”, however, it is not really “altimeter”.  The feature probably just using to find out “stair climbing”.   It shows some, however, it is not very useful for me.   So I disable this display.

24/7 Heart Rate Monitor

   This is a new feature.  For most of healthy people, they might not be interested in so much.  However, I am interested in this feature to see if there is any difference between the daily heart rate and high altitude environment, especially during sleep.  Actually, that is one of motivation I am evaluating the embedded wrist based heart rate sensor.  This would be an interesting data after the actual walking to see if there is any new finding and some sign for the altitude acclimatization.  Overall, the embedded heart rate sensor could be close enough to check this type of data.  So I will plan to capture some data in my next Mt. Whitney trip.

  Also, it is very easy to figure out the resting heart rate for the heart rate zone definition.  There are a few different method to define the heart rate zone for the heart rate based training.  One is using just the maximum heart rate with a percentage of the maximum heart rate.  The other is using reserved range which is defined by the resting heart rate and the maximum heart rate.  The second option would be a better way to define the heart rate zone in my opinion.  The Garmin device has another setup based on a lactate threshold.  However it is not easy to find out a person’s lactate threshold.  There are some devices which can estimate the lactate threshold value.  That would be another item I want to evaluate in the future with the other device. 

Wrist based heart rate sensor

   To measure heart rate during a workout, I used to use chest strap heart rate sensor during a workout.  I compare the measurement data between the two sensors how much gap we can see.  Based on my experiment, overall reading is close enough for typical running, walking, hiking and cardio in a gym.  The both sensors might have incorrect reading sometime.  I am not really sure why the incorrect reading happens.  I usually wear them almost the same way and the incorrect part is not the entire workout, it is usually just a part of workout only.  Once one of sensor reading becomes incorrect the offset between the sensors is getting bigger.  Based on the past data, the chest strap type sensor tends to be inaccurate in the beginning.  However, I saw sometime in the middle of a workout.  The wrist based sensor sometimes gets incorrect reading anytime or random, but usually the duration of incorrect reading is short, most of them are spike.   Overall, the chest based sensor gives us more stable reading comparing with the wrist based sensor.  It seems the chest strap sensor could be more accurate than the wrist based sensor in general and I probably continue to use the chest strap sensor for some point training for running.  But for a casual running, jogging, walking and hiking, I would use the wrist based sensor.  It is much easier for me not to wear the chest strap sensor for those activities.  Especially during hiking, without wearing the chest strap based sensor, I guess I would be much more comfortable in many cases.

   One item I have not done my testing is broadcasting the heart rate reading through ANT+.  Basically for the other device such as handy GPS device with map, a legacy GPS watch which requires an external heart rate sensors like my Forerunner 910, they can pair this Vivosmart HR and we can get the heart rate number instead of the chest strap sensor.  This feature is probably useful if people using a handy GPS device with map to log a hiking data.  This is one of good option to track heart rate and the location information during hiking.  I will plan to do some testing in the future. 

My conclusion

   Vivosmart HR is a good device to track daily activities.  It could be a good option to use for the heart rate based pacing I have been talking in my posting.  This device can broadcast the heart rate data to the other device through ANT+.  Therefore, we can track the locations and heart rate with those device.  It is a good option for hiking.  The battery life with some active tracking mode is something around 3~ 4 days.  So most of hiking can be covered.  The handy GPS device is usually using standard size of battery and it is easy to replace.  Thus, people do not have to worry about the battery life so much.   The high end running GPS device with longer battery life is usually very expensive just for hiking.  Unless people also do some serious running, it might be too much.  I am basically stick to Garmin due to the past data in Garmin Connect website, based on the recent product line, running GPS devices battery life is something around 12 hours for most of product.  They are probably not enough for most of people for a day trip to Mt. Whitney.  The round trip probably takes more than 12 hours for most of people.  So for those people, they probably need Forerunner 735 / Fenix 3 with the embedded wrist based heart rate monitor to cover a day trip hiking to Mt. Whitney.  People just need up to 10 hours a day, then they have more choice to pick low end models which is starting from around USD $200, such as Forerunner 35, 235, Vivoacitve HR and etc.  If people look for a low cost solution, Vivosmart HR could be a good option

Garmin Vivosmart HR (8) ~ Statistics for the offset

Statistics for offset between the chest based sensor and the wrist based sensor

Statistics for the offset

   Today, I show a statistics for the offset between the chest based heart rate sensor and the wrist based heart rate sensor.  This is based on the past half month data.  Since the number of samples for each data is different, using the percentage of the total samples for each data to compare them.   As you can see, more than 90
% samples are within less than 4.

   Then, I can look into the worst a few data.  The worst one is a data on September 14.

The worst data on September 14

  The orange is a data for Forerunner 910XT with the chest based heart rate sensor.  In the middle section, the chest bases sensor reading shows much higher value.   However, those reading is probably incorrect reading.   The heart rate should not be around 180 bpm in that section.  So I would assume the data read by Vivosmart HR could be close to the real value.   This means, the offset is due to wrong reading by Forerunner 910XT in this case.

   The second worst data is September 23.

The second worst data on September 23

   The blue is a data for Vivosmart HR with the wrist based heart rate sensor.  In the beginning, there are a several spikes on the reading by the Vivosmart HR.    For this data, I do not believe the reading value by Vivosmart is correct reading and the offset is due to this wrong reading.

The both sensors might have incorrect reading

   This data shows the both sensors have a chance to get incorrect reading.   However, I have no idea why it happens and where it happens.   For the both examples, they show a part of period gets larger offset and the other parts are matched well.   The offset is not due to a problem of the wrist based sensor.   As long as the both sensors read reasonable value, the trend would be close enough.   I am not sure if this offset due to how I wear the sensors or not.  But the bottom line is the both sensors might have incorrect reading.  So as long as, people recognize this, it should not be a big problem for general usage.  The data shows majority of samples are reasonably close each other.
   Please note, this data is collected for running / walking and cardio exercise.   For those type case, the wrist based sensor could be all right to use.   Actually, it is a benefit not wear the chest based sensor.

   I will continue to collect the both heart rate reading data during my training for a while.  To see this result is consistent or not.   Overall, the incorrect reading happens in different type of exercise.  It also happens in random.

Garmin Vivosmart HR (7) ~ Quantify the offset Part 2

Data on September 20, 2016

An example with a similar trend

   In the previous post, I showed a data with big offsets during some period.  This post shows a good data which has smaller offset.  The plot above shows the trend is almost the same between the chest band based heart rate sensor and the embedded wrist based heart rate sensor.  I applied the same method to calculate the offset and plot.  The following is the plot for the offset distribution.

 The offset distribution

   This plot shows majority of samples are in a group that the offset is within 2.   It is hard to tell if there is any difference on the first plat.   However, there is a portion the offset is bigger in the beginning where the heart rate value has a big transition.  The reason is not very clear with the data I have.  But it may be the following reasons:

• In many cases, the reading in the beginning of the training is not very accurate
• It is probably the offset is bigger when it has a big transition

   We might need more data to tell the clear reason.  I plan to correct more data and analyze them.
   It is clear that even if the heart rate trend looks a similar, but there are some big offsets.   It is hard to tell where the offset is coming from.   I guess it is worse to analyze the data more.

Actual amount of offset?

   Now, to check how much offset we need to consider to use data, here is another plot that indicates the amount of offset and total number of samples for each offset group.

 Distribution of samples for each offset amount

   The data shows more than 92% samples are less than 2 offset.  The other observation is that a section which has a big offset is only beginning, the rest of parts are really stable and matched.  Based on those indications, it is worth to evaluate to analyze the offsets to quantify the offset.
    Based on the data I posted last week, it seems that data for outdoor running has some bigger offset than the indoor training in a gym, such as elliptical, stair master and so on.

Other finding

   When I analyzed the data, I found out the sampling is not synchronized between the two devices.  Especially the data sampling rate between the two devices is not the same.   Even the same device in the different training log has some variation.  The overall sampling rate is something around 3 ~ 7 seconds.  But I have no idea how a device defines the rate.
   As an example, Vivosmart HR data on September 21 has every 4.1 seconds as an average, the minimum is 1 second and the maximum is  25 seconds.  On the other hand, Forerunner 910XT has every evey 4.2 seconds as an average, the minimum is 1 second, and the maximum is 10 seconds.  The entire training data is for 1 hour.  The total number of sampls for Vivosmart HR is 910 and 898 for Forerunner 910XT.

  In addition, the heart rate data for Vivosmart HR is 143 [bpm]  per minutes as an average, 76 [bpm] for minimum and 169 [bpm] for the maximum.  Forerunner 910XT, it shows the average heart rate is 146 [bpm] , the minimum is 80 [bpm] and the maximum is 168 [bpm].  I think they are close enough

Garmin Vivosmart HR (6) ~ Quantify the offset between the two heart rate sensors

 Offset distribution

Quantify the difference

 

　　　First of all, this review is not verify the accuracy of the sensor reading.  The primary purpose is to find out how much difference between the two sensors, especially if we can replace the chest based sensor to the wrist based sensor.  Last week, I showed the sensor reading plots on the same scale.   Overall, it seems to be close enough in most of cases for running / hiking / cardio in a gym.  However it is not enough to show how much closer.  Therefore, I have been working on quantify the difference.

A method to quantify

　　　One of ideas to show the difference is to check the offset distribution.  The distribution could show what the offset looks like.  The problem to get the distribution is the both devices are not synchronized for the sampling.  So that I wrote a program to fill a value if data for one of device is missed.  The program find out the last valid sample data and the next sample data.  The assuming value between the two samples are linear.  Then, calculate the offset between the two devices and find out the distribution based on the offset amount.

　　　As an example, I used a training data for today.  I did a “threshold run”.  

• 10 minutes warming up
• Run in Heart Rate zone 4 for 4 minutes, run in Heart Rate zone 2 in 20 seconds – Repeat 3 times
• Cooling down 10 minutes

　　This is a part of Garmin full marathon training plan.  This menu is “Week3/Day4”.  This is a sort of an interval training.

Here is the offset distribution:

Offset	Number of samples	[%]
0 ~ 2	668	58.3
2 ~ 4	100	8.7
4 ~ 6	35	3.1
6 ~ 8	25	2.2
8 ~10	24	2.1
10 ~ 12	23	2.0
12 ~ 14	24	2.1
14 ~ 16	24	2.1
16 ~ 18	14	1.2
18 ~ 20	21	1.8
22 ~	212	18.5

This example shows the reading does not match well.  Here is the plot.

 Heart Rate plat for Threshold Run on September 21, 2016

Also, this is the offset looks like.

 The offset distribution with Time

　　Based on the plot, it seems that Forerunner 910XT reading which uses the chest based heart rate sensor does not get correct data in the beginning. After that section, the both reading is getting closer.  However, there are a few spikes on reading by the Vivosmart HR.  They are probably not correct readings.  As long as people are aware of this behavior, they are not a big deal in my opinion.  I also did a similar training last week and the data showed a similar result.

    I will apply this scheme to other data to analyze more detail.

(To be continue)