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Index S2 Body Fat% algorithm & age. Test

AlbertoGaMo
over 3 years ago

I have just tested Index S2 changing only my age. I have compared it with a Tanita and a Withings scales.

Me. 48 years Triathlete not pro. Right now off-season, finishing the recovery process after an injury.

Height 1.90m

Precompetition  BF%7-%9. 

Today weight Tanita RD545: 78.6kg BF% 11.9% BW% 63.5 Bone Mass: 3.4Kg

Withings Body Cardio+: 78.6kg BF:12.0% BW% 63.3

Index S2:

1st test: Age 48 (Real) 78.7Kg BF% 15.7 BW% 61.6 Bone Mass:4.9Kg

2nd test (2min later) Age 28  78.7 Kg BF% 13.5 BW% 63.2 Bone Mass 5.8Kg

3rd test (1 min later) Age 22   78.6 Kg BF% 12.6 BW% 63.8 Bone Mass 6Kg

4th test (1 min later) Age 20  78.6Kg BF% 12.6% BW% 63.8 Bone Mass 6.1 Kg

After the test, I seems clear the algorithm depends on Age and not only that the Body water and body Mass change too.

Please Garmin could you tell me how is this possible?

  • 0 over 3 years ago

    I have a theory about this: A sport age is also calculated in the VO2max evaluation. For athletic people this is probably around 16-20 years of age, which would then also be suitable for those for whom the index S2 is far off. It seems that the programmer is simply taking the real age and not the sports age calculated using VO2max. As a result, all results are always calculated as if one were hardly doing any sport (or as much as the average of the population), whereby the sport age corresponds to the real age.

  • 0 over 3 years ago

    Great theory, and it seems accurate with the results. My fitness age according to Garmin is right now 20 years old.

  • 0 over 3 years ago in reply to RoWe

    Dont agree. Why Tanita is making analysis well with less info about measured person? Garmin has a lot of additional long time informatin about other body condition (heart beat, training hours, etc.) therefore measuring should be more accurate. Understood, that BIA has limited accuracy and it isnt important for me if shows BF 19.0 or 20.0. But if shows 26 because Im 52, then its usable as BMI.

  • 0 over 3 years ago

    There is fact, if I change my age on Tanita's settings or Withings my BF% doesn't change as it should be. I've tested today 4 times my S2 changing only my age and the data has changed except the weight. If the only accurate value is the weight, then a 30€ scale should be enough and I'm sure that Garmin can make great products or at least accurate ones. That's the reason I bought one

  • 0 over 3 years ago in reply to AlbertoGaMo

    I am complete agree with you and that is exactly what I mean. You confirmed my previous experince, expensive device with limited accuracy, only one benefit is automatic data transfer. So, will wait few days if Garming will make some answer to your finding. But actually I'm thinking about returning the device.

  • 0 over 3 years ago in reply to 6734807

    I'm not evaluating Garmin's formula. I only mean that this could be the calculation error in index S2: The programmer was instructed to use the sports age to correct the BF, but instead used the real age. Of course, this indicates a formula based on BMI that includes VO2max.

  • 0 over 3 years ago in reply to RoWe

    Actualy, if any setting has an impact, it's not the VO2max age, but the activity class. Of course, also age and height are important as well as proper weighting "technique". Having said that. Even if everything is set and done properly, some still seem to see some off values. But it's always right to first check all the proper settings (activity class gets forgotten a lot) and how to properly weight yourself. Afterwards, it's a support/RMA case for Garmin.

  • 0 over 3 years ago

    My activity class is 10 as I usually train 18-20 hours per week. I haven't changed it anytime. Only the age and I cannot understand why the real age has to impact in BF% and not the internal sensors of the scale.

    It would be great if someone from Garmin could tell us a bit more about these inconsistent values.

  • 0 over 3 years ago in reply to RoWe

    Have you seen it yet? Garmin Connect now shows the fitness age in a new overview. Unfortunately, the formula has probably also changed. It now calculates the body fat that the index provides. Well, we won't get out of the deadlock anytime soon.

  • 0 over 3 years ago in reply to AlbertoGaMo

    activity class is the setting that garmin use to adjust for fit people. unfortunately even on the max it does not reflect reality for even amateurs let alone pro athletes

    age should not be relevant. it is true that BF tends to increase with age, however this is not a rule, just common practice as people get lazy. the purpose of body composition scales is to help us ensure that our BF does not increase over time, not to echo back at us the expected trend that it will.

    garmin could indeed use their own derived fitness age which would be better than activity class since it is based on real data rather than an individual's own perception. this would be a very good solution, shame they have not done so or made use of any of the other information they have about a user.