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Data Accuracy - Garmin 235 vs 305 (with thread text)

Former Member
Former Member over 9 years ago
Hello all, I recently purchased the forerunner 235 to replace my old tried and true 305 once it took 10 plus minutes to acquire satellites prior to a run. Overall I would say that I'm happy with my 235. It has more bells and whistles than anything I was expecting. I don't like wearing chest strap HMRs so the OHRM was one of the main reasons for buying it over 230. I am however unsure of the accuracy of the OHRM (based off of what I have read here) and how that in turn affects the calories burned in the data summary. I would like to say that I know the calorie count is an estimate at best so "calorie trolls" please move along. What concerns me is the variance in the number between the two devices and how I would be more inclined to believe that my 6 year old device is giving me a more accurate assessment. In reality I would like to get as close to the ground truth as possible. Additionally, I would like to say that the smart features and GPS tracking has been spot on. OHRM and statistical accuracy while running is far more important than sleep data. I could really care less about how much a twitch and move at night.


Here is an example of an almost identical run and pace. Calories burned 571 vs. 283

305:
4.23 mi Distance, 7:48 min/mi Avg Pace, 571 C Calories, 32:59 Time 102 ft Elev Gain
https://connect.garmin.com/modern/activity/1006060441

235:
4.27 mi Distance, 7:34 min/mi Avg Pace, 283 C Calories, 32:16 Time, 130 ft Elev Gain

https://connect.garmin.com/modern/activity/1124262938

SO what do you think? Is the difference in stats a OHRM issue or a software issue?

Note: All my stats are inputted and are identical in both devices minus HR which is 44 RHR and 185 Max
  • 0 over 9 years ago
    Firstly you need to make sure that things like Max HR and your other user profile settings are realistic for you. Is your max HR really 185? You only averaged 109 here. In other words, if correct, this was presumably a very very easy run for you.

    Secondly the calorie algorithm on the 235 takes a little while to "learn" you. Maybe 1-2 weeks depending on how often you run.

    Thirdly, I believe the 305 uses more of a generic algorithm. Even more so as you had no HR data with the 305.
  • 0 over 9 years ago
    109 bpm at an avg 4:42 min/km is very good!

    ....if you've ever used a HR monitor with the 305 how does it compare to the 235?

    Is it possible that the 235 was not reading your HR correctly, I noticed the HR graph is showing drop outs but you did not actually stop running during these drop outs..
  • Former Member
    0 Former Member over 9 years ago
    Firstly you need to make sure that things like Max HR and your other user profile settings are realistic for you. Is your max HR really 185? You only averaged 109 here. In other words, if correct, this was presumably a very very easy run for you.

    Secondly the calorie algorithm on the 235 takes a little while to "learn" you. Maybe 1-2 weeks depending on how often you run.

    Thirdly, I believe the 305 uses more of a generic algorithm. Even more so as you had no HR data with the 305.

    Here are a couple other runs as a reference.

    <iframe src='connect.garmin.com/.../1119058132' width='465' height='500' frameborder='0'></iframe>
    <iframe src='connect.garmin.com/.../1126691815' width='465' height='500' frameborder='0'></iframe>

    My max HR is based off of my RHR from my watch. I've used the watch for roughly two weeks now with about 10 logged bike and running activities. I believe the 109 HR was low and the 7 mile run HR is a more accurate assessment.
  • Former Member
    0 Former Member over 9 years ago
    Firstly you need to make sure that things like Max HR and your other user profile settings are realistic for you. Is your max HR really 185? You only averaged 109 here. In other words, if correct, this was presumably a very very easy run for you.

    Secondly the calorie algorithm on the 235 takes a little while to "learn" you. Maybe 1-2 weeks depending on how often you run.

    Thirdly, I believe the 305 uses more of a generic algorithm. Even more so as you had no HR data with the 305.


    Here are some additional runs as a reference.

    <iframe src='connect.garmin.com/.../1126691815' width='465' height='500' frameborder='0'></iframe>

    <iframe src='connect.garmin.com/.../1119058132' width='465' height='500' frameborder='0'></iframe>

    My max HR is based off of my RHR given to me by my watch. I believe the 109 HR was low and the 7 mile run will reflect a more accurate HR for a run.

    I've had the 235 for about 2 weeks now and have logged about 10 activities mixed between running and cycling.
  • 0 over 9 years ago
    RHR = resting heart rate so not sure how you can infer a max HR from that?
    Not clear to me yet that 185 is correct.

    How hard are you trying in that 2 mile track run? Average HR there is only in 130s. Either your 235 is reading low for HR for some reason or that was just an easy run?

    Ignoring the spike in the 7 mile run, your HR is in the 140s mainly so again a long way short of 185.

    Anyway, as for calories, I often take as a benchmark of about 100 calories per mile and those two runs aren't far off that.
  • 0 over 9 years ago
    Correct - resting HR has almost, if not zero relationship to maximum HR.

    I also reference the standard benchmark of 100cal per mile (which is high for small women and a bit low for large men) - only difference is when there is a lot of elevation involved or significant times spent in zone5 (due to after burn). Doesn't matter much how fast you go - still pretty close to that.
  • 0 over 9 years ago
    Hard to say without any comparison material but I'd say the ~110bpm avg at a pace of 4:42min/km is off (or you're extremely fit) and as a result calory calculation is as well.

    But again, hard to tell as the FR305 race isn't showing hr info

    *Edit* I know see the other runs as well, and the 7mile one (with a more realistic HR) gives a calorie estimation more in the range of the FR305 run
  • Former Member
    0 Former Member over 9 years ago
    RHR = resting heart rate so not sure how you can infer a max HR from that?
    Not clear to me yet that 185 is correct.

    How hard are you trying in that 2 mile track run? Average HR there is only in 130s. Either your 235 is reading low for HR for some reason or that was just an easy run?

    Ignoring the spike in the 7 mile run, your HR is in the 140s mainly so again a long way short of 185.

    Anyway, as for calories, I often take as a benchmark of about 100 calories per mile and those two runs aren't far off that.

    I was pushing myself during the 2mile run. I'm 34, 5'9, 177lbs for a frame a reference. According to calculations, my max HR should be 186. I'd also say I'm above average for overall fitness. I run and cycle roughly 3-4 times a week.
  • 0 over 9 years ago
    I'm 34, 5'9, 177lbs for a frame a reference. According to calculations, my max HR should be 186.
    Ah. Ye olde MaxHR=(220-Age) formula as an estimate of the ‘average’ that is accurate for a dubious proportion of the population. That doesn't tell you what your MaxHR should be; there is no such thing. Especially when,
    I'd also say I'm above average for overall fitness.


    RHR = resting heart rate so not sure how you can infer a max HR from that?
    I'm guessing he's mistaken, and he meant %HRR is calculated using the RHR as the lower boundary of the range, which is a user-selectable option on the FR235.