Has anyone found their Fitbit underestimates its cardio load recording? I don’t have any specific data (other than the HR I see on my Fitbit is very close to that seen on zwift using a polar heart strap).
However… yesterday for instance I did one hour of TR endurance… sweated buckets… 48 TSS. It felt like a good workout but Fitbit gave it a cardio load of 102 versus a daily target of 144 to 185. On that basis I will only ever hit my cardio target on days when I do very hard workouts.
1hr Endurance or 48 TSS shouldnt really feel like your sweating buckets (through effort, not room temperature).
Two thirds of your daily target being covered by such a workout sounds about right to me.
Unless you’ve set a custom max HR Fitbit is using 220-age, which is wrong.
It then uses that wrong estimate to calculate your zones bases on heart rate reserve. MaxHR-resting heart rate, at least the resting heart rate should be accurate.
From my experience I don’t think that the Fitbit algorithm is very good at estimating heart rate zones with people that have good metabolic fitness. Compared to power based fitness tests I’ve done the zones are 10-20bpm lower
I also find my Fitbit slow to respond to increases in HR and routinely under reports HR at anything over about 100bpm compared to my Wahoo Tickr chest strap.
How do I track heart rate with my Fitbit device? - Fitbit Help Center
… sweated buckets…
How much you sweat has no relation to how hard you were working.
cardio load of 102 versus a daily target of 144 to 185. On that basis I will only ever hit my cardio target on days when I do very hard workouts.
Or ride for another 30-60 minutes at endurance pace. 2hrs Z2 every day is sustainable, 1hr of Z3-4 is not.
Hi, i have just checked and I set the max HR based on a recent zwift crit race that I won (but nearly died in the process lol).
Re sweating … was just my flippant way of suggesting it wasn’t a walk in the park 
Was the max HR recorded on your fitbit or a proper chest strap?
1hr Endurance or 48TSS should be a walk in the park.
You should be getting off thinking I could have done that three times over
In my defence it was in ERG mode and all at the top of zone 2… so no freewheeling whatsoever for an hour is still tiring.
How do you get on when doing a 1hr Threshold or SST workout?
Wondering if your FTP maybe set to high
I’ve only done 2 workouts as very new to TR. Will see how it goes over the next couple of weeks. I do feel very fatigued which won’t be helping things.
FTP was set based on several years of Zwift, and more specifically a couple of recent crit races where I really went for it. But could still be wrong… I’ll do a ramp test soon
Z2 should feel boring not tiring
It often can, but as I said the top of zone 2 for an hour with no free wheeling is still tiring.