Wednesday, October 2, 2013
Exercise Estimates - Trying to be Truthful
As I exercise, I get quite a bit of feedback. My machines give me an estimate, my Fitbit has a calculation, my heart rate monitor comes up with another number. At times, I'll even check an internet calculator for an online opinion. Occasionally (but rarely) these numbers are similar, and then I feel fairly confident that the calorie burn is close to correct. But other times ... HUGE variations between the different devices. I've been getting a lot on inconsistent readings from my bike workouts especially.
First, Fitbit (I LOVE LOVE LOVE my Fitbit, check out my post Wondering about a Fitbit ). Now, the Fitbit should be worn on the torso or waist (wrist only for sleeping, or if you have a Flex). Wearing it on my sock, while biking is NOT how it was intended to be used for an accurate calorie or distance/step count. I was really only looking at Fitbit's numbers out of curiosity, but it's a good thing I didn't default and assume it was correct ...
So you can see, I have two activities recorded this day. The first was a 1.5 mile jog. The second was a 10 mile stint on the stationary bike. Although the bike ride took almost twice as long (37 minutes opposed to 18 minutes), the step count is similar. So I have no idea why Fitbit estimated the bike ride SO high at 350 (it's often been almost up to 400). It is certainly no where near the same intensity as jogging (I keep my stationary cycling pretty leisurely, reading while I ride). So I always go in and adjust the calorie count down ... but down to what?
The bike itself estimates a calorie count between 230-250 for my 10 miles. The bike does ask for my weight, it knows the actual distance and the difficulty level ... so it should be right, right? Well ... not according to my HRM!
My Polar takes into account all my stats (weight, age, sex ... as does the Fitbit). Of course it also uses heart rate to calculate an exercise estimate. Generally, HRM are considered accurate for "steady state cardio" ... but less accurate for other activities. You can see my Polar comes in quite a bit lower (157 calories) than the bike readout. During my ride, I never got my heart rate up "in the zone" ... even at a pretty steady 16mph, it doesn't feel like I'm working that hard. I'm really using the time for reading, just doing it on the exercise bike so I feel less guilty about spending so much time with my books (Riding and Reading). If I can do both at once, whatever the correct calorie count ... at least it is something!
So as I gather all my estimates ... I most often take the lowest one. That is usually the HRM. The machine readout is generally highest, with the Fitbit somewhere in the middle. For a straight walk/jog on the track, the Fitbit and HRM are usually almost identical. For DVD workouts (cardio or 30DS) the HRM is generally higher than Fitbit.
When I'm entering an exercise manually into Fitbit, Fitbit also subtracts a little bit to take BMR into consideration (what I would have burned during that time anyway, as Fitbit takes that into it's total estimate for the day). I really TRY to be truthful with my exercise estimates. I know it does me no good to overestimate the numbers ... my body will burn what it burns no matter which estimate I write down.
Do you feel you are getting accurate calorie burn estimates?
Which devices do you trust most?
How important is an accurate exercise calorie count to you?
It isn't just the calorie count that has me confused ... my "step" count for my bike workouts come in vastly different some days. Generally, my Fitbit and Omron pedometer are fairly close at the end of the day. As I'm averaging 22,000+ a day, variations of a few hundred don't seem bad. But I noticed on some cycling days, I was getting some big differences (2000+).
Here's a snapshot of a before/after ...
Now I must say upfront here ... pedometers are NOT really meant to track cycling. I know this. For my own personal records though, I like to get step "credit" for the times I'm on the bike. I move my pedometers to my sock (NOT how they are intended to be worn) and get some "step" credit close to what I would have received if I'd spent the same amount of time on the treadmill or elliptical. But you can see (above) ... the two devices can count "steps/revolutions" VERY differently. It's not always the case though, here's another workout ...
... on this day, the counts stayed almost exactly the same!
I'm not sure if I'm placing them differently or what.