Calibration of exercise machines

Lately, my various analysis of weight loss data plus adding the BodyMedia monitor and ActivityManager has slowed a slowdown in the weekly loss. I had drastically escalated my exercise (from a good base) but January will definitely be below the December rate so I’ve slowed down. Mainly this is accounted by the increased use of the new machine, the stationary recumbent bike.

All three machines (treadmill, bike, elliptical) report calories burned. Once I added the BodyMedia system (where I can get minute-by-minute profiles) I quickly learned the BodyMedia is really a glorified pedometer (measuring how intense steps are is its enhancement) so the smooth motions of elliptical or bike (which I want, long-term for my aging joints) are not counted as much.

So are the calories burned, as reported by the machines accurate? How can I compare the workouts?

There is the concept of “perceived level of effort” (basically how hard you’re huffing-and-puffing and sweating) and I already ranked my machines: 1) elliptical, 2) treadmill, and, 3) bicycle, but that didn’t give me any calibration factors (how to scale the calories reported by each machine so they are comparable).

Fortunately it turned out another piece of gear was lying around the house (unbeknownst to me) and that is a Polar heart-rate monitoring belt with wrist-watch display system. A-ha, now potentially I have something to use to compare.

And given all three machines have their own heart rate monitors (although different sensor technology) and I’d already seen wildly inconsistent readings I previously had not be able to use heart-rate as the measure of workout difficulty and thus as the basis for the scaling factor I’d need.

So after some fumbling around trying to the the heart-rate monitor working I finally completed workouts, at varying degrees of intensity, on all three machines. My subjective sense of which workouts are the most intense turned out to be correct. BUT, what was surprising was how low my heart-rate readings actually were.

I had trusted the other machines’ readings and was convinced I was pushing into high aerobic and low athletic levels with bursts up to my maximum (nominally an age-adjusted value). Going to maximum, even 90% of maximum, is potentially very dangerous but I have a long base (2.5+ years) of exercise, plus monitor BP (which is on low side of normal, previously had been high years ago before starting exercise and also using meds). For maximum safety one should actually have a stress EKG which I happen to have had for a surgery recently. So it’s safe for me to push as hard as I can.

So here’s my findings:

1. the maximum intensity I can get to on treadmill just barely reaches the aerobic range
2. the maximum intensity on treadmill is actually at 7.5 degree incline and 3.1 MPH and the 15 degree incline at 2.8MPH I normally do is actually LOWER in measured heart-rate. It appears that holding on the support bar, as I have to do at the higher incline, significantly reduces workout intensity. The actual maximum intensity was 118BPM.
3. the standard elliptical workout I do gets me considerably higher, to about 135BPM and with the maximum intensity sprints (that I started doing a few months ago) kick up to 148BPM, but I can only sustain those about 40-60 seconds (level 11, 4.2MPH). So the routine elliptical exertion is higher than the highest I can get on treadmill.
4. the reading of calories on elliptical (converted to calories/minute) is considerably lower than treadmill, SO, treadmill calories formula is probably based on a usage pattern different than the exercise I’m doing (i.e. hands-off jogging). The relatively low intensity treadmilling (6 degree include, 2.5MPH – my “cruising” speed where I read and really put in the time is a very modest level of activity, where heart-rate measurement suggests even lower than the METs the machine calculates
5. the elliptical sensed the Polar belt but the readings it showed were nonsense (around 33% too high). At first I thought the wrist display might be the one in error (although I’d still have to use it for comparison across machines) but eventually I concluded the elliptical is too high. That probably has been the source of my belief I was doing much more intense workouts on the elliptical.
6. the bike, at “cruising” speed is not very intense (a bit higher than treadmill at cruising) but I could actually push maximum heart-rate measured higher on bike than I could on treadmill, but my perceived level of effort was very high. While my cardio intensity seemed a bit lower than the elliptical the fatigue level in my legs limited my exertion.

Now, in terms of the possibility of habituation to the machines, I have gotten far more adapted to treadmill (for a long time the only machine I had). I’ve done 700 or so miles (in the last measured exercising, probably at least another 500 miles before that in earlier sessions) whereas I’ve only done about 200 miles on elliptical. Clearly treadmill and elliptical exercise different muscles. While I’ve gotten quite a few miles on bike (bicycling miles are never comparable, or need to be adjusted by roughly 5X, plus when I was on real bicycle I actually did do some centuries and the longest single day hike I ever did was 18 miles, so in shape I’d adjust by something more like 7X). Given that adjustment (or using time instead of miles) bike is still relatively new and it requires different muscles.

So what does this all means:

1. I still need more data to get calibration, but this is a start
2. My workouts (and thus calories burned) have not been as intense as I need and no wonder I compute weight-loss higher than it actually is because I’ve been drasticially over-estimating calories-burned
3. The low intensity workouts are fairly useless in terms of calories burned
4. I need to use elliptical more, use high intensity on bike more, go for more hands-off on treadmill.
5. I need to drastically reduce my perceived sense of getting lots of exercise based on long-duration, but low intensity treadmill
6. I need to watch my ankle problem as the high intensity stuff is almost pushing it too hard, but
7. I really need to get my bike and elliptical muscles as conditioned as treadmill muscles so I can do more quantity and intensity of workouts there.
8. I need to figure out which of these types of workouts will be the most sustainable after the focused program of weight loss is concluded.