Wednesday, March 17, 2010

Houston, We Have Lift-Off

I lost my Polar 720 HRM. Again. This is the third time. They don't make the 7xx series anymore. I'd get a newer version, but I have the Power Output Pod that goes with the 7xx series and the new CS HRMs from Polar aren't compatible. Besides that, there are alot of 720 HRMS out there that work fine, but have a broken strap or bezel, that people dump on ebay cheap.

So I did a bit of surfing (between my porn quests) and found a used 720 on craigslist for $100. It allegedly worked fine, but it was in fucking Utah. The woman selling it HRM had a Ph.D. in her sig, so I googled her because I like to see how full of shit people are. Turns out she has PH.D. in psychology, and is in clinical practice as well as academia (albeit exclusively in mormon enclaves). One site she contributes to notes she has six kids. So after a couple emails, I felt satisfied that it was legit (I mean, mormons aren't supposed to lie, right?) so I bought it.

So I get the thing, and it was exactly as advertised, very clean, 100% working. Excellent. I set the thing up for me, and notice there are a whole bunch of exercise files, so I download them. Each exercise had one weird characteristic. At the beginning of the excercise the altitude showed pretty close to Zero, then in 15 seconds it shoots up to 4700 feet.

That's a climb rate of 18,800 feet per minute. While it isn't exactly escape velocity, it _is_ an average speed of 213 MPH. Anyone care to calculate the power needed to move a human 4700 feet in 15 seconds, straight up (account for gravity _and_ air resistance)? Yes, the altitude function of the HRM _does_ work, as is shown in this plot from a run earlier this week:

So I emailed the previous owner and asked about it. I speculated that the owner may have been in an commercial air-conditioned space when they started the HRM, then went outside. The location of the previous owner was American Fork, UT, which is at 4600 feet. A commercial building with an appropriate air conditioning system would pressurize the building and could fool the barometric sensor in the HRM into thinking it was at sea level until he left the building.

This is the reply I got:

"That does sound quite amazing. I'm not familiar with the watch myself. It was my husbands who use to do triathlons. He passed away last year."


Lift-off, indeed.

So here I doubted the integrity of this woman by googling her credentials, find out she's legit, find out it belonged to her deceased husband, and she's taking care of the six kids by herself now.

I feel this big.


Amanda said...

but coming from the daughter of a widow, this was not the first time she's had to explain.

solobreak said...

I'll bet that is normal behavior for the Polar. We just never notice it here because the jump from 0 to 300 or whatever just blends in with the rest of the graph.

zencycle said...

Solo - That had crossed my mind, but the raw data doesn't bear that out. The dead guys initial altitude readings in the actual data files all start at 0. Every file I have (from this monitor and the previous one) starts out at whatever the monitor was sensing. For example, the second picture in the post in fact has an initial reading of 380 feet, and that is the same monitor, not my old one.