As someone who's needed to lose 20 pounds for the last 20 years, I've never been a big fan of scales. Teller of truths, dasher of hopes, and sapper of motivation, the scale lies smug at your feet impassively displaying its readout as if to say: "What? They're just numbers." But they say so much more, don't they? Now there's a new scale from Withings that not only lets you know how much weight you didn't lose yesterday, but also measures the wave your heart makes in your arteries to make you feel extra bad about your cardiovascular health too. I tried it out and investigated Withings' claims.

If you're familiar with Withings, you know that they already make a scale called the Body that makes you feel miserable – erm, I mean motivated – by not only displaying your weight but also your fat, bone and muscle mass as well as your water content. Today, it announced a new version of that scale called the Body Cardio that adds a measurement called your pulse wave velocity or PWV.

Your PWV is a measurement of the pressure wave that travels down your arteries each time your heart beats. It's a good measurement of the flexibility and fitness of your overall cardiovascular system. The stiffer your arteries are, the higher the PWV and the greater your chance of cardiovascular issues like stroke, high blood pressure or heart attack.

While PWV is a well-established health marker, what hasn't been tested thus far is how good a scale could be at measuring it. Curious as to how a scale could even begin to measure waves in your arteries, I asked a company representative for more information. Here's what I was told:

Body Cardio measures pulse wave velocity based on the time it takes for a blood wave to flow from the aorta to blood vessels in the feet. Thanks to its sensors, Body Cardio detects slight weight variations on the scale caused by heart beats and senses the moment when blood is ejected from the aorta and the moment when it reaches blood vessels in the feet. The time between these two events is then compared to the user's height, and Body Cardio can compute the pulse wave velocity while you step on the scale in approximately 15 seconds.

Hmm, a scale that could sense "the moment when blood is ejected from the aorta?" Not only did that sound a little implausible to me, but it also felt a little creepy. Now, in addition to my scale silently mocking my lack of willpower in terms of my diet, it could also look inside my body. This was getting kind of personal.

What the experts say

To check out the company's claims, I sought out a few cardiovascular experts.

The first, Neal Weintraub, a professor of cardiology at Augusta University in Georgia feels the technology could be legitimate.

"I do believe this technology is feasible and appears to be based on the principles of ballistocardiography, a very old technique that detects slight body motions consequent to ejection of blood from the heart into the great vessels," Weintraub told me. "The sensor system would have to be very sophisticated to perform an accurate measurement in the standing position, as slight motions would cause artifacts."

Weintraub suggested I check with his colleague Ryan Harris for another opinion. Harris is the director of Augusta's Laboratory of Integrative Vascular and Exercise Physiology and he concurred with Weintraub, especially on the point that the scale would have to be extremely accurate, although he did have some caveats.

"I am more concerned with 1) determination of distance, and 2) the significance of aortic to pedal PWV," he said. "In order for an accurate assessment of PWV you need the exact distance between the two sites. Although entering height will give you a standard distance, a more accurate distance will need to subtract the distance from the top of the head to the aorta from the total height."

Harris also added that in his opinion, a much better measurement of PWV is taking the reading from the carotid artery in the neck to the femoral artery in the groin, rather than the measurement from the heart to the feet.

Lastly, I heard from Assistant Professor of Medicine at UCLA's cardiology center, Kim-Lien Nguyen, who offered the usual cautions in using a piece of technology to evaluate your health.

"Because surrogate measures of arterial stiffness are affected by a variety of environmental conditions, performance and interpretations of these measures require specialized training and are best done in consultation with a physician specialist," she said. "Diet, exercise, medical adherence, and regular doctor visits will likely have greater yield than monitoring one's day-to-day pulse wave velocity."

What this non-expert says

So that's what the experts say about the Body Cardio scale. What about the opinion of this very un-expert scale user?

First off, I found the scale to be very well made. It's heavy, yet thin, and exudes quality.

When the scale arrived, it require a bit of set-up through an accompanying app which took about 15 minutes in total. This included connecting the scale to my home's Wi-Fi network so that it could communicate its results to the cloud. It also required the establishing of a Withings account to track my data. To activate the scale's PWV functionality I had to walk through a process that had me step on it five times for calibration.

After that, weigh-ins are pretty straightforward affairs. When you step on the scale, corner arrows help you position yourself properly and then the readout delivers your weight, your gain or loss from the last time you stepped on it, your water percentage, the high and low temperature for the day, and your heart rate. The whole process takes about 30 seconds.

While you can see all of that data instantly, you have to wait about a minute or so until the information uploads to the server before you can view other stats like bone and muscle mass and PWV value on your phone. I found this peculiar and a little inconvenient. Why not allow the scale to read out all of the data on its display?

While I was able to eventually get the PWV functionality to work after a few false starts thanks to the beta version of the app, most of the times I used the scale, I kept getting a message stating that it wasn't able to calculate my PWV. It eventually gave me a reading that put me in the "normal" range, but that's a pretty frustrating glitch for a scale that touts such functionality as its stand-out feature.

There were also pretty significant fluctuations in my weight even when I stepped on the scale within seconds of a previous weigh-in. In the course of 15 minutes, it showed a 1.3 lb (0.6 kg) fluctuation in my weight with no two readings exactly the same over the course of seven weigh-ins. That definitely brings up some questions about its accuracy. If it can't consistently get my weight right, how good is it doing with the sensitive measurements relating to the opening and closing of my heart valve?

Another glitch I encountered with the product is that about once out of every eight or so weigh-ins, it simply couldn't give me a readout on my heart rate. I have no idea why, as I was often stepping on the scale immediately after having just gotten a reading, but there you have it.

Considering the accuracy issues and the problems with the PWV value – and the fact that the scale is retailing for US$179 – I'd be inclined to give it a pass. Like Dr. Nguyen said, the best way to get in shape is with that old boring couple of diet and exercise. At least that'll spare you from having a judgy scale at your feet.

The Body Cardio is for sale in all Apple stores and on the Withings website. The company's commercial for the scale explaining how it works can be viewed below.

Product page: Withings

View gallery - 4 images