Apart from the well-known chest-belt technology (Garmin and Polar), I’d like to do a small introduction about WTEK sensor’s working principles. This interesting transducer is a photoplethysmograph, a complicate word for a simple function: it illuminates the skin and subsequently measures the changes in light absorption due to the pulsatile component of the cardiac cycle. In other words, it can measure the differences in blood volume, identifying this way the heart rate of the subject. This is an interesting feature, since the sensor can be applied to the forearm or to the forehead, simply using a sweatband as a support.
|How to fit the WTEK sensor (click to enlarge).|
|The altitude chamber, for the occasion set to sea level, before and during the test. I am wearing a wristband on my left forearm to support the WTEK sensor (click to enlarge).|
|The WTEK C100 watch, its charging station, a sensor and a wristband (click to enlarge).|
|Heart rate data (click to enlarge).|
- an initial period of 10 to 15 minutes is necessary to stabilise data
- every sudden change in heart frequency needs 10 to 15 seconds to be noticed by the sensor
- an overshoot (both negative or positive) always occurs when heart rate changes quickly, for example during interval training or hill repetitions.
- the errors, after the stabilisation period, are almost always included in a ±5% interval (taking as “real” values the average between Garmin and Polar data)
- correlation coefficients (degree of similarity between two sets of variables) are quite similar, being 0.9998 between Garmin and Polar, 0.9891 between Garmin and WTEK and 0.9889 between Polar and WTEK
- mean registered heart rate values are pretty close (152.8 bpm for Garmin, 152.7 bpm for Polar and 157.7 bpm for WTEK)
- usually the error causes an overestimation of the HR values (a dangerous underestimation happens very rarely).
|Absolute percentage error calculated between WTEK and the average of Garmin and Polar values (click to enlarge).|
|The WTEK products tested (click to enlarge).|
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