The paper uses the SenseWear armband for estimating energy expenditure in sexual activity (SA). The validity of the SenseWear to estimate energy expenditure has been investigated in a number of scientific publications as the authors correctly state. However, none of those publications investigated the validity of the SenseWear to estimate energy expenditure in sexual activity (SA). The key question here seems to be: Can we extrapolate the published findings on validity in activity types like walking and running to a not yet validated activity type like SA?

In my opinion the answer is "No". The SenseWear relies on a set of sensors including a temperature-, galvanic skin response-, and movement-sensor. The way in which the resulting data coming out of these sensors is used for estimating energy expenditure is hidden from the user by proprietary software. New experimental conditions like SA can, in theory, pose a unique combination of temperature, galvanic skin response and body movement for which this proprietary algorithm has not been trained. As a result this may lead to activity type specific measurement bias. Consequently, evidence of activity type specific measurement validity seems essential before we can interpret any of these findings.