**José M. Oliva-Lozano 1, Isabel Martín-Fuentes <sup>2</sup> and José M. Muyor 1,2,\***


Received: 10 February 2020; Accepted: 21 April 2020; Published: 22 April 2020

**Abstract:** To understand the physical demands of sexual intercourse, it is necessary to monitor the kinematic parameters of this activity using relatively non-invasive technology. The aims of this study are to analyze the validity and reliability of an inertial device for monitoring the range of motion at the pelvis during simulated intercourse and compare the range of motion (ROM). Twenty-six adults were monitored during intercourse using an inertial device (WIMU) and a motion capture system (gold standard) in a test that consisted of 4 sets of 20 simulated in–out cycles (IOC) in missionary and cowgirl positions. Men and women were tested separately in a laboratory setting for simulated intercourse aims. There were no differences between the WIMU and the gold standard system at fast pace (*p* > 0.05), whereas there were differences at slow pace (~2.04◦; *p* ≤ 0.05; *d* = 0.17). Intraclass correlation coefficients (ICCs) for the relationship between systems was very close to 1 at both paces (slow: 0.981; fast: 0.998). The test–retest reliability analysis did not show any difference between sets of measurements. In conclusion, WIMU could be considered as a valid and reliable device for IOC range of motion monitoring during sexual intercourse in missionary and cowgirl positions.

**Keywords:** sexual activity; posture; IOC; kinematics; WIMU
