VALIDITY AND RELIABILITY OF THE WIRELESS PRESSURE SENSORS FOR AQUATIC ACTIVITIES AND THEIR ECOLOGICAL USEFULNESS FOR SWIMMING PROPULSION ANALYSIS

INTRODUCTION The thrust force (Ft) is only a fraction of the overall force exerted by the swimmer to move his body. In the last decades, the hand pressure measurement technique has been implemented to support the understanding of Ft mechanism. However, because the direct assessment during free swimming remains difficult to quantify, the Ft measurement during tethered swimming was proposed as an alternative method. Furthermore, the advances in wireless technology could help the knowledge about swimming propulsion using an ecological approach and lower interferences with the swimming action than the wired sensors. Thus, the aims of this study were: i) to test the within-sensor, between-sensor and day-by-day reliability of the device, ii) to test the device in terms of accuracy than theoretical static (PRsT) and dynamic (PRdT) pressures, iii) to compared Ft between the differential pressure approach (FtHAND) and the dynamometrical approach (FtTET) during fully-tethered swimming. METHODS Static pressure (PRs) collected by the wearable pressure sensor (SEAL, Platysense) was compared to PRsT (𝑃𝑅𝑠𝑇=𝑃𝑎𝑡𝑚+𝜌𝑔ℎ) through a step static immersion up to 50 cm. Dynamic pressure (PRs) was compared to PRdT (𝑃𝑅𝑑𝑇=0.5𝜌𝑣2) by towing 4 SEALs using a towing system at constant velocities (V) of 1.0, 1.6, and 1.9 ms-1 and controlling the water depth. The resultant force exerted by each hand to move the water (FHAND) of 15 young swimmers (7 F, 75.5 ± 7.1 % of WR) was the product of differential hand pressure (palmar minus dorsal, PRDIFF) and the hand surface (A). Ft exerted by the hand to propel the body (FtHAND) was the FHAND horizontal component and was estimated as Fhand . sin(α), where α was the underwater angle between trunk and upper arm (assuming circle-shaped hand kinematics). FtTET was the average value of the 10-s maximal effort in front-crawl. RESULTS PRs showed excellent agreement for within-sensor, between-sensor and day-by-day reliability regarding ICC (0.99, 0.99, 0.99) and CV% (<0.1, <0.08, <0.13). Small biases and no-differences (p < 0.05) were detected for PRs vs. PRsT (<0.13 KPa) and for PRd vs. PRdT (-0.11, -0.26, -0.21 KPa, for each V comparison). PRDIFF was 4.678±1.123 Kpa, A was 0.015± 0.001 m2 and stroke frequency was 0.91 ± 0.06 Hz. FtHAND (51.6±17.0 N) was positively correlated (r=0.904, p<0.001) with FtTET (80.4±15.9 N) but significantly lower (p<0.001). DISCUSSION PRs and PRd acquired using wireless pressure sensors showed a small amount of error when compared to theoretical pressures (<0.4 %) which represents a maximum error of 7.8 N in FtHAND value. The swimmer’s thrust force estimated using this approach is lower than the force collected by the dynamometrical approach during fully-resisted swimming (-41%). This difference could be partly imputable to the contribution of the forearm.