Three-dimensional Kinematic Analysis of Shoulder through Wearable Inertial and Magnetic Sensors during Swimming Strokes Simulation

Wearable inertial and magnetic measurement units (IMMUs) have recently gained much attention in investigations approaching human kinematic analysis in sports scenario. Running, tennis, baseball, snowboarding, rowing, and swimming are some examples of sports already approached. In swimming, many studies proposed several methods to identify the temporal phases of a single swimming stroke or the swimming style. However, this temporal information alone does not provide any joint kinematic data like joint angles. Therefore, the present study aimed to verify the accuracy of a protocol, previously developed for ambulatory joint kinematic analysis through IMMUs, in measure the shoulder kinematics during swimming strokes simulation. A stereo-photogrammetric system was considered the gold standard. Three trained swimmers realized 3 trials of breaststrokes simulation and 3 trials of front-crawl strokes simulation in dry condition. As first verification, the relative motion of both the segments thorax and arm with respect to the first-synchronized frame (automatically detected by an ad-hoc algorithm) was compared by means of root mean square error (RMSE) and correlation coefficient (r) between the two systems. The RMSE was 5° and 7°, and the r was 0.85 and 0.91 for breaststroke and front-crawl stroke, respectively, indicating a good relationship between both methods in measuring the body segments’ orientation. As second verification, the shoulder flexion/extension, abduction/adduction and internal/external rotation angles were computed, and no significant difference was found (p<0.05) between both systems. In conclusion, a protocol previously implemented for joint measurement in ambulatory settings is also suitable and accurate to estimate the shoulder kinematics during swimming strokes simulation when using wearable inertial and magnetic measurement units.