Body movement distribution with respect to swimmer's glide position in human underwater undulatory swimming

Human swimmers use undulatory motions similar to fish locomotion to attain high speeds. The human body is a non-smooth multi-body linkage system with restricted flexibility and is not primarily adapted to motion in the water. Due to anatomical limitations, the human swimmer is forced to deviate from the symmetric fish-like motion and to adjust his motion to his limited abilities. The goal of this paper is to investigates the movement of ten swimmers during human underwater undulatory in a still water pool and to find out to what extent the human swimmer approaches an ideal undulatory wave which is symmetric with respect to the extended gliding position. Therefore, it is necessary to (i) to ascertain the magnitude of the normalized dorsal, ventral and total amplitudes of the undulatory movements, (ii) to examine the distribution and symmetry/asymmetry of the dorsal, ventral and total amplitudes along the length of the swimming body, and (iii) to compare the differences in amplitude distribution and other indicators between different skill levels. The amplitude distribution of the dorsal and ventral deflection along the body (related to the swimmer's stretched position) is highly asymmetric. Skilled swimmers swim with a more linear body wave and use a smaller range of envelop than less skilled swimmers. The durations of the up and down kicks show only minor differences. The down kick is slightly faster than the up kick. Although the down kick is more powerful than the up kick, the hip marker shows almost the same average swimming speed in both half-cycles.