The contribution to total race distances of underwater undulatory swimming (UUS) is increasing at the elite level. However, little is known about the technical modifications during underwater swimming. In the present research, the aim was to compare the kinematic characteristics of competitive swimmers between the first and last kick of UUS. Fifty-four national level swimmers (26 males and 28 females) performed 25 m maximal efforts from a push start, and two sequential video cameras captured the underwater segment. Kicking parameters and segmental kinematics were calculated by means of two-dimensional direct linear transformation algorithms. Dolphin kick performance showed a clear impairment in velocity (η² : 0.65), but changes on kicking parameters depended on the swimmer’s gender, with males decreasing kicking amplitude (η² : 0.25) and females decreasing kicking frequency (η² : 0.18) in the last kick. Decline in kicking performance seemed to be more related to the swimmers’ body configuration when approaching the water surface (greater trunk inclination and maximal body amplitude in sagittal plane) than to technical modifications in the dolphin kick movement (no changes in the joints range of movement except the hip). Swimmers should control their vertical body amplitude at the end of underwater sections to minimise the decrease in kicking performance.

The purpose of the present study was twofold: (i) to compare the kinematic characteristics of individual and relay swimming starts; and (ii) to relate the kinematic variables to 5 m performance for both starts. Twelve elite-level swimmers performed 2 × 25 m at maximal effort (one with an individual and one with a relay start randomly). Two-dimensional direct linear transformation algorithms were used to calculate swimmers’ centre of mass (CM) kinematics during each subphase. The results indicated moderate to much faster 5 m, 10 m 15 and 15 m times (29.4, 10.7 and 6.5%) for relay than individual starts as well as the differences at specific parameters, but no differences in take-off horizontal velocity between start techniques. Large correlations to performance times were found in block time, horizontal take-off velocity, take-off velocity and entry angle (r = 0.77 to 0.83) 20 for individual start, but in changeover time, take-off height and entry distance (r = 0.69 to 0.90) for relay start. Differences on swim start regulations between individual and relay events were in line with different key parameters related to start performances in each event. This should be considered by swimmers and coaches when addressing the starting improvement.

Backstroke swimmers display the greatest contribution of underwater kicking during the swimming race distances, but, surprisingly, there is little evidence of how kicking kinematics in the dorsal position should be performed. The aim of the present study was to examine the kinematic characteristics of competitive swimmers during underwater undulatory swimming in the dorsal position, with special attention to the swimmers’ gender, the level of skill, and kick order. Forty-one national-level swimmers (27 females and 14 males) were filmed from an underwater lateral view while performing a 25-m backstroke from a push start, and they were divided into fast and slow groups according to their kicking velocity. Direct linear algorithms were employed to reconstruct the two-dimensional kinematic characteristics of the first and final kicks of the underwater section. There were no differences between males and females in kicking performance when data were normalised to the swimmers’ height. However, swimmers in the fast-kicking group were distinguished by a greater kicking frequency (η²: 0.15) and specific segmental kinematics related to a lower knee range of motion. Swimmers decreased kicking velocity (η²: 0.47) in addition to the kicking frequency (η²: 0.31) and length (η²: 0.16), but increased the kicking amplitude (η²: 0.11) between the first and the final kicks. Changes in kicking segmental kinematics were more related to modification in body orientation during the underwater trajectory than to the kicking motion itself. These results provide the first solid evidence of how swimmers should kick for better performance in dorsal underwater swimming.

In swimming relay races, various start techniques are performed by swimmers, but it remains unclear which technique leads to a better start performance. Therefore, the purpose of the present study was to compare the kinematic characteristics of different relay start techniques with the new starting block Omega OSB11. Eleven international youth swimmers were filmed during 1) no step with parallel feet, 2) no step with separated feet and 3) one-step starts and their centre of mass kinematics calculated with 2D-DLT algorithms. Results indicate that differences between techniques were detected in the spatiotemporal parameters of the block and aerial start phases (e.g., initial and take-off positions, entry height, preparation and changeover times) and in selected parameters of the underwater phase (e.g., emersion time and distance, underwater time and distance). However, no statistical effects were found in 5 m, 10 m and 15 m start times, nor in horizontal take-off velocity, despite an observed trend for the one-step start to be superior to the non-step techniques. These results suggest that differences between relay techniques could rely more on the swimmer’s body posture (angular kinematics) on the block, flight and underwater phases than on the centre of mass linear kinematics.

The present study investigated swimmers’ performances on the starting and turning segments between individual and relay races. A total number of 72 race performances of the same swimmers in both relay 4 × 100 m finals (freestyle, medley, and mixed freestyle) and individual 100 m finals or semi-finals (butterfly, breaststroke, and freestyle) from the LEN European Swimming Championships were compared with repeated measures MANOVA. Swimmers performed 5–7% faster starts in the relay than in the corresponding individual events, despite no differences in the flight phase and a lower performance (shorter distances and slower velocities) on the underwater start section. The 15 m turn times were slower in the butterfly relay races although no specific differences in the underwater parameters were observed. These results suggest that specific training of the starting and turning segments should be performed under relay conditions to optimise pacing and performance in the underwater sections.

Despite the mechanical advantage of preparatory movements on the starting block, current evidence questions the start improvements of competitive swimmers with their relay techniques. Therefore, the aim of the present study was to analyse the kinetic and kinematic parameters of a successful relay start. Twenty national- and international-level swimmers performed several relay starts (n = 145) with their preferred technique (short or long-step start) over an instrumented OBS11 starting platform. Trials were classified as successful or non-successful depending on the 10-m times being faster or slower than their individual start. Linear Mixed Models outlined that successful relay starts were characterised (all p < 0.05) by a later (0.04 s) onset of the leg step, a lower (18%) horizontal force during the leg step, and a later (0.03 s) positioning of the hands at the lowest point of the upper-limb backswing. In addition, greater values for the maximal horizontal (12%) and vertical (9%) forces and faster horizontal (4%) and resultant (3%) velocities were detected when driving off the block. These characteristics were also dependent on the relay technique. Unlike individual track starts, swimmers with fast relay starts employed longer preparatory movements on the block to maximise the time of force application and thus the impulse.