No abstract

The underwater phase of starts represents an important part of the performance in sprint swimming’s events. Kinematics variables that swimmers have to take into account to improve their underwater phase of starts are unknown. The aim of this study was to determine the kinematics variables that improve performance during the underwater phase of grab starts. A three-dimensional analysis of the underwater phase of ten swimmers of national level was conducted. Stepwise multiple linear regressions identified the main kinematics variables that influence the horizontal velocity of the swimmer each 0.5 m in the range of 5 to 7.5 m. The results show that the kinematics parameters change during the range of 5 to 7.5 m of the underwater phase of the starts. For this population of swimmers, the results enable proposals of four principles to improve the underwater phase: i) to be streamlined at the beginning of the underwater gliding phase, ii) to start the dolphin kicking after 6 m, iii) to generate propulsive forces using only feet and legs during underwater undulatory swimming, iv) to improve the frequency of underwater undulatory swimming.

The purpose of the present work was to study swimmers’ efficiency during the underwater phase of the grab start. Eight high-level swimmers participated in this study. They performed two types of start: a regular grab start (with underwater leg propulsion after the glide) and a grab start with no underwater movement (swimmers had to remain in a streamlined position). Four cameras filmed the entire underwater phase of all starts. Nine anatomic landmarks were identified on the swimmers’ bodies and their positions were calculated using a modified double plan DLT technique. From these positions and Dempster’s anthropometric data, the center of mass position and velocity were also determined. Kinetic energies were also calculated. This velocity and kinetic energies for the two types of start were compared. Swimmers began underwater leg propulsion 1.69 m too soon. The global and internal energies were significantly higher for the start with underwater leg propulsion. Nevertheless, swimmers’ velocities were equivalent for both starts. These results suggest that the swimmers did not use the underwater phase of the start efficiently: By kicking too soon, they did not succeed in producing higher velocities and thus wasted energy.

The purpose of this study was to analyse the effect of swimmer specialty on energy cost and motor organization. The stroking parameters (velocity, stroke rate, stroke length, stroke index) and the index of coordination (IdC) of 6 elite sprinters were compared with those of 6 elite long-distance swimmers during an incremental swimming exercise test (6×300 m separated by 30 s of passive recovery) that progressively increased the energy cost. Energy cost (C), with its aerobic (Caero) and anaerobic (Canaero) components, was determined by measuring oxygen uptake (VO2) and blood lactate ([La]). Motor organization was assessed by analysis of video recordings from aerial and underwater side-view cameras. The results showed that throughout the test, both groups increased C, Canaero, stroke rate and IdC and decreased Caero and stroke length (all P<0.05). On the mean of the 300-m sets, sprinters had higher values for C (14.8 vs. 12. For the same relative intensity, sprinters accumulated more lactate and swam more slowly than long-distance swimmers; they showed greater change in their arm coordination but their swimming economy was lower.

Swimmers' health maintenance requires particular attention when autonomic balance shows a sudden increase in parasympathetic indices in the supine position assessed 1 wk earlier evolving toward sympathetic predominance in supine and orthostatic positions.