Repeated sprint exercise has been used as a training method [usually referred as sprint interval training (SIT)], as it is time-efficient and capable of inducing similar or even superior adaptations
on the cardiorespiratory system than continuous endurance training. Furthermore, SIT involves powerful muscle contractions, approximating competitive tasks of many athletes, such as short-distance
swimmers, which may be an important factor to elicit neuromuscular adaptations. Of note, physical performance progressively decreases during a SIT set. Thus, it is possible that fatigue during a SIT
set changes the swimming kinematics, which remains unknown. Accordingly, the aim of this study was to describe the swimming kinematics during a SIT set in swimming.
Twenty-two (6 females and 16 males) short-distance university swimmers were enrolled. They had been training in the same team, for at least 5 years. The protocol encompassed 2 visits per subject. The
first visit was used to measure the time to complete a single 50-m maximal effort from a push start. The repeated sprint swimming task was performed in an indoor pool, 50-m long. Subjects performed 15
min of warm-up. Then, performed a SIT task that consisted of 6 sprints of 50 m at maximal effort repeated every 3 min. Sprints started from a push start, to avoid technical variations involved in
jumping off the start block. Subjects were instructed to swim as fast as possible throughout the set, since the beginning of each sprint. To avoid a "pace" strategy during the set, the first sprint
had to be within at least 95% of the time achieved during the familiarization visit. The following parameters were obtained from the set: rate of perceived exertion (RPE), sprints time [best time (BT;
i.e., lowest sprint time, which was always the first sprint), total time (TT; time sum of six sprints), and percent decrement (%DC)]. Swimming kinematics consisted of assessing stroke rate (SR),
percent decrement of the stroke rate (%SR), best stroke rate (BSR) and stroke length (SL) at the middle of the pool, as well as the total number of breaths (NB) and swimming velocity (SV).
Sprints time, NB and RPE increased over the sprints (P < 0.05). SR decreased in the 2nd and 3rd sprints (P < 0.05 vs. 1st sprint) and then was maintained until the last sprint. SV decreased over the
sprints (P < 0.05). SL were similar among the sprints (P = 0.25). There was a large correlation between BT and BSR (r = - 0.5; P = 0.01), and a very large correlation between %DC and %FB (r = - 0.7; P
In conclusion, this study showed that the fatigue gradually increases during a SIT, which reflect in the increase of the NB and in the decrease of the SR. Thereby, the increase in sprints time was
associated with the increase in SR.