*2.1. Participants*

**Table**

**1.**

and

Fourteen regional and national level male and female swimmers (ten sprinters and four middle-distance swimmers) that specialized in competitive distances of 100, 200, and 400 m volunteered to participate in the study (Table 1). Participants had a training background of 9.9 (1.8) years and they participated in daily training (6 days per week) with a duration of approximately two hours per session. Participants were randomly selected from local swimming clubs after getting agreemen<sup>t</sup> from parents and coaches. Swimmers were not consuming nutritional supplements during the testing period; they were asked to consume the same diet two days before the trials. Participants were instructed to avoid alcohol or ca ffeine consumption two days before each testing session. Each participant and his or her legal guardian provided written informed consent after receiving thorough explanation of the study. The local institutional review board approved the experimental procedures (approval no: 1029/6/12/2017) in accordance with Helsinki declaration for human subjects.

 Anthropometrics performance characteristics of competitive swimmers. The are presented as mean values and standard deviation (*SD*) for both males and females and for each gender separately.

data


FINA: Fédération Internationale de NatationAmateur.

#### *2.2. Study Design*

Physiological and biomechanical parameters calculated during a progressively increasing speed swimming test (mean overall time: ~45 min) were compared to those measured during 30 min of continuous swimming. Swimmers were tested in two sessions 48 h apart (Figure 1), and all tests were completed at the same time of the day for each swimmer (between 14:00 to 16:00). Prior to the first testing session, body mass and height were measured (Seca, Hamburg, Germany). One day prior to the first testing session, as well as during the two days separating the two testing sessions, swimmers participated in an easy (BL: ~2 mmol <sup>L</sup>−1) low volume endurance training (~3000 to 4000 m). The study was conducted during the specific preparation mesocycle of training. All swimming tests were performed using front crawl in a 25 m indoor swimming pool with a constant water temperature of 25 ◦C to 26 ◦C and 60% ambient humidity.

**Figure 1.** Experimental design of the current study; 7 × 200 m: 7 repetitions of 200 m front crawl, h: hours.

#### *2.3. Progressively Increasing Swimming Speed Test and Parameters Calculation*

All swimmers participated in a standardized swimming warm-up, and 10 min later performed a 7 × 200 m front crawl test at intensities calculated using the most recent 200 m race time and corresponding to 60%, 70%, 75%, 80%, 85%, 90%, and maximum effort. Participants were familiarized with the pace of the first two repetitions during a previous training session. During testing, one of the experimenters walked alongside the swimming pool providing guidance during each 200 m repetition. During the 7 × 200 m test, each repetition started every five minutes and 30 s with a push-off start from within the water [1]. Fingertip blood samples were collected after each repetition and were analyzed for BL (Lactate Scout<sup>+</sup>, SensLab GmbH, Leipzig, Germany). Immediately after the completion of each 200 m repetition, a mouthpiece and a nose clip were attached to swimmers during recovery. Expired air collected during the first 20 s of recovery was analyzed for oxygen uptake (VO2) using a portable gas analyzer (VO2000, Med Graphics, Saint Paul, MN, USA.; [14]). HR was recorded continuously using telemetry (s610i; Polar Electro, Kempele, Finland). A vest was used to keep the transmitter attached to each swimmer's chest while swimming. sLT and the respective BL-sLT were calculated by the x-axis projection of the intersection of lines connecting the three higher and four lower points of the speed lactate curve (BL-sLT: mean *R*<sup>2</sup> = 0.97 (0.02), mean *r* = 0.99 (0.01); 1). VO2-sLT and HR-sLT were calculated by interpolation using linear regression of swimming speed versus VO2 (mean *R*<sup>2</sup> = 0.99 (0.02), mean *r* = 0.99 (0.01)) or HR (mean *R*<sup>2</sup> = 0.99 (0.01), mean *r* = 0.99 (0.01). During the 7 × 200 m test, SR was calculated by the time (T) used to complete three arm-stroke cycles (180·T−1) and SL was calculated by dividing swimming speed every 50 m (V) by SR. The time for three arm-stroke cycles was recorded using a handheld chronometer. SR-sLT and SL-sLT were calculated by interpolation using the best fit regression line of SR and SL versus swimming speed during the 7 × 200 m test (SR: mean *R*<sup>2</sup> = 0.98 (0.02), mean *r* = 0.99 (0.01); SL: mean *R*<sup>2</sup> = 0.96 (0.04), mean *r* = 0.98 (0.02)).

#### *2.4. Continuous Swimming Session with Constant Speed*

The swimmers participated in a continuous swimming session 48 h after the completion of the 7 × 200 m test. Continuous swimming speed session was completed after a standardized warm-up that consisted of 1000 m of swimming (400 m slow swimming at 60% intensity, 4 × 50 m front crawl kicks, 4 × 50 m front crawl drills, and 4 × 50 m front crawl swim with progressively increasing speed). Ten minutes after warm-up, the swimmers started a T30 at a constant speed corresponding to sLT. During T30, the swimmers kept the individual sLT speed constant while guided by a sound signal emitted by a transmitter placed next to the ear and under the swimming cap (FINIS tempo pro, Finis Inc., Livermore, CA, USA). The swimmers were instructed to adjust their speed in order to touch the wall at each sound signal. Additionally, one of the experimenters recorded the time for each 50 m split (HS-80; CASIO, Guangzhou, China). BL-T30 and VO2-T30 were measured after the 10th and 30th minute of T30, while HR-T30 was recorded continuously. SR-T30 and SL-T30 were measured every 50 m during the T30 continuous swimming session. The 10th min was used to identify variations in physiological adjustments compared to the 30th min. Nevertheless, the mean values of BL, HR, SR, SL, and speed (s-T30) measured during the T30 were used for the statistical analysis.

#### *2.5. Statistical Analysis*

The student *t*-test for dependent samples was used to examine the di fferences in physiological and biomechanical parameters calculated during the 7 × 200 m progressively increasing speed test and those measured in T30. Specifically, comparisons between sLT, BL-sLT, VO2-sLT, HR-sLT, SR-sLT, SL-sLT vs. s-T30, BL-T30, VO2-T30, HR-T30, SR-T30, SL-T30, respectively, were applied. Pearson *r* correlation coe fficient was used to examine the relationship between the calculated values from a 7 × 200 m test with that measured during T30. The e ffect size for paired comparisons using the pooled standard deviation as denominator was calculated with Cohen's *d* [15]. The e ffect size was considered trivial if the absolute value of Cohen's *d* was less than 0.20, small if it was between 0.20 and 0.50, medium if it was between 0.50 and 0.80, and large if it was greater than 0.80. The 95% confidence limits (95% CL) were also calculated for the mean di fferences between parameters. G-Power 3.1.9.4 software [16] was used to examine the power of analysis. Considering the sample size in the current study ( *N* = 14), an *ES* of 0.80 was required to ge<sup>t</sup> a statistical power value greater than 0.80. For the estimation of agreemen<sup>t</sup> between parameters, Bland and Altman plots were used [17]. SPSS software (v.23, SPSS Inc., Chicago, IL, USA) was used for data analysis. Data are presented as mean and standard deviation (SD). Statistical significance was set at *p* < 0.05.
