Thirty-two competitive national standard swimmers provided written informed consent to participate in this study approved by the University of Brighton SASM Research Ethics Committee with experimental procedures conducted in accordance with the Declaration of Helsinki, except for prior registration in a database. Participant characteristics are presented in Table 1. All participants met the selection criteria of being 16 years or older and having achieved a 2018 British Swimming Championships qualifying or consideration time.
Table 1. Participant characteristics
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Butterfly (n=7)
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Backstroke (n=8)
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Breaststroke (n=7)
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Front crawl (n=10)
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Age (yr)
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19 ± 2
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18 ± 2
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18 ± 2
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17 ± 2
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Sex (male/female)
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4/3
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6/2
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4/3
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6/4
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Height (cm)
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174.5 ± 7.9
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179.2 ± 9.3
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174.4 ± 8.3
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178.7 ± 7.9
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Body mass (kg)
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68.2 ± 8.2
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71.3 ± 9.7
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65.5 ± 5.0
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66.8 ± 7.6
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Urine osmolality (mOsm.l-1)
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740 ± 244
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642 ± 332
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692 ± 278
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662 ± 229
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Short/middle/long distance specialism
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5/2/0
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3/5/0
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3/4/0
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5/4/1
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Main event PB FINA point equivalent
|
749 ± 61
|
719 ± 107
|
784 ± 74
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718 ± 73
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Individual medley swimmers
|
1
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2
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1
|
0
|
Over the course of three weeks, participants were required to perform three 200-m and three 400-m performance trials separated all by at least 48 hours, with the order assigned using block randomisation (http://www.randomization.com). Trials were completed in each swimmer’s specialist stroke; individual medley swimmers chose whether to swim butterfly, backstroke, breaststroke or front crawl. To minimise circadian variations in performance22, participants performed all their performance trials at the same time of day. Performance trials were completed in a 25-m pool from a dive start following a standardised 1km warm up. To maximise performance, participants were permitted to eat and drink as desired in the 24 hours prior to the first trial, this intake was then standardised across all subsequent performance trials. Participants provided a urine sample before each trial for the assessment of urine osmolality (Osmocheck; Vitech Scientific, Horsham, United Kingdom). No feedback was given during or immediately after the performance trials, each participant received summary reports of their performance trials once all testing has been completed.
Prior to testing, lane ropes were fixed using 5mm stainless steel lane rope clamps (WRST-05; S3i Group, Doncaster, United Kingdom) and calibrated using Class III Accuracy 50-m measuring tape (Surveyors Tape; Draper Tools, Chandler’s Ford, United Kingdom). Each swim was recorded on a video camera (HC-X1000; Panasonic, Osaka, Japan) with analysis of lap splits performed retrospectively using proprietary analysis software 23. Height (cm) and weight (kg) were measured using a wall-mounted stadiometer (Harpenden Stadiometer; Holtain Limited, Crymych, United Kingdom) Hamburg, Germany) and flat scales (876; SECA, Hamburg, Germany) respectively by a Level 1 International Society for the Advancement and Kinanthropometry certified practitioner.
Having completed all performance trials, participants were asked to respond via e-mail to two questions with either a “Yes” or “No” answer: (1) “Could you have completed a full 800m effort in your stroke?”; (2) “Would you want to swim a 200-m, 400-m and 800-m effort over three separate days in order to have a measure of your critical speed and D’?”
Statistics
The SPSS software package (version 24, SPSS, Chicago, IL) was used for statistical analysis with data presented as means ± SD unless otherwise stated. Outliers and normality of distribution were examined using boxplots and the Shapiro-Wilks test respectively. Outliers were windsorized to the next highest value prior to further analysis. Violations of normality were kept in and are reported in the results section. A one-way repeated measures ANOVA was used to assess differences between the three trials. Sphericity was checked using Mauchly’s test, when the assumption of sphericity was violated significance was examined using Greenhouse-Geisser correction. Bonferroni correction was performed for all post-hoc analysis where the assumption of sphericity was not violated. Supplementary statistical data is presented in Appendix 1.
A published spreadsheet was used to calculate typical error of measurement (TEM), a measure of absolute test-retest reliability (Hopkins, 2007). TEM was divided by the trial mean and multiplied by 100 to calculate coefficient of variation (CoV). Smallest detectable individual change (SDCind) and smallest detectable group change (SDCgroup) values were calculated from mean TEM to 95% probability using equations 1 and 2, respectively. The smallest worthwhile change (SWC) was calculated by dividing between-subject SD values by 0.2.
Relative reliability was assessed through intra-class correlation coefficient (ICC) estimates and their 95% confidence intervals were calculated based on a single-rater, absolute agreement, two-way mixed effects model (ICC 2,1).24 ICC values < 0.50 were considered indicative of poor reliability, 0.50-0.74 considered moderate reliability, 0.75-0.89 considered good reliability and ≥ 0.90 considered excellent reliability.24A Fisher’s exact test was performed to assess responses to follow-up questions regarding the feasibility of an 800-m performance trial.