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BMJ Paediatr Open. 2017 Oct 25;1(1):e000075. doi: 10.1136/bmjpo-2017-000075. eCollection 2017.

Swim drink study: a randomised controlled trial of during-exercise rehydration and swimming performance.

Author information

Paediatric Gastroenterology, Norfolk and Norwich University Hospital NHS Foundation Trust, Norwich, UK.
Faculty of Medicine and Health Sciences, University of East Anglia, Norwich, UK.
Community Paediatrics, Child Development Centre, Bury St Edmunds, UK.
West Suffolk Swimming Club, Bury St Edmunds, UK.
Neurology, Addenbrooke's Hospital, Cambridge, UK.



To determine whether during-exercise rehydration improves swimming performance and whether sports drink or water have differential effects on performance.


Randomised controlled multiple crossover trial.


A UK competitive swimming club.


19 club-level competitive swimmers, median age (range) 13 (11-17) years.


Subjects were scheduled to drink ad libitum commercial isotonic sports drink (3.9 g sugars and 0.13 g salt per 100 mL) or water (three sessions each) or no drink (six sessions) in the course of twelve 75 min training sessions, each of which was followed by a 30 min test set of ten 100 m maximum-effort freestyle sprints each starting at 3 min intervals.

Main outcome measure:

Times for the middle 50 m of each sprint measured using electronic timing equipment in a Federation Internationale de Natation (FINA)-compliant six-lane 25 m competition swimming pool.


Software-generated individual random session order in sealed envelopes. Analysis subset of eight sessions randomly selected by software after data collection completed.


Participants blind to drink allocation until session start.


In the analysis data set of 1118 swims, there was no significant difference between swim times for drinking and not drinking nor between drinking water or a sports drink. Mean (SEM) 50 m time for no-drink swims was 38.077 (0.128) s and 38.105 (0.131) s for drink swims, p=0.701. Mean 50 m times were 38.031 (0.184) s for drinking sports drink and 38.182 (0.186) s for drinking water, p=0.073. Times after not drinking were 0.027 s faster than after drinking (95% CI 0.186 s faster to 0.113 s slower). Times after drinking sports drink were 0.151 s faster than after water (95% CI 0.309 s faster to 0.002 s slower). Mean (SEM) dehydration from exercise was 0.42 (0.11)%.


Drinking water or sports drink over 105 min of sustained effort swimming training does not improve swimming performance.

Trial registration:

ISRCTN: 49860006.


adolescent health; exercise physiology; nutrition

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