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Swim drink study: a randomised controlled trial of during-exercise rehydration and swimming performance
  1. Graham L Briars1,2,
  2. Gillian Suzanne Gordon3,
  3. Andrew Lawrence4,
  4. Andrew Turner4,
  5. Sharon Perry4,
  6. Dan Pillbrow4,
  7. Florence Einstein Walston1,2,
  8. Paul Molyneux5
  1. 1 Paediatric Gastroenterology, Norfolk and Norwich University Hospital NHS Foundation Trust, Norwich, UK
  2. 2 Faculty of Medicine and Health Sciences, University of East Anglia, Norwich, UK
  3. 3 Community Paediatrics, Child Development Centre, Bury St Edmunds, UK
  4. 4 West Suffolk Swimming Club, Bury St Edmunds, UK
  5. 5 Neurology, Addenbrooke’s Hospital, Cambridge, UK
  1. Correspondence to Dr Graham L Briars; g.briars{at}


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

Design Randomised controlled multiple crossover trial.

Setting A UK competitive swimming club.

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

Interventions 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.

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

Masking Participants blind to drink allocation until session start.

Results 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)%.

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

Trial registration ISRCTN: 49860006.

  • exercise physiology
  • adolescent health
  • nutrition

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  • Contributors GLB designed and managed the study, analysed the data and wrote the manuscript. AL, AT and GSG designed and conducted the timing data collection strategy. SP and PM contributed to the planning and collection of subject data. DP designed the training regimes and contributed to the design of the study. FEW was the study randomiser. All authors contributed to the manuscript and approved the final manuscript. G John performed biochemical analysis on the study drinks. R Reading, P Clarke and members of the Medical Advisory Committee of the Amateur Swimming Association made helpful comments on the manuscript.

  • Competing interests None declared.

  • Ethics approval The study was approved by Faculty of Medicine and Health Sciences Research Ethics Committee at The University of East Anglia (Ref 2013/2014-55).

  • Provenance and peer review Not commissioned; externally peer reviewed.