Protocol summary
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Study aim
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Investigating the effect of caffeine, beetroot juice, and their combination on judo-specific performance in simulated conditions of the competition day in judo athletes
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Design
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A crossover, placebo-controlled, double-blind, randomized, phase 3 clinical trial on 35 judo athletes. The RAND function of Excel software will be used for randomization.
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Settings and conduct
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Each participant will participate in 4 experimental sessions (following BR, caffeine, caffeine plus BR, placebo), completing 5 trials in each session (4 min of randori plus SJFT plus CMJ test plus hand grip strength test plus cognitive function). The study will be double-blinded and will be conducted in Ankara, Türkiye.
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Participants/Inclusion and exclusion criteria
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Inclusion criteria: Must have at least a brown belt in judo; must not smoke; must not drink alcohol; must have a daily caffeine intake of less than 100 mg.
Exclusion criteria: Must have any injury or illness; must be taking any supplements or medications.
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Intervention groups
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1) Beetroot juice consumption (2 hours pre-exercise & immediately after the second trial, 70 ml each time);
2) Caffeine consumption (60 minutes pre-exercise and immediately after the third trial, each time 3 mg/kg of body weight);
3) Beetroot juice + caffeine consumption (beetroot juice: 2 hours pre-exercise & immediately after the second trial, 70 ml each time; caffeine: 60 minutes pre-exercise and immediately after the third trial, each time 3 mg/kg of body weight);
4) Placebo consumption (consumption of nitrate-depleted beetroot juice and opaque capsules containing 250 mg of sucrose as a placebo on an identical schedule).
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Main outcome variables
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SJFT outcomes، Cognitive function
General information
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Reason for update
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Adding some secondary variables to evaluate possible mechanisms;
Using both sexes as subjects;
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Acronym
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IRCT registration information
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IRCT registration number:
IRCT20231004059615N5
Registration date:
2025-07-18, 1404/04/27
Registration timing:
prospective
Last update:
2026-01-18, 1404/10/28
Update count:
1
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Registration date
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2025-07-18, 1404/04/27
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Registrant information
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Recruitment status
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Recruitment complete
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Funding source
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Expected recruitment start date
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2025-07-23, 1404/05/01
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Expected recruitment end date
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2025-07-27, 1404/05/05
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Actual recruitment start date
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empty
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Actual recruitment end date
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empty
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Trial completion date
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empty
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Scientific title
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The effect of caffeine and beetroot juice supplementation on specific judo performance during simulated competition-day conditions in judo athletes
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Public title
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Effect of caffeine and beetroot juice supplementation on specific judo performance
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Purpose
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Other
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Inclusion/Exclusion criteria
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Inclusion criteria:
All male judokas between the ages of 18 and 30.
Have a training history of more than 5 years.
Have at least a brown belt in judo.
Do not smoke.
Do not drink alcohol.
Have a daily caffeine intake of less than 100 mg.
Exclusion criteria:
Have any illness or injury in the past 3 months
Take any medication or nutritional supplement in the past 3 months
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Age
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From 18 years old to 30 years old
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Gender
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Both
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Phase
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3
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Groups that have been masked
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- Participant
- Investigator
- Data analyser
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Sample size
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Target sample size:
24
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Randomization (investigator's opinion)
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Randomized
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Randomization description
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The names of the subjects will be entered in one column of Excel; in another column, each subject will be randomly assigned a number using the RAND function (=RAND()); then, the numbers will be sorted from smallest to largest; 25% of the subjects will receive Intervention 1 (caffeine supplement), 25% of the subjects will receive Intervention 2 (beetroot juice supplement), 25% of the subjects will receive Intervention 3 (caffeine + beetroot juice), and the remaining 25% will receive placebo. In the second to fourth sessions of the experiment, the subjects will be switched (for example, subjects who received Intervention 1 in the first session will be randomly assigned to Intervention 2, 3, or placebo in the second session).
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Blinding (investigator's opinion)
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Double blinded
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Blinding description
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The order in which the beetroot juice supplement or placebo was administered will be determined by one outside the study and will not be disclosed to participants or researchers until after the data analysis. Participants will also receive the supplements and placebo in a capsule (caffeine) and a bottle (beetroot juice) that are opaque and look similar. In addition, the color and taste of the placebo will be simulated by adding food coloring and flavoring to the supplement.
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Placebo
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Used
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Assignment
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Crossover
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Other design features
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Ethics committees
1
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Ethics committee
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Approval date
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2025-07-03, 1404/04/12
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Ethics committee reference number
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202507-01
Health conditions studied
1
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Description of health condition studied
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Improve exercise performance
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ICD-10 code
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ICD-10 code description
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Primary outcomes
1
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Description
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SJFT index
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Timepoint
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In the 6 stages after judo randori
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Method of measurement
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Using the following formula: SJFT index = HR0 + HR1 / total number of throws
2
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Description
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Cognitive function
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Timepoint
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At baseline and after SJFT
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Method of measurement
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Using the Psychomotor Vigilance Test
Secondary outcomes
1
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Description
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Number of throws
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Timepoint
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In the 6 stages after SJFT
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Method of measurement
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Counting the number
2
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Description
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Heart rate
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Timepoint
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In the 6 stages immediately at the end of SJFT and 1 minute after SJFT
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Method of measurement
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Using a Polar heart rate monitor
3
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Description
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Rate of perceived exertion
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Timepoint
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In the 6 stages after SJFT
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Method of measurement
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Using the Borg scale
4
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Description
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Jump height
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Timepoint
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In the 6 stages (pre-exercise and after SJFT)
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Method of measurement
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CMJ Test
5
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Description
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Muscular strength
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Timepoint
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In the 6 stages (pre-exercise and after SJFT)
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Method of measurement
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Isometric strength testing device for hand muscles
6
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Description
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Blood lactate
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Timepoint
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At baseline, pre-exercise, mid-exercise, pre-final SJFT and post-exercise.
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Method of measurement
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Via Enzyme-Linked Immunosorbent Assay
7
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Description
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Muscle oxygenation
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Timepoint
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During the final SJFT
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Method of measurement
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Near-infrared spectroscopy
8
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Description
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Blood glucose
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Timepoint
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At baseline, pre-exercise, mid-exercise, pre-final SJFT and post-exercise.
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Method of measurement
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Via hexokinase method
9
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Description
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Plasma nitrate and nitrite
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Timepoint
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At baseline, pre-exercise, mid-exercise, pre-final SJFT and post-exercise.
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Method of measurement
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Via chemiluminescence assay
10
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Description
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Blood caffeine
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Timepoint
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At baseline, pre-exercise, mid-exercise, pre-final SJFT and post-exercise.
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Method of measurement
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Via High-Performance Liquid Chromatography
11
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Description
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blood PH
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Timepoint
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At baseline and post-exercise
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Method of measurement
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Blood gas analyzer
Intervention groups
1
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Description
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Intervention group1: Beetroot juice supplement (BEET It Sport®; James White Drinks Ltd., Ipswich, UK); 2 days before the test: 2 servings, 70 ml each, containing approximately 6.4 mmol nitrate;1 day before the test: 2 servings, 70 ml each, containing approximately 6.4 mmol nitrate;Test day: 2 servings, 2 hours before the test and after the second randori, 70 ml, containing approximately 6.4 mmol nitrate.
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Category
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Other
2
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Description
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Intervention group 2: Caffeine supplement (Caffeine®, Olimp Laboratories, Poland); Test day: 3 servings, 1 hour before the test and after the second and fourth attempts, 2 mg/kg body weight each.
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Category
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Other
3
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Description
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Intervention group 3: Beetroot juice supplement (BEET It Sport®; James White Drinks Ltd., Ipswich, UK); 2 days before the test: 2 servings, each 70 ml, containing approximately 6.4 mmol nitrate; 1 day before the test: 2 servings, each 70 ml, containing approximately 6.4 mmol nitrate; Test day: 2 servings, 2 hours before the test and after the second attempt, 70 ml, containing approximately 6.4 mmol nitrate. Caffeine supplement (Caffeine®, Olimp Laboratories, Poland); Test day: 3 servings, 1 hour before the test and after the second and fourth attempts, 2 mg/kg body weight each
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Category
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Other
4
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Description
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Control group: Similar to the intervention condition, they will receive placebo (colored water instead of beetroot juice and a capsule containing cellulose instead of caffeine).
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Category
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Other
1
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Sponsor
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Grant name
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Grant code / Reference number
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Is the source of funding the same sponsor organization/entity?
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Yes
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Title of funding source
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INTERNATIONAL SCIENCE AND TECHNOLOGY UNIVERSITY
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Proportion provided by this source
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100
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Public or private sector
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Private
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Domestic or foreign origin
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Foreign
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Category of foreign source of funding
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Sponsor: country of origin
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Country of origin
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IR
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Type of organization providing the funding
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Persons
Sharing plan
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Deidentified Individual Participant Data Set (IPD)
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Yes - There is a plan to make this available
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Study Protocol
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Yes - There is a plan to make this available
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Statistical Analysis Plan
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Undecided - It is not yet known if there will be a plan to make this available
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Informed Consent Form
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Undecided - It is not yet known if there will be a plan to make this available
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Clinical Study Report
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Not applicable
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Analytic Code
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Not applicable
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Data Dictionary
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Not applicable
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Title and more details about the data/document
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All data collected during the study will be shareable after de-identifying the subjects.
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When the data will become available and for how long
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The data will be published after the extracted articles are accepted.
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To whom data/document is available
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All people
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Under which criteria data/document could be used
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All data collected during the study will be shareable after de-identifying the subjects. The requester will only be permitted to use the data for meta-analysis reviews.
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From where data/document is obtainable
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Corresponding author: Davar Khodadadi, Faculty of Physical Education and Sports Sciences, Islamic Azad University Central Tehran Branch, Tehran, Iran Email: davar.khodadadi@yahoo.com
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What processes are involved for a request to access data/document
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Sending an email request to the corresponding author: Davar Khodadadi Email: davar.khodadadi@yahoo.com
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Comments
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