An interventional study of Caffeine and Placebo in Caffeine, Exercise and Physical Fitness, sponsored by Birjand University of Medical Sciences. Completed at 1 site in Iran. Open to female participants aged 18 Years to 30 Years, including healthy volunteers. Per ClinicalTrials.gov, last updated 2026-08-18.
Sponsored by Birjand University of Medical Sciences · Not applicable, Interventional, and Basic science
This study investigated the effects of a 7-day caffeine supplementation on heart rate variability, cognitive performance, and upper-body anaerobic power in active women. Thirty healthy active women aged 25-30 years participated in this double-blind, placebo-controlled trial. Participants were randomly assigned to receive either 5 mg/kg of caffeine or a placebo daily for 7 days. Heart rate variability, cognitive function (measured by the Stroop test), and upper-body anaerobic power (measured by a 20-second Wingate test) were assessed at baseline, 90 minutes after supplementation, and 30 minutes after exercise. The primary outcome was peak anaerobic power. The study aimed to determine whether short-term caffeine habituation enhances exercise performance without altering cardiac autonomic function or cognitive performance.
This was a double-blind, placebo-controlled, parallel-group study conducted at the University of Birjand, Iran. Thirty active women (aged 25-30 years, BMI 18-25 kg/m²) were randomly assigned to either a caffeine group (n=15) or a placebo group (n=15). Participants received 5 mg/kg of caffeine powder or placebo (flour) in gelatin capsules daily for 7 days.
Heart rate variability (HRV) parameters including RMSSD (Root Mean Square of Successive Differences), SDNN (Standard Deviation of Normal-to-Normal Intervals), LF (Low-Frequency) power, HF (High-Frequency) power, and LF/HF ratio were measured using a Polar H10 heart rate sensor. Cognitive performance was assessed using the Golden Stroop Test (color-word interference task). Upper-body anaerobic power was measured using a 20-second Wingate test on a cycle ergometer (Monark 891 E) with a workload of 50 g/kg body weight.
Measurements were taken at three time points: baseline (after 10-hour overnight fast), 90 minutes post-ingestion, and 30 minutes post-exercise. The protocol was repeated after 7 days of daily supplementation. Data were analyzed using repeated-measures ANOVA with Bonferroni post-hoc tests. The primary outcome was peak power output (W·kg-¹) during the Wingate test. Secondary outcomes included HRV parameters, cognitive performance scores, and other anaerobic performance indices (mean power, minimum power, fatigue index).
9,798 studies on the registry are indexed under Motor Activity; 1,910 are open to participants now.
This study's enrollment of 30 is below the median of 60 across 8,388 interventional studies indexed under Motor Activity.
Browse Motor Activity studies →Birjand University of Medical Sciences is the lead sponsor of 7 studies on the registry; 1 is open to participants now.
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Active women aged 25 to 30 years
(BMI) between 18 and 25 kg/m²
Physical activity readiness (based on the PAR-Q questionnaire)
No injuries within the last month
Non-smoking
No cold or COVID-19 infection in the past four weeks
No cardiovascular, metabolic, or respiratory infections in the last three months
Normal blood pressure
No use of anabolic steroids, central nervous system stimulants, or other sports supplements in the past six months
Exclusion Criteria:
Inability to follow the protocol
Daily caffeine intake exceeding 300 mg (assessed using an adapted FFQ)
Consumption of alcohol or intense aerobic activity within 48 hours prior to testing
Resistance training with weights within 72 hours prior to testing
Caffeine consumption within 24 hours prior to testing
Underlined terms in the criteria open these too. Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Weight in kilograms divided by height in metres squared. Example: 70 kg and 1.75 m gives 70 ÷ (1.75 × 1.75) ≈ 22.9.
What counts as overweight or obesity differs between countries (some use lower cut-offs), so go by the range the study states.
BMI (body mass index)
Weight in kilograms divided by height in metres squared. Example: 70 kg and 1.75 m gives 70 ÷ (1.75 × 1.75) ≈ 22.9.
What counts as overweight or obesity differs between countries (some use lower cut-offs), so go by the range the study states.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
5 mg/kg of body weight of caffeine powder in a gelatin capsule, ingested daily for 7 days.
Dietary Supplement: Caffeine
Participants received a matching placebo capsule containing flour, ingested daily for 7 days.
Dietary Supplement: Placebo
5 mg/kg of body weight of caffeine powder in a gelatin capsule, ingested daily for 7 days.
Matching placebo capsule containing flour, ingested daily for 7 days.
Change in Upper-Body Peak Anaerobic Power
Peak power output (W·kg-¹) measured during a 20-second upper-body Wingate test on a cycle ergometer (Monark 891 E).
Time frame: Measured 90 minutes post-ingestion on Day 1 and Day 7.
Change in Cognitive Performance
Cognitive performance assessed using the Golden Stroop Test (color-word interference task). The score represents the number of correct responses in the third part of the test (incongruent condition) within 45 seconds.
Time frame: Measured at baseline, 90 minutes post-ingestion, and 30 minutes post-exercise on Day 1 and Day 7.
Change in RMSSD
Root mean square of successive differences (ms) measured using a Polar H10 heart rate sensor.
Time frame: Measured at baseline, 90 minutes post-ingestion, and 30 minutes post-exercise on Day 1 and Day 7.
Change in SDNN
Standard deviation of normal-to-normal intervals (ms) measured using a Polar H10 heart rate sensor.
Time frame: Measured at baseline, 90 minutes post-ingestion, and 30 minutes post-exercise on Day 1 and Day 7.
Change in LF Power
Low-frequency power (ms²) measured using a Polar H10 heart rate sensor.
Time frame: Measured at baseline, 90 minutes post-ingestion, and 30 minutes post-exercise on Day 1 and Day 7.
Change in HF Power
High-frequency power (ms²) measured using a Polar H10 heart rate sensor.
Time frame: Measured at baseline, 90 minutes post-ingestion, and 30 minutes post-exercise on Day 1 and Day 7.
Change in LF/HF Ratio
Ratio of low-frequency to high-frequency power (dimensionless) measured using a Polar H10 heart rate sensor.
Time frame: Measured at baseline, 90 minutes post-ingestion, and 30 minutes post-exercise on Day 1 and Day 7.
Change in Total Power (TP)
Total power (ms²) measured using a Polar H10 heart rate sensor.
Time frame: Measured at baseline, 90 minutes post-ingestion, and 30 minutes post-exercise on Day 1 and Day 7.
Plan to share: No
No publications or documents are linked to this record.
Ran from Jan 2020 to primary completion in Jul 2020, 6 months.
Of 5,147 non-industry interventional studies with no phase under Motor Activity, half reached primary completion within 17 months of starting (the median), counting those still running; a quarter within 7 and three quarters within 36. This study's 6 months is below that.
Counting every sponsor, half of 5,207 studies reached it within 17 months; a quarter within 7 and three quarters within 36.
How these figures are worked out, and which studies are left out of them.
This study is completed, as verified in Aug 2026. You cannot join it, but the record below documents what was studied.
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Studies of the drug tested here: Caffeine
Birjand University of Medical Sciences