Caffeine, Exercise, Physical Fitness
Conditions
Keywords
Anaerobic Performance, Upper Body, Heart Rate, Dietary Supplements
Brief summary
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.
Detailed description
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).
Interventions
DIETARY_SUPPLEMENTCaffeine
5 mg/kg of body weight of caffeine powder in a gelatin capsule, ingested daily for 7 days.
DIETARY_SUPPLEMENTPlacebo
Matching placebo capsule containing flour, ingested daily for 7 days.
Sponsors
Birjand University of Medical Sciences
Study design
Allocation
RANDOMIZED
Intervention model
PARALLEL
Primary purpose
BASIC_SCIENCE
Masking
DOUBLE (Subject, Investigator)
Eligibility
Sex/Gender
FEMALE
Age
18 Years to 30 Years
Healthy volunteers
Yes
Inclusion criteria
Active women aged 25 to 30 years Body mass index (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
Design outcomes
Primary
| Measure | Time frame | Description |
|---|---|---|
| Change in Upper-Body Peak Anaerobic Power | Measured 90 minutes post-ingestion on Day 1 and Day 7. | Peak power output (W·kg-¹) measured during a 20-second upper-body Wingate test on a cycle ergometer (Monark 891 E). |
Secondary
| Measure | Time frame | Description |
|---|---|---|
| Change in HF Power | Measured at baseline, 90 minutes post-ingestion, and 30 minutes post-exercise on Day 1 and Day 7. | High-frequency power (ms²) measured using a Polar H10 heart rate sensor. |
| Change in LF/HF Ratio | Measured at baseline, 90 minutes post-ingestion, and 30 minutes post-exercise on Day 1 and Day 7. | Ratio of low-frequency to high-frequency power (dimensionless) measured using a Polar H10 heart rate sensor. |
| Change in Total Power (TP) | Measured at baseline, 90 minutes post-ingestion, and 30 minutes post-exercise on Day 1 and Day 7. | Total power (ms²) measured using a Polar H10 heart rate sensor. |
| Change in RMSSD | Measured at baseline, 90 minutes post-ingestion, and 30 minutes post-exercise on Day 1 and Day 7. | Root mean square of successive differences (ms) measured using a Polar H10 heart rate sensor. |
| Change in SDNN | Measured at baseline, 90 minutes post-ingestion, and 30 minutes post-exercise on Day 1 and Day 7. | Standard deviation of normal-to-normal intervals (ms) measured using a Polar H10 heart rate sensor. |
| Change in LF Power | Measured at baseline, 90 minutes post-ingestion, and 30 minutes post-exercise on Day 1 and Day 7. | Low-frequency power (ms²) measured using a Polar H10 heart rate sensor. |
| Change in Cognitive Performance | Measured at baseline, 90 minutes post-ingestion, and 30 minutes post-exercise on Day 1 and Day 7. | 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. |
Countries
Iran
Contacts
PRINCIPAL_INVESTIGATORMohsen Ahmadi Mohammadnia, PhD
university of birjand
Outcome results
None listed