The Effects of Caffeine and Vitamin C on Maximum Strength and Strength Endurance in Adolescents With Mild Mental Fatigue

Starting soon · Not applicable

Conditions studied: Maximum Force, Strength Endurance, Mental Fatigue

In brief

Objective To investigate the independent and combined effects of caffeine and vitamin C on maximal strength and strength endurance in female adolescents with mild mental fatigue. Methods A randomised, double-blind, crossover experimental design was adopted. Forty female college students presenting mild mental fatigue were recruited as participants. Each participant completed five laboratory sessions in total. The first session determined their one-repetition maximum (1RM) for bench press and back squat. The remaining four experimental sessions involved four supplement interventions administered in random order: placebo control, vitamin C (VC) alone, caffeine (CAF) alone, and combined caffeine plus vitamin C (CAF+VC). A one-week washout interval was arranged between every two supplementation trials. In each test session, participants completed a 45-min Stroop task to induce mental fatigue prior to exercise assessments. Measurements included the Visual Analogue Scale for Mental Fatigue (VAS-MF), 1RM bench press and squat performance, as well as the maximal number of repetitions at 65% 1RM for both movements. Immediately after the strength endurance test, perceived exertion and muscle pain were rated. Blood glucose and blood lactate concentrations were sampled before and after all exercise protocols. Supplementation was administered 1 hour prior to testing: a standard caffeine dosage of 3.0 mg per kg body mass and a single 500 mg dose of vitamin C were provided for the corresponding intervention groups.

Key facts

Study ID

NCT07726745

Run by

Yunliang Zhang

People needed

40

Starts

2026-07-25

Expected to finish

2026-09-22

Last updated by the study team

2026-07-27

Who can join

Age: 18 and older, up to 19. Sex: female. Healthy volunteers: not accepted.

You may qualify if…

• Aged between 18and 19years (adolescent)
• Able to complete standardized 1RM maximal strength test and muscular endurance protocol for back squat and bench press
• Meet criteria for mild mental fatigue verified by validated scale (PVT + VAS Mental Fatigue ≥4/10 or Brief Fatigue Inventory) prior to experimental session
• Habitual daily caffeine intake ≤ 150 mg/day (low-to-moderate habitual consumption)
• Non-smoker; no regular alcohol consumption
• Consistent strength training status: No physical training for the past 3 months, or maintenance of a consistent daily activity routine throughout the study
• Able to attend all scheduled testing visits, comply with pre-test restrictions (diet, sleep, exercise, supplements)
• Participant provides written assent; parent/legal guardian provides written informed consent
• Able to understand and follow verbal and written study instructions

You may not qualify if…

• History of cardiovascular disease, arrhythmia, hypertension, asthma requiring regular medication
• Known hypersensitivity or adverse reaction to caffeine, vitamin C
• Chronic neurological disorders: epilepsy, migraine disorder, ADHD with stimulant medication
• Current psychiatric diagnosis (anxiety, depression) receiving psychotropic medication
• Musculoskeletal injury in the past 3 months limiting lower/upper body maximal strength testing
• Regular intake of ergogenic supplements (creatine, beta-alanine, energy drinks) within 4 weeks before screening
• Use of any stimulants, anti-fatigue drugs, corticosteroids within 30 days prior to enrollment
• Chronic gastrointestinal disease, kidney stone history (vitamin C related risk)
• Irregular sleep-wake cycle, diagnosed sleep disorder
• Females: current pregnancy; regular oral contraceptive use
• Participated in other human intervention trials within past 8 weeks
• Investigator judges any condition that compromises participant safety or interferes with outcome measurements

Full record on ClinicalTrials.gov

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