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

NCT07726745 | Not Yet Recruiting DMC

• 1 other identifier: TJUS2026-30
• Study Type: interventional
• Target: 40
• Locations: 0 countries
• Sites: N/A

Brief Summary

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.

Conditions

Mental Fatigue; Maximum Force; Strength Endurance

Outcome Measures

Primary Outcomes (1)

• 1RM Squats and Bench Presses；Number of repetitions for 65% 1RM squats and bench presses

  5 week

Study Arms (4)

caf

EXPERIMENTAL

Behavioral: 1RM squats and bench presses; repetitions at 65% of 1RM for squats and bench presses

VC

EXPERIMENTAL

Behavioral: 1RM squats and bench presses; repetitions at 65% of 1RM for squats and bench presses

caf+VC

EXPERIMENTAL

Behavioral: 1RM squats and bench presses; repetitions at 65% of 1RM for squats and bench presses

Control

EXPERIMENTAL

Behavioral: 1RM squats and bench presses; repetitions at 65% of 1RM for squats and bench presses

Interventions

1RM squats and bench presses; repetitions at 65% of 1RM for squats and bench presses BEHAVIORAL

A randomized, double-blind, crossover design was employed. Professional coaches assessed the subjects' bench press and back squat performances to examine the effects of caffeine combined with vitamin C on maximum strength (1RM) and strength endurance (repetitions to failure at 65% of 1RM) during bench press and back squat training. 65% of 1RM is a widely recognized load for strength endurance testing \[28\]. The formal experiment consisted of five test sessions: one for familiarization with the entire experimental procedure and a preliminary 1RM test to reconfirm the 1RM measured three weeks prior to the study. The remaining four sessions were conducted sequentially for the control group, vitamin C (VC), caffeine (CAF), and caffeine plus vitamin C (CAF+VC) groups. Each test was spaced 7 days apart to eliminate carryover effects \[30\]. All tests were scheduled between 12:00 PM and 4:00 PM to control for the effects of circadian rhythms \[30\].

Control; VC; caf; caf+VC

Eligibility Criteria

• Age: 18 Years - 19 Years
• Sex: female
• Healthy Volunteers: No
• Age Groups: Adult (18-64)

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

Sponsors & Collaborators

• Yunliang Zhang: lead

MeSH Terms

Conditions

Mental Fatigue

Condition Hierarchy (Ancestors)

Fatigue; Signs and Symptoms; Pathological Conditions, Signs and Symptoms; Behavioral Symptoms; Behavior

Central Study Contacts

Zhizheng REN

CONTACT

+8619862079078; 19862079078@163.com

Study Design

• Study Type: interventional
• Phase: not applicable
• Allocation: RANDOMIZED
• Masking: DOUBLE
• Who Masked: PARTICIPANT, INVESTIGATOR
• Purpose: TREATMENT
• Intervention Model: SEQUENTIAL
• Sponsor Type: OTHER
• Responsible Party: SPONSOR INVESTIGATOR
• PI Title: Associate Professor

Study Record Dates

• First Submitted: July 17, 2026
• First Posted: July 24, 2026
• Study Start: July 25, 2026
• Primary Completion (Estimated): September 20, 2026
• Study Completion (Estimated): September 22, 2026
• Last Updated: July 27, 2026

Record last verified: 2026-07

Data Sharing

• IPD Sharing: Will share