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

NCT07726745 · Status: NOT_YET_RECRUITING · Phase: NA · Type: INTERVENTIONAL · Enrollment: 40

Last updated 2026-07-27

No results posted yet for this study

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

  • Maximum Force
  • Strength Endurance
  • Mental Fatigue

Interventions

BEHAVIORAL

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

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 \[30\].

Sponsors & Collaborators

  • Yunliang Zhang

    lead OTHER

Study Design

Allocation
RANDOMIZED
Purpose
TREATMENT
Masking
DOUBLE
Model
SEQUENTIAL

Eligibility

Min Age
18 Years
Max Age
19 Years
Sex
FEMALE
Healthy Volunteers
No

Timeline & Regulatory

Start
2026-07-25
Primary Completion
2026-09-20
Completion
2026-09-22

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Read the full study record

This page highlights key information. For complete eligibility criteria, study locations, investigator contacts, and the full protocol, visit the original record on ClinicalTrials.gov.

View NCT07726745 on ClinicalTrials.gov