Mental Fatigue, Attentional Focus, and Countermovement Jump Performance

This study uses a sex-stratified, randomized, counterbalanced crossover design with repeated measures to examine the effects of acute mental fatigue and attentional-focus instructions on countermovement jump (CMJ) performance. Thirty-two physically active undergraduate students (16 women, 16 men), aged 18-30 years, will be enrolled from the Faculty of Sport Sciences at İnönü University, Malatya, Türkiye.

Each participant will complete two experimental protocols, separated by at least 72 hours: a control protocol (approximately 30 minutes of passive viewing of a narration-free nature video) and a mental-fatigue protocol (a 30-minute computerized color-word Stroop interference task). Protocol order will be randomized and stratified by sex. In both protocols, participants will perform CMJs under three attentional-focus conditions, presented in a randomized order that is held constant within each participant across sessions: no prescribed focus, internal focus (attention directed to the participant's own body movements), and external focus (attention directed to the effect of movement on the environment). CMJ height will be recorded in centimeters using a validated video-based jump-analysis application (My Jump Lab) on a tablet camera recording at 240 frames per second, with the higher of two valid trials retained as the primary outcome for each protocol-by-focus condition.

Subjective mental fatigue will be assessed immediately before and after each protocol using a 0-10 visual analogue scale to confirm the effectiveness of the fatigue manipulation. Stroop task performance (total trials, accuracy) and adherence to the assigned attentional-focus instructions will be recorded as secondary measures.

The primary analysis will use a 2 (protocol: control, mental fatigue) x 3 (focus: no prescribed, internal, external) x 2 (sex: women, men) mixed-model ANOVA on CMJ height, with protocol and focus as within-participant factors and sex as a between-participant factor. Reporting will follow CONSORT 2025 and the CONSORT extension for randomized crossover trials.

Inclusion criteria

• Age 18-30 years
• Third- or fourth-year undergraduate student in the Faculty of Sport Sciences, İnönü University
• Engaged in structured physical activity on at least 2 days per week
• Normal or corrected-to-normal vision and normal color vision
• Able to safely perform maximal vertical jumps

Exclusion criteria

• Major lower-extremity surgery or injury
• Musculoskeletal injury during the preceding 6 months that could affect jumping
• Diagnosed neurological, psychiatric, or cardiovascular disorder
• Regular use of medication that could influence alertness, fatigue, cardiovascular responses, or neuromuscular performance
• Any health condition compromising safety or measurement validity