Mental Fatigue, Attentional Focus, and Countermovement Jump Performance

This study uses a sex‐stratified, randomized, counterbalanced crossover design withrepeated measures to examine the effects of acute mental fatigue and attentional‐focusinstructions on countermovement jump (CMJ) performance. Thirty‐two physically activeundergraduate students (16 women, 16 men), aged 18‐30 years, will be enrolled from theFaculty of Sport Sciences at İnönü University, Malatya, Türkiye.Each participant will complete two experimental protocols, separated by at least 72hours: a control protocol (approximately 30 minutes of passive viewing of anarration‐free nature video) and a mental‐fatigue protocol (a 30‐minute computerizedcolor‐word Stroop interference task). Protocol order will be randomized and stratified bysex. In both protocols, participants will perform CMJs under three attentional‐focusconditions, presented in a randomized order that is held constant within each participantacross sessions: no prescribed focus, internal focus (attention directed to theparticipant's own body movements), and external focus (attention directed to the effectof movement on the environment). CMJ height will be recorded in centimeters using avalidated video‐based jump‐analysis application (My Jump Lab) on a tablet camerarecording at 240 frames per second, with the higher of two valid trials retained as theprimary outcome for each protocol‐by‐focus condition.Subjective mental fatigue will be assessed immediately before and after each protocolusing a 0‐10 visual analogue scale to confirm the effectiveness of the fatiguemanipulation. Stroop task performance (total trials, accuracy) and adherence to theassigned attentional‐focus instructions will be recorded as secondary measures.The primary analysis will use a 2 (protocol: control, mental fatigue) x 3 (focus: noprescribed, 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‐participantfactor. Reporting will follow CONSORT 2025 and the CONSORT extension for randomizedcrossover trials.