Abstract
This study examined the effects of cognitive fatigue on repeated sprint ability (RSA), neuromuscular performance, and vigilance in physically active young adults (N = 28, 16 males, 12 females; mean age = 20.6 ± 1.4 years). Participants were randomly assigned to a mental fatigue (MF) or control (CON) group and completed baseline and post-condition assessments following a cognitively demanding or neutral task. Repeated sprint performance significantly declined in the MF group, as shown by increased RSA mean time (Δ = 0.432 s, p < 0.001) and total time (Δ = 4.331 s, p < 0.001), with no statistically significant change observed in the CON group. Countermovement jump height remained unaffected; however, repeated jump ability showed impaired contact time (Δ = 0.084 s, p = 0.007) in the MF group. Psychomotor vigilance significantly deteriorated under mental fatigue, as evidenced by slower reaction times (Δ = 119.71 ms, p < 0.001) and increased lapses (Δ = 2.86, p < 0.001). Subjective ratings confirmed elevated perceived exertion (Δ = 0.79, p = 0.002) and mental fatigue (Δ = 8.00, p < 0.001) in the MF group, without changes in motivation. These findings may demonstrate that cognitive fatigue impairs both physical and cognitive performance, even in trained individuals.