This study tested a self-report psychological intervention in an 8-week app-based mental training program (MindSprint) using a two-arm, parallel randomized controlled trial involving 70 track athletes allocated to an intervention group (n = 35) or waitlist control (n = 35) and assessed at baseline (T0), week 4 (T1), week 8 (T2), and week 12 follow-up (T3). Five participants withdrew from the intervention group (14.3%) and three from the control group (8.6%); intention-to-treat analyses were conducted. Engagement was high (46.4 ± 7.3 of 56 sessions; 5.8 ± 1.3 sessions/week; 515.2 ± 120.4 min total practice; adherence 82.9%). Mixed-model ANOVAs showed significant group × time effects for cognitive state worry (F(3, 204) = 18.33, p < .001, ηp² = .212) and somatic arousal (F(3, 204) = 22.71, p < .001, ηp² = .250). From T0 to T2, the intervention group decreased cognitive scores from 24.8 ± 4.1 to 16.5 ± 3.5 and somatic scores from 23.5 ± 4.5 to 15.1 ± 3.9, with effects maintained at T3 (17.1 ± 3.6; 15.8 ± 4.0); controls remained essentially unchanged across timepoints. Perceived capability improved in the intervention group (105.2 ± 12.8 to 128.4 ± 10.5 at T2; F(3, 204) = 15.96, p < .001, ηp² = .190) and was sustained at follow-up (126.9 ± 11.1), while controls stayed stable (approximately 104-106). Dispositional mindfulness increased (118.6 ± 14.2 to 145.2 ± 11.8; F(3, 204) = 25.11, p < .001, ηp² = .269), and improvements in these skills correlated with reductions in cognitive (r = -.65) and somatic (r = -.61) indices and gains in perceived capability (r = .59) (all p < .001). Because objective sprint performance and physiological anxiety markers were not measured, the findings should be interpreted as evidence for changes in self-reported psychological outcomes.

• An eight-week smartphone-delivered mindfulness program (MindSprint) was evaluated in a randomized controlled trial involving 70 competitive sprinters.

•  MindSprint reduced self-reported cognitive and somatic pre-competition anxiety compared with a waitlist control group.

• Sport-specific self-efficacy improved, and the anxiety and self-efficacy benefits were maintained four weeks after the intervention ended.

• Dispositional mindfulness increased; greater mindfulness gains were associated with lower anxiety and higher self-efficacy.

• App adherence averaged 82.9%. The findings concern self-reported psychological outcomes; objective sprint performance and physiological anxiety markers were not assessed.