Effects of Mindfulness–Acceptance–Insight–Commitment (MAIC) Training on Stress and Sleep Quality in Elite Swimmers: A Randomized Controlled Mixed-Methods Trial

Elite swimmers are exposed to sustained high training loads, early-morning sessions, and restricted recovery opportunities, all of which may increase psychological strain and compromise sleep. This study examined the effects of an 8-week Mindfulness–Acceptance–Insight–Commitment (MAIC) program, embedded within routine high-load training, on athlete-specific psychological stress, subjective sleep quality, and mindfulness in elite swimmers. A randomized controlled mixed-methods design was used. Thirty elite swimmers from a provincial high-performance program in China were randomly assigned to an MAIC group or a usual-practice control group (n = 15 per group). Quantitative outcomes were assessed at baseline, post-intervention, and three-month follow-up using the Athlete Psychological Strain Questionnaire, salivary cortisol, the Pittsburgh Sleep Quality Index, and the Athlete Mindfulness Questionnaire. Semi-structured interviews were conducted with all athletes in the MAIC group after the intervention. Mixed-design ANOVAs revealed significant Group × Time interactions for athlete-specific psychological stress, salivary cortisol, sleep quality, and mindfulness. Compared with the control group, the MAIC group showed lower psychological strain and cortisol, better subjective sleep quality, and higher mindfulness at post-intervention. At follow-up, improvements in psychological stress and mindfulness remained evident relative to baseline, whereas lower salivary cortisol and more favorable self-reported sleep quality remained evident relative to the control group. Qualitative findings further showed that MAIC was experienced as feasible, low-burden, and readily integrated into the training context. Athletes described attentional resets, acceptance-based responses to discomfort, and brief post-session or pre-sleep practices as helpful for regulating cognitive reactivity and arousal. Overall, MAIC appears to be a culturally grounded and practically viable adjunct strategy for supporting psychological regulation and self-reported sleep quality in elite swimmers during demanding training periods.