A three-week mindfulness intervention on mental skills, internal-load regulation, and performance in youth swimmers: a randomized controlled trial

This study examined whether a three-week mindfulness program integrated into swim training could enhance mental skills, stabilize internal-load responses, and affect short-term endurance performance in youth swimmers. Thirty trained swimmers (20 males, 10 females; aged 19.7 ± 1.7 years) were randomly assigned to an experimental group (EG, n = 15) or a control group (CG, n = 15). The EG completed 12 pre-swim mindfulness sessions, each lasting 30–45 min and incorporating breathing regulation, body awareness, and attentional-focus exercises, while the CG followed standard training only. Pre- and post-intervention assessments included 400 m freestyle time, mean velocity, and mental skills (basic, psychosomatic and cognitive). Peak heart rate (HRpeak), expressed as a percentage of theoretical maximum HR, was recorded throughout each training session, and the rate of perceived exertion (RPE) was assessed at the end of each session. The EG exhibited greater improvements in mental skills across basic, psychosomatic, and cognitive domains (all p < 0.01; cohen’s d = 2.02–2.83) compared with the CG. Despite higher HRpeak and RPE values (p < 0.001), the EG showed significantly lower intra-subject and inter-session variability, indicating a more stable internal-load profile. No significant interactions were observed for 400-m performance variables (p > 0.05). Mindfulness appears to improve athletes’ self-regulation and training consistency rather than producing immediate performance gains. Longer interventions are warranted to evaluate the long-term transfer of these benefits to competition settings.