Background Inspiratory muscle training (IMT) has been suggested to improve respiratory function and physical performance; however, evidence in preadolescent athletes remains limited. This study examined whether adding IMT to circadian rhythm-based running programs would enhance functional and pulmonary outcomes in preadolescent male football players with at least two years of regular football training experience. Methods Seventy-five boys aged 10-12 years were categorized into morning-, intermediate-, or evening-type groups based on Morningness-Eveningness Scale for Children (MESC) scores, and each chronotype group was assigned to its corresponding running protocol with or without IMT. Over six weeks, participants completed circadian rhythm-based running sessions, and IMT groups performed graded-load IMT. Pre- and post-intervention assessments included agility, six-minute walk test (6MWT), pulmonary function (FVC, FEV1, FEV1/FVC), and respiratory muscle strength (MIP, MEP). Results Agility and 6MWT performance improved most in the morning running + IMT group compared with evening running + IMT and running-only groups (p < 0.001). FVC and FEV1 increased in both IMT groups, though gains were modest and smaller in the running-only group. Improvements in MIP and MEP did not differ significantly between groups. Conclusion Combining IMT with morning running produced the greatest improvements in agility and functional performance, while pulmonary gains were moderate and respiratory muscle strength changes were comparable across groups. IMT may provide additional benefit when integrated into chronotype-aligned morning training in preadolescent football players. Trial registration Effects of Inspiratory Muscle Training Combined with Circadian Rhythm-based Running Programs in Children Football Players, ClinicalTrials.gov: NCT06817486, Date: 27-01-2025.
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