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Design: Randomized controlled study., Setting: Laboratory., Participants: 26 healthy swimmers randomly assigned to an exercise (n = 13; Ex) or control group (n = 13; Cont)., Intervention: The Ex group performed respiratory-muscle exercises for 10 min thrice a week for 4 wk., Context: Respiratory-muscle exercises are used not only in the rehabilitation of patients with respiratory disease but also in endurance training for athletes. Respiration involves the back and abdominal muscles. These muscles are 1 of the elements responsible for posture control, which is integral to injury prevention and physical performance. However, the effects of respiratory-muscle exercise on posture remain unclear., Objective: To examine the potential of respiratory-muscle exercise for improving posture., Main Outcome Measures: Spinal curvature, pulmonary function, and trunk-muscle strength were measured for both the groups at baseline and after 4 wk. The data were compared between the Ex and Cont groups with Mann-Whitney U test and preintervention and postintervention within groups with a Wilcoxon signed rank-sum test., Results and Conclusion: The spinal curvature was significantly different in the Ex group, indicating a decrease in the thoracic (-13.1%, P < .01) and lumbar (-17.7%, P < .05) angles. The Ex group presented with lower thoracic (-8.6%) and lumbar (-20.9%) angles at postexercise than the Cont group (P < .05). With respect to trunk-muscle strength, only trunk-flexion strength significantly increased from pretest to posttest in the Ex group (P < .05). For pulmonary function, forced vital capacity and forced expiratory volume in 1.0 s were significantly increased after 4 wk in the Ex group (P < .05). The results suggest that respiratory-muscle exercise straightened the spine, leading to good posture control, possibly because of contraction of abdominal muscles.