This study aimed to examine the effects of rest periods on physiological and mechanical parameters during interval training (IT) using critical swimming velocity (CV). Ten male national-level competitive swimmers (19.5 ± 1.1 years old) swam 20 × 100 m (100IT) and 10 × 200 m (200IT) depend on critical velocity under different rest conditions. Rest periods for each IT were 10 seconds (R1) and 20 seconds (R2) per 100 m repetitive swimming distance. Heart rate (HR), rating of perceived exertion (RPE), blood lactate concentration, stroke rate, and stroke length (SL) were measured during all IT sets. HR significantly differed between R1 (164.0-173.0 beats per minute [bpm]) and R2 (151.7-165.1 bpm) throughout the 100IT but did not during the 200IT (160.1-173.5 and 157.3-167.8 bpm, respectively) (p < .05). Moreover, the mean SL during the 100IT was significantly lower in R1 than in R2 (p < .05). However, the HR and RPE increased significantly in both 100IT and 200IT irrespective of rest periods (p < .05). Therefore, all IT sets were appropriate conditions for endurance training. Rest periods may have influenced the physiological and mechanical stimulation in the 100IT at CV, suggesting that aerobic metabolism differs between conditions.
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