| Summary: | Exercise is recommended to increase physical health and performance. However, it is unclear how low-intensity exercise (LIE) of different durations may affect or improve recovery ability. This study aimed to investigate how LIE-duration with the same volume affects recovery ability in adults. Twenty healthy male adults participated in this study. Participants were randomly assigned to the 30-min (<i>n</i> = 10) or the 1-h LIE group (<i>n</i> = 10). The intervention included sixteen exercise sessions/four weeks with a 30-min LIE group, and eight exercise sessions/four weeks with a 1-h LIE group. Heart rate (HR) corresponding to <2 mmol∙L<sup>−1</sup> blood lactate (La<sup>−</sup>) was controlled for LIE. Pre- and post-testing was conducted before and after 4-week LIE and tests included jogging/running speed (S), HR, and differences (delta; ∆) in HR and S between pre- and post-testing at 1.5, 2.0, and 4.0 mmol∙L<sup>−1</sup> La<sup>−</sup>. Only the HR at 2.0 mmol∙L<sup>−1</sup> La<sup>−</sup> of the 30-min LIE group was decreased in the post-test compared to the pre-test (<i>p</i> = 0.043). The jogging/running speed of the 1-h LIE group was improved in the post-test compared to the pre-test (<i>p</i> < 0.001, <i>p</i> = 0.006, <i>p</i> = 0.002, respectively). ∆HR at 2.0 and ∆S between the 30-min and 1-h LIE group at 1.5, 2.0, and 4.0 mmol∙L<sup>−1</sup> La<sup>−</sup> were significantly different (<i>p</i> = 0.023, <i>p</i> < 0.001, <i>p</i> = 0.002, and <i>p</i> = 0.019, respectively). Furthermore, moderate to high positive correlations between ∆HR and ∆S of all subjects at 1.5 (<i>r</i> = 0.77), 2.0 (<i>r</i> = 0.77), and 4.0 (<i>r</i> = 0.64) mmol∙L<sup>−1</sup> La<sup>−</sup> were observed. The 1-h LIE group showed improved endurance not only in the low-intensity exercise domain, but also in the beginning of the moderate to high-intensity exercise domain while the 30-min LIE group was not affected by the 4-week LIE intervention. Therefore, LIE (<2.0 mmol∙L<sup>−1</sup>) for at least 1-h, twice a week, for 4 weeks is suggested to improve recovery ability in adults.
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