Whether simple lifestyle-integrated exercise training can improve insomnia remains unclear. In this study, we examined whether zero-time exercise, a simple exercise incorporated into daily routines without extra time, can improve sleep in physically inactive adults with insomnia.

This was a single-blinded, parallel-group, randomized controlled trial. A total of 140 physically inactive adults (mean [SD] age, 46.7 [14.0] years; 115 [82.1 %] women; mean [SD] insomnia duration, 4.9 [6.7] years) with insomnia disorders were randomly allocated (1:1) to the zero-time exercise intervention group or the sleep hygiene education control group. They received two 2-h zero-time exercise training sessions or sleep hygiene education lessons within 2 weeks and two phone call reminders per week for 8 weeks to follow their respective programs. The outcomes were assessed at 8, 16, and 24 weeks. The primary outcome was the Insomnia Severity Index score at week 24.

The intervention group showed a significantly greater decrease in the Insomnia Severity Index scores than those in the control group at weeks 16 (− 1.59 points, 95 % CI -3.09 to − 0.08; P = 0.039) and 24 (− 2.59 points, 95 % CI -4.17 to − 1.01; P = 0.001); however, the difference at week 8 was not significant (− 1.23 points, 95 % CI -2.54 to 0.07; P = 0.065). No serious adverse events were observed.

Zero-time exercise effectively reduces insomnia severity in physically inactive adults and can be easily incorporated into daily routines to improve insomnia symptoms and daytime impairment.