Objectives: To evaluate the clinical effects of Zero-Time Exercise (ZTEx) for treating insomnia disorder delivered by a training course.

Hypothesis: Subjects in the ZTEx training group will have greater improvement in insomnia symptoms and daytime impairment than those in the sleep hygiene education (SHE) group at week 8.

Design and subjects: A randomized controlled trial. 32 inactive subjects with insomnia disorder recruited from the community will be randomized to ZTEx training or SHE groups in a 1: 1 ratio.

Study instrument: Insomnia Severity Index (ISI) will be used to assess insomnia symptoms and daytime impairment.

Interventions: Subjects in the ZTEx training group will attend two training lessons (2-hour each) to learn ZTEx and practice it every night for 8 weeks; subjects in the SHE group will receive sleep hygiene education with the schedule and duration that are same to the ZTEx training group.

Main outcome measures: The primary outcome measure is the ISI score. Other measures include sleep parameters by subjective sleep diary and objective actigraphy, Hospital Anxiety and Depression Scale, Multidimensional Fatigue Inventory-20 and Short Form-6 Dimension. Acceptability and compliance of ZTEx will be evaluated.

Data Analysis: Differences in the questionnaire scores, subjective and objective sleep parameters will be examined using a mixed-effects model.

Inclusion Criteria:

• Adults age 18-65 years old;
• Chinese Hong Kong residents who are able to communicate in Cantonese or Mandarin;
• A current clinical Diagnostic and Statistical Manual of Mental Disorders-fifth edition (DSM-5) diagnosis of insomnia disorder (Primary in nature) according to the Brief Insomnia Questionnaire (BIQ), a validated diagnostic tool. The criteria include having difficulties in falling asleep, difficulties in staying asleep, or early morning awakening with clinically significant consequences for daily life for at least 3 months;
• Insomnia Severity Index total score of at least 10 indicating insomnia at the clinical level;
• Willing to give informed consent and comply with the trial protocol;
• Ambulant and independent in activities of daily living;
• Physically inactive which refers to less than 150 minutes moderate-intensity activity per week or less than 75 minutes vigorous-intensity activity per week, or an equivalent combination of moderate- and vigorous- intensity activity.

Exclusion Criteria:

• Evidence of association of insomnia with medical conditions, other sleep disorders, or side-effects of medications;
• Use of medication or psychotherapeutic components for insomnia or other psychiatric disorders;
• Other possible psychiatric disorders including generalized anxiety disorder (GAD), major depressive disorder (MDD), posttraumatic stress disorder (PTSD), psychosis as screened by structural clinical interview of DSM-IV;
• cognitive impairment preventing informed consent or understanding of instructions (score < 22 in Montreal Cognitive Assessment Hong Kong version);
• Shift work;
• body mass index equal to or over 27.5, the obese criteria for Asians;
• Unsafe conditions or incapable to exercise as recommended by their physician.