This study is a single-blinded (outcome assessor) and parallel-group non-inferiority RCT. Chinese older adults aged ≥60 years with chronic primary insomnia will be randomized evenly (1:1) to either the brisk walking training group or the CBT-I group. Participants in the brisk walking training group receive an eight-week instructor-led interval brisk walking training (40 minutes/session, three sessions/week). Participants in the CBT-I group receive standard-of-care group-based eight-session CBT-I (one session/week). Self-reported and objective sleep outcomes are measured at baseline (T0), after completion of the intervention (T1), and six (T2), and 12 months after T1 (T3).

Inclusion Criteria:

1. Aged ≥60 years;

2. Ethnic Chinese; able to read, write and speak Cantonese

3. Having a Hong Kong ID;

4. Willing to wear an accelerometer on the wrist for a week to assess sleep parameters at T0, T1, and T2.

5. Score ≥10 in the Insomnia Severity Index (ISI) (presence of insomnia)

6. Experiencing any one of the following symptoms for ≥3 days per week

   1. Difficulty initiating sleep; OR
   2. Difficulty maintaining sleep; OR
   3. Early-morning awakening with inability to return to sleep

Exclusion Criteria:

1. Score ≥1 in the Chinese version of the Physical Activity Readiness Questionnaire (PAR-Q);
2. Currently regularly practicing a moderate-intensity PA program such as brisk walking or Tai Chi (≥3 times a week, ≥30 minutes/session);
3. Currently receiving or scheduled to receive CBT-I during the study period;
4. Score ≤16 in the validated telephone version of the Cantonese Mini-Mental State Examination (T-CMMSE).
5. Working nightshifts and unable/unwilling to discontinue such work pattern;
6. Having a diagnosis of a major depressive disorder, anxiety disorders or other severe mental disorder (bipolar disorders, psychosis). Those with mild depression or anxiety disorders will not be excluded;
7. Use of antidepressant or antipsychotic medication or under treatment of other serious diseases (e.g., cancer chemotherapy) known to affect sleep;
8. Presence of any serious chronic diseases which affect sleep (e.g., cancer, autoimmune diseases).
9. Having a serious somatic condition preventing the participation of brisk walking training/CBT-I.

The individual participant data contains sensitive behaviors and conditions.