Conclusion Exercise is an effective treatment for improving sleep
    in patients with insomnia. Among the various exercise interventions, yoga,
    Tai Chi and walking or jogging are more effective than other exercises.

I'm a year into daily 3-5mi fast walking (85°dp so clothes are soaked) and 6 years into chronic insomnia. I can't spot any improvement in my insomnia. I'm walking to not be sedentary so it's fine.