Exercise, Light & Your Body Clock

Your circadian rhythm needs a daily anchor point to stay calibrated. The most powerful anchor available to you is simple: get up at the same time every day, including weekends.

This is the single most important behavioural change in CBT-I. It works by building consistent sleep pressure (you cannot sleep in to "recover" from a bad night) and by giving your circadian rhythm a reliable signal to lock onto.

Most people with insomnia do the opposite — they sleep in on weekends, nap when tired, vary their bedtime wildly. Each of these behaviours resets the clock and perpetuates the cycle.

Within 30–60 minutes of waking, get bright light into your eyes. Outdoors is best — even on a cloudy day, outdoor light is 10–50 times brighter than indoor lighting. A 10-minute walk outside beats any indoor lamp.

If you cannot go outside, a 10,000-lux light therapy lamp used for 20–30 minutes is a well-validated alternative, particularly useful in winter or for those who work early shifts.

Morning light does three things: it stops melatonin production (waking you up properly), it sets your circadian temperature rhythm for the day, and it predicts when your body will start releasing melatonin that evening — setting up your sleep drive 14–16 hours later.

Regular physical exercise is one of the most reliably sleep-improving behaviours known. It increases slow-wave (deep) sleep, reduces time to fall asleep, and improves mood — which matters because anxiety and low mood are closely linked to insomnia.

Timing: exercise at any time of day is beneficial. However, vigorous exercise within 1–2 hours of bedtime can delay sleep onset in some people due to elevated core temperature and cortisol. Morning or afternoon is generally preferable — though if evening exercise is your only option, it is still better than no exercise.

You do not need to run marathons. A consistent 30-minute brisk walk, five days a week, produces significant improvements in sleep quality within 4–6 weeks.

Naps deplete sleep pressure. If you nap for 45 minutes at 3pm, you arrive at bedtime with less drive to sleep — making it harder to fall asleep and more likely that you will lie awake.

During the active phase of CBT-I: avoid napping entirely. This feels brutal, but it is temporary and it works — by maximising sleep pressure at bedtime, you consolidate sleep quickly.

Once your sleep is stable and efficient, a short nap (under 20 minutes, before 3pm) can be incorporated without significant disruption. But if sleep is still fragmented: no naps.