Chemicals
Running releases all manner of wonderful chemicals into the bloodstream, including serotonin, the “happiness hormone”. But it also releases cortisol, a stress hormone that can interfere with sleep. During exercise – especially hard sessions – cortisol is released by the adrenal cortex. This has the benefit of preserving carbohydrate stores, but it also activates the hypothalamic-pituitary-adrenal axis, increasing arousal – handy for tough sessions, problematic for sleep.
What to do about it: tuck in! Don’t skimp on fuelling, especially during tough training blocks, and be sure to replenish glycogen stores before hitting the hay.
Body temperature
Sleep onset is linked with a decrease in core body temperature of about two degrees that begins about two hours prior to bedtime. Interference with this normal circadian process – for example, through doing a tough interval session – means that deep sleep suffers. Because exercise can raise body temperature by several degrees, the normal night-time drop is counteracted, leading to more difficulty falling and staying asleep.
What to do about it: use fans, air conditioners and cool compresses to decrease you core temperature.
Caffeine
Caffeine’s performance-enhancing properties are well known. But before you drink an espresso to power an evening or afternoon workout, consider the sleep-affecting consequences. Research has shown that caffeine consumption even as much as six hours prior to bedtime can cause disruptions to your slumber.
Cure: have a caffeine cut-off time, ideally at least six hours before you intend on falling asleep. So if you’re hoping to be asleep by 10pm, drink your final tea or coffee by 4pm.
Rick Pearson is the senior editor at Runner’s World UK. He’s been with the brand since 2017 and loves testing PB-friendly shoes for on and off road. Rick is a sub-three marathoner and occasionally likes to remind people of this on the Runner’s World podcast, which he co-hosts. He once raced a steam train over 14 miles (he won, narrowly) and a horse over a marathon (he lost, comfortably).
