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You gave it your all in your workout, and you’re feeling completely wiped out – so why can’t you sleep? When physically tired after a hard workout or race, it seems like a good night’s rest should be easy to come by, but many times, the opposite proves to be true. While moderate aerobic activity has been shown to benefit sleep, the hardest days often, frustratingly, lead to the most restless nights. Why is this the case? With sleep being such a crucial component of recovery, what can be done about it?
Why you have a hard time sleeping after hard workouts
Body temperature is one culprit behind difficulty sleeping after a hard workout. Sleep onset is linked with a decrease in core body temperature of about two degrees that begins about two hours prior to bedtime, and falls further overnight. Interference with this normal circadian process means that deep sleep suffers. Because exercise can raise body temperature by several degrees, the normal nighttime drop is counteracted, leading to more difficulty falling (and staying) asleep.
Hormones released during exercise also interfere with sleep. Cortisol, a stress hormone that plays a key role in metabolism is one of these, says exercise physiologist and nutritionist Cristina Caldwell, MS, CISSN.
“Cortisol is part of a nervous and endocrine system loop known as the hypothalamic-pituitary-adrenal axis (HPA). Among other functions, the HPA helps to regulate sleep-wake cycles,” said Caldwell. “Normally, cortisol levels are lowest in the middle of the night, build up to peak in the morning, and then gradually decrease throughout the course of the day. During exercise, though-especially hard sessions-cortisol is released by the adrenal cortex. This helps to preserve carbohydrate stores and maintain plasma glucose levels. But it also activates the HPA, increasing arousal – good for hard training, bad for sleep.”
Along with cortisol, the stress “flight-or-fight” catecholamine hormones epinephrine (or adrenaline) and norepinephrine (or noradrenaline) play a role in post-exercise sleep disruption. Plasma concentrations of these hormones, especially norepinephrine, increase markedly during exercise, particularly as intensity and duration increase, as they work to increase heart rate and blood flow to muscles, raise alertness, and mobilize glycogen and lipid stores. Post-exercise, while epinephrine levels generally return to baseline within several hours, norepinephrine levels may remain elevated for a day or two after particularly hard efforts. While increased alertness is a benefit when hitting those hard intervals, norepinephrine promotes wakefulness, making a quality deep sleep difficult when levels are elevated.
Then, there’s a relatively simple culprit of sleep difficulties after long training days: caffeine. A known ergogenic aid for endurance performance, caffeine increases alertness during your workouts, but also interferes with sleep hours later. Research has shown that caffeine consumption even as much as six hours prior to bedtime can cause disruptions, and athletes fall asleep later and sleep less when consuming caffeine during competitions. It might be tempting to drink that cup of coffee before an evening workout, especially if it’s been a long, hard day at work, but be aware of the implications at bedtime.
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How to fall (and stay) asleep after long training days
With sleep being widely considered to be one of the best restorative tools athletes have, and evidence that a single night of sleep deprivation impairs recovery from high-intensity training, what can athletes do after long, hard days?
Have a caffeine cut-off time
One simple step is to try to avoid caffeine with later workouts. Exact cutoff times can vary-the average half-life for caffeine is about five hours, but this can range from 1.5-9.5 hours.
Taking steps to cool off post-training is another way to promote post-training sleep. Fans, air conditioners, and cool compresses can all help to decrease core temperatures, and some may find bedding made of cooling materials useful. Although it seems paradoxical, a bedtime hot bath (or warming the skin, which pulls blood away from the core) also may help.
What about hormones? While cortisol and catecholamine responses are integral parts of hard training, focusing on nutrition and stress can help to modulate them. Norepinephrine and epinephrine levels are both increased in the presence of hypoglycemia. Caloric restriction and fasting increase cortisol levels. “When we restrict our calories and under nourish our body, our body perceives this as stress, which in turn causes our cortisol levels to go up,” said Caldwell. So, don’t skimp on fueling, especially during tough training blocks, and be sure to replenish glycogen stores before hitting the sheets.
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Manage life stressors
Managing stress levels in general can counteract cortisol, as well. Caldwell recommends self-care activities that decrease stress levels, such as meditation and yoga.
Practice good sleep hygiene
Finally, try to maintain good sleep hygiene habits. Turn off screens before bedtime, keep the bedroom dark, and maintain regular schedules. Try a bedtime routine, like a yoga and stretching routine for better sleep.
Supplement the right way.
While long-term supplementation with melatonin, a hormone that counteracts cortisol and rises at night to help sleep, is generally not recommended, Caldwell does encourage the use of tart cherry juice, which helps naturally increase melatonin levels, and promote quality sleep.
In an ideal world, all hard workouts would be done early in the day, and a deep sleep easily follows. But, because life rarely allows for perfection, understanding the mechanisms behind restless post-training nights can help you take the right steps to help you train – and then sleep – away, no matter what your schedule looks like.
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Jennie Hansen is a physical therapist, Ironman champion, and USAT Level 1 triathlon coach with QT2 systems. Hansen has a background as a collegiate and professional runner, as well as a number of professional triathlon podiums. She has been in the sport for over a decade.