Sleep for endurance athletes: What the research says about naps, hunger and sleep supplements

male triathlete sleeping before training

You can nail every interval, hit your fuelling targets and your race day performance might still stall if you're not sleeping. But, for time-crunched endurance athletes juggling work, family and training, sleep is usually the first thing to go.

I've been there. I went from the back of the pack to qualifying for age-group World Championships while working full-time and raising a family. To do that, I had to do everything I could right. And sleep was always the hardest part to protect.

So I did what I did for all my training and now use for coaching age-groupers of all levels: I dug into the research. Here's what four studies say about what short sleep does to your performance and your appetite, and which sleep supplements are actually worth your money.

Short sleep costs you power, and a nap can win it back

A 2019 study from Liverpool John Moores University tested what two nights of just 3 hours' sleep does to strength and power. Fifteen trained men lifted weights at 5pm under three conditions: normal sleep, short sleep, and short sleep plus a 1-hour nap at 1pm.

After short sleep:

Grip strength dropped by 2.7%.
Bench press power fell by 11.2% and bar speed by 9.4%.
Leg press power dropped by 5.7%.
Everything felt harder, with perceived effort up across all lifts.

The nap changed the picture. After a 1-hour nap that ended 3 hours before the session, grip and bench press performance returned to roughly normal. So did tiredness, alertness and sleepiness.

This was a strength study, not an endurance one, and the sleep loss was severe. But the lesson carries over and other studies reveal an average of an 8% impact on all types of performance - speed, skill, strength, power and endurance. If a bad night is unavoidable, an early-afternoon nap that finishes a few hours before training or racing can recover much of what you've lost. Think pre-race nerves, a red-eye flight to a destination race, or a 4am transition setup. But you could also use this to get the most out of an interval session after a bad night’s sleep.

Can extra sleep make you faster? What sleep extension studies show

Most sleep research looks at what you lose when you cut sleep short. For athletes the more useful question is the reverse: what happens when you add sleep? Several studies have tested it and the answer is encouraging. Extra sleep can make you measurably faster, even if you think you already sleep enough.

The most relevant study for triathletes comes from Deakin University in Australia. Nine competitive cyclists and triathletes rode a 60-minute time trial on several days in a row under three sleep conditions:

normal sleep, about 7 hours
restricted sleep, just under 5 hours
extended sleep, about 8.5 hours, achieved simply by spending longer in bed

After three nights of extra sleep, they rode almost two minutes faster than after normal sleep (56.8 vs 58.7 minutes), roughly 3%. It didn’t feel any harder. Perceived effort was the same in every condition. Two nights of short sleep made them about 3% slower. That’s free speed, with no extra training.

Stanford researcher Cheri Mah found the same pattern in other sports. Eleven Stanford basketball players spent 5 to 7 weeks aiming for 10 hours in bed a night. Their sprint times improved from 16.2 to 15.5 seconds, and their free-throw and three-point shooting each rose by about 9%. In a smaller study of five Stanford swimmers, extra sleep brought:

15m sprints 0.51 seconds faster
Reactions off the blocks 0.15 seconds quicker
Turns 0.10 seconds faster

The athletes also reported feeling less sleepy, with better mood and more energy. These are small studies, and the swimming results were only ever presented as a conference abstract. But they all point the same way: many athletes are carrying a sleep debt they don’t know about and paying it back improves performance.

Many athletes are carrying a sleep debt they don’t know about and paying it back improves performance.

Should you bank sleep before a race?

Yes. “Sleep banking” means sleeping extra in the week before a period when you expect to lose sleep. French researchers had 12 men go to bed two hours earlier than usual for six nights, which gave them about 75 extra minutes of sleep a night. Then they stayed awake for more than 30 hours. Compared with when they had slept normally beforehand, they lasted longer on a leg muscle endurance test and found it easier.

That matters for race week. Almost nobody sleeps well the night before a 70.3 or Ironman. Nerves, an unfamiliar hotel and a 4am alarm see to that. Bank extra sleep in the 5 to 7 nights before, and one bad night matters much less. In practice:

Add 30 to 60 minutes a night, ideally by going to bed earlier rather than lying in, so your wake time stays steady for race morning.
Use your taper. Training volume drops in race week, so give some of that freed-up time to sleep rather than filling it with work or admin.
Protect the second-to-last night. It’s often your last chance at a full night’s sleep, so keep it calm and early.
Treat the night before as a bonus. If you sleep badly, don’t panic. The banked sleep has you covered.

Short sleep makes you hungrier, especially for sweets

If you've ever raided the biscuit tin after a rough night, there's a hormonal reason. A 2016 study in the journal Obesity kept 19 healthy young men in a lab for two blocks of four nights: one block with 8.5 hours in bed, the other with just 4.5 hours.

When sleep was cut short, ghrelin, the hormone that drives hunger, rose and stayed higher even after meals. Leptin, the hormone that signals fullness, didn't change.

They were given unlimited buffet meals and a snack bar. After the short nights of sleep, they ate about 340 kcal more, almost all from snacks and carbohydrates. The bigger someone's evening ghrelin spike, the more sweets they ate.

For athletes working on race weight or body composition, this matters. Poor sleep quietly undermines your fuelling plan, and it isn't a willpower problem. Protecting sleep is one of the simplest ways to keep evening snacking in check.

Do sleep supplements work? Melatonin, magnesium and glycine

Several sleep supplements have reasonably solid support, but even there timing matters more than most people think.

Melatonin. A 2024 meta-analysis in the Journal of Pineal Research found the benefit peaked at around 4 mg a day. The bigger finding for athletes was timing: taking it about 3 hours before your target bedtime worked better than taking it just before bed. Dose is a medical question, so check with your doctor or pharmacist, especially as rules on higher-dose melatonin vary by country.

Magnesium. A 2026 systematic review concluded the evidence doesn't support magnesium as a routine insomnia treatment. It's safe for most people, but if you sweat heavily or eat a restricted diet, sort out your food first. Nuts, seeds, whole grains and leafy greens are good sources.

Glycine. A 2015 study found that 3g glycine taken 60 minutes before bed helped reduce time to fall asleep and reach deep sleep. One small 2012 study found 3 g before bed reduced next-day fatigue after short sleep. With only seven participants and authors from a company that makes glycine, it's interesting but requires follow-up. Athletes could potentially take 3g glycine the day before a race, for example, when sleep tends to be short due to an early start. It may help with falling asleep as well as leaving the athlete feeling more alert after a poor night’s sleep.

Your sleep playbook as an endurance athlete

Supplements are the last 5%. These habits do the heavy lifting:

Treat sleep as part of your training plan. Schedule it like a key session, especially in heavy blocks and race week.
Get extra for heavy training and race blocks. Additional sleep can improve performance so even if you can’t always get additional shut-eye, try to get an hour or so more during clutch periods.
Keep a consistent bedtime and wake time, even at weekends. Your body clock rewards regularity.
Keep your bedroom cool and dark. Your core temperature needs to drop for you to fall asleep, and a warm shower before bed can help that happen.
Nap strategically. After a bad night, aim for up to an hour in the early afternoon, finishing at least a few hours before training or racing.
Watch the evening snacking after short nights. Plan a satisfying dinner so the ghrelin-driven cravings have less to work with.
Don't panic about the night before a race. Most athletes sleep badly then. Bank good sleep in the week leading up instead.
If you use melatonin, think about timing, and talk to a professional about the dose.

If poor sleep is persistent, talk to your GP. Ongoing insomnia deserves proper support, not just a supplement.

Frequently asked questions

How much sleep do endurance athletes need? Most adults need 7 to 9 hours, and athletes in heavy training often benefit from the upper end. In the studies above, cutting sleep to 3 to 4.5 hours clearly hurt performance and appetite control.

Should I nap before a race? If you slept badly, a nap of up to an hour in the early afternoon can help an evening session, as long as it ends a few hours beforehand. For morning races, prioritise the nights before instead.

Does extra sleep improve athletic performance? Studies suggest it does. In one study, cyclists and triathletes who slept about 8.5 hours a night for three nights rode a 60-minute time trial almost two minutes (about 3%) faster than after 7 hours. Basketball players and swimmers who extended their sleep also sprinted faster.

Is melatonin safe for athletes? Melatonin is widely used and generally well tolerated for short-term use. Timing and dose matter, so check with your doctor or pharmacist before using it regularly.

Does magnesium help you sleep? The latest review found only low-certainty, inconsistent evidence. It may help people with low magnesium intake, but it isn't a proven sleep aid.

Why do I crave sugar after a bad night's sleep? Short sleep raises ghrelin, your hunger hormone. In one study, people ate about 340 kcal more after short sleep, mostly from sweet and salty snacks.

Train smarter, recover better

Great training plans work with your life, not against it. That includes your sleep. As a coach, I build training around real data and feedback, so recovery is part of the plan rather than an afterthought.

If you're a triathlete, runner, cyclist or swimmer who wants to get more from the hours you have, book a free intro call and let's talk about your next season.