Ask A Pro: Why Does Swimming Make Me So Sleepy?

Q: After swimming in the morning I am so tired, more so than in any other sport. Why does swimming make me so sleepy?

For my entire triathlon career I have wondered why I get so tired after swimming! Growing up as a runner, I would usually feel great after a long run—my body was tired, but I was mentally alert. Once I started swimming, I could barely keep my eyes open after practice. My organic chemistry grade from the year I swam with my college swim team can attest to this fact—unfortunate scheduling placed this (already tedious) class immediately after our two-hour morning swim practice. I would race to lecture straight from the pool at 8 and, once the adrenaline of sprinting across campus wore off, it was only a matter of minutes before my eyes drooped and my head started bobbing like a chicken.

I tried everything: I brought snacks to class, figuring that as long as I was eating I could stay awake. I went to bed early (well, earlier). I tried caffeine—until then I had never liked coffee, but that year quickly progressed from gateway mochas and Frappuccinos to mainlining triple espressos. Nothing was enough to overcome the narcoleptic power of the pre-dawn 5K swim set, so the majority of my notes from that year consisted of trailed-off pen scratches and incomplete sentences. Even now, no matter how physically tired I am after running, it is never the same sleep-inducing fog as that which overcomes me post-swim practice. So what gives?

I did some research and found a few interesting theories about why swimming makes us tired. I have also added some training tips to try to mitigate the sedative effects of the morning swim workout.

Cold water: In the pool, our bodies lose heat much more quickly than in air of the same temperature due to the increased heat conduction property of water. Even when swimming hard, after a length of time in a cold pool, your core temperature will be slightly lowered. In addition, your body is expending more energy to maintain that temperature, which leads to greater fatigue than normal. After you get out and warm up, your body responds to this re-warming process as it would to drinking hot cocoa or sitting in front of the fire after a cold, winter day—by making you sleepy. So it might not be so much the coldness of the water that makes us tired as much as the re-heating process afterward. In addition, most people find swimming in water that is too warm also leads to fatigue. Try to find a training pool that maintains the water temperature somewhere around 78–80 degrees F.

There is no (healthy) way to avoid this post-swim warm-up, so if you find yourself ready for a nap, try sipping ice water instead of a hot drink after practice. Or even better, plan a short run or spin after swimming. I find if I follow swim practice with a 20-minute jog, the increased blood flow counteracts the warming up process and helps me to be more alert afterward.

Sunshine: Some people claim that the fatigue is caused by sun exposure, not the water. They have a point—after a day out skiing or even just lounging on the beach, a nap is welcomed by most. One study even claimed that subjects experienced a decrease of cognitive function after a day of sun exposure. But I would argue that a lot of us probably swim indoors a good portion of the year and are just as sleepy as our Southern-living friends. Between getting in the pool early and working indoors all day, some of us may not even see much of the sun for months at a time. If you are lucky enough to swim outdoors, be sure to wear sunscreen (duh) and try to swim later in the afternoon, or early morning when the sun is not directly overhead.

Intensity: It may seem counterintuitive, but most people tend to feel more energized after a hard workout than an easier one. After a high-intensity workout, there’s an effect that fancy scientist types call “excess post-exercise oxygen consumption” or, more commonly, after-burn. Essentially this is the extra energy your body requires to repair muscles and return your body back to resting state. If you have ever struggled to sleep the night after a hard race, despite being physically exhausted, you have experienced this feeling of after-burn. It can take anywhere from 30 minutes to 24 hours for your body to return to resting levels after an intense workout, so in this case you can use this to your advantage. Save the long endurance session for the evenings or a weekend day when you are able to head back to bed afterward. At times when you have to swim early in the morning, plan a sprint session or race-pace intervals to take advantage of the increased alertness of the post-intense workout recovery period.

Nutrition timing: Swim practices always seem to be scheduled earlier in the morning than anything else—so early that most of us don’t feel we have time to eat breakfast before diving in the pool. A swim workout after 12 hours of fasting leaves us tired, depleted and ravenous, which sets us up for a post-breakfast crash once we get out of the pool. Try to get some calories in before or during the swim if you don’t have time to eat much—even if it is just a piece of toast or glass of juice or sports drink. Include some protein afterward to balance out your carbohydrate intake, since a solely high-carb breakfast is the express train to nap time. (Michael Phelps eats a five-egg omelet along with his double stack of chocolate-chip pancakes.) The timing of caffeine intake can also have a big effect on your fatigue levels during the day. I need to have at least a small coffee when I get up, but by the time I am done with a morning swim practice, the caffeine has long worn off and I’m ready for a nap. So on the days I swim really early I try to save drinking a big coffee for afterward; then I can be productive for the rest of the morning. Exercise itself should act as enough of a stimulant—it’s not like you will fall asleep in the pool. It is when you are sitting still at a desk for hours that you are at risk of the fatigue creeping in, so that’s when to indulge in a little caffeine boost. If you are a coffee drinker, try to sip it throughout the morning instead of taking in one large dose all at once, which can create a big spike and an even bigger subsequent crash. Small amounts spread over a longer time—even if the total intake is less—will maintain more consistent levels of alertness throughout the day.

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Olympian Samantha McGlone (@samanthamcglone) is a former 70.3 world champion and was runner-up at the 2007 Ironman World Championship. She lives, trains and attends medical school in Tucson, Ariz.