The day has barely started and already you're thinking a nap would be nice. You're yawning while you walk the dog, can barely focus on your computer screen and have been mainlining caffeine. Why are you always so darn tired?

When researchers measure fatigue, they're measuring how tired people are.

But they're also starting to measure something called "fatigability." That's how tired you are in relation to the activities you do.

Researchers the University of Gothenburg in Sweden explain it this way: "'Fatigue' simply refers to a state of being very tired or not being able to maintain expected force. 'Fatigability' is a measure of how fast someone gets tired."

Measuring fatigability

In most cases, when doctors or researchers try to get a handle on fatigue, it's self-reported by the patient. "Rate how tired you are on a scale of one to 10," they might ask.

And people might be tired for different reasons. One might have tossed and turned all night and just didn't sleep well, while another might have been up early to go for a run before work.

Both people might rate their fatigue the same, but it's hard to compare the results since the reasons behind them are so different.

Comparing fatigability, on the other hand, puts them on a much more even playing field. To measure fatigability, researchers ask participants to do the exact same tasks and measure how quickly they get tired.

For example, they may be asked to walk slowly on a treadmill. Jennifer Schrack, an associate professor in the department of epidemiology at the Johns Hopkins Bloomberg School of Public Health in Baltimore, has helped develop new ways to measure fatigability, according to Consumer Reports. By having participants walk on a treadmill, she can compare how tired people get from doing the same thing.

The problem with fatigue

Although you could be tired from sleepless nights, stress or just major bursts of activity, being fatigued can also be a symptom of a health issue. Fatigue can be a symptom of anemia, allergies, depression, anxiety, heart disease, fibromyalgia, rheumatoid arthritis, sleep apnea, Type 2 diabetes, hypothyroidism and many more conditions, reports WebMD.

It's normal for people to be tired every once in a while. But if your fatigue is more than just occasional, check in with your doctor to see if there's a medical reason behind it.

How to fight fatigue

man taking a walk in a city Shake off fatigue by getting out and taking a walk. (Photo: Marharyta Demydova/Shutterstock)

Whether you're tired after sitting at your desk all day or recovering from a morning workout, there are ways to give yourself a boost during the day when you're sleepy.

Here are some simple tips:

  • Get up and walk around just to get your body and mind moving.
  • Do a quick puzzle to mentally switch gears and make your mind work in a different way.
  • Listen to some upbeat music and, if no one's around, sing along.
  • Grab a healthy snack like an apple, a handful of almonds or some baby carrots.

Mary Jo DiLonardo writes about everything from health to parenting — and anything that helps explain why her dog does what he does.

What is fatigability?
Fatigability is a way to measure how fast you get tired.