(CNN) -- If you have a hard time crawling out of bed in the morning, it could be that your body is biologically programmed to start the day later.
Experts say a spectrum of natural sleeping and waking rhythms exists, ranging from extreme morning people to extreme "night owls."
A new study examines how morning people compare with night owls on a strength test and looks at what other physiological processes may contribute to their performance.
Researchers tested participants' leg muscle strength at various points in the day. They looked at nine "early birds" and nine "night owls," who were classified as such based on a questionnaire.
Surprisingly, morning people's strength tends to remain constant throughout the day, but night owls have peak performance in the evening, said researchers from the University of Alberta in Canada.
"We thought that morning people would be better at this in the morning, but they never changed," said study co-author Olle Lagerquist, a Ph.D. candidate in neurophysiology at the University of Alberta.
That may be because evening people show increased motor cortex and spinal cord excitability in the evening, about 9 p.m., meaning they had maximal central nervous system drive at that time, Lagerquist said.
Morning people, on the other hand, never achieve this level of central nervous system drive because the excitability of the motor cortex does not coincide with the excitability of the spinal cord. In other words, these two measures never peak at the same time, he said. Early birds' brains were most excitable at 9 a.m. and slowly decreased throughout the day.
Researchers don't know whether this means evening people who are athletes are necessarily better off.
Although night owls may maximize their strength in the evening, they are at a serious disadvantage if they have to compete in the morning. Morning people, on the other hand, would have the same average performance regardless of the time of the competition, Lagerquist said.
Based on the findings, Lagerquist recommends that people who struggle athletically in the morning try going to the gym at night, as they may feel more awake and perform better then, he said.
The study reinforces findings that athletic performance varies over the course of the day, said Dr. William Schwartz, professor of neurology at the University of Massachusetts.
Although the study is small -- 18 people participated -- it highlights problems with being a night owl that sleep experts often see in patients.
American society favors morning people, because the typical work day begins in the morning and ends in the evening, said Dr. Nancy Collop, Medical Director of the Johns Hopkins Sleep Disorders Center. Her sleep center tends to have many more night owls seeking help than early risers, she said.
Fairly commonly, people come to the sleep clinic at Johns Hopkins having been mislabeled as insomniacs when they are just night owls, Collop said.
"Their body clock is separate from what their work clock is supposed to be," Collop said.
It's very difficult for a night owl to become a morning person, Collop said.
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At least part of the reason it's so hard for a night owl to become a morning person is that morning people usually have a body clock shorter than 24 hours, while night owls usually have a body clock longer than 24 hours. Being an evening person, that was no surprise to me. If I am on vacation or between jobs and able to operate according to my body clock, I tend to go to bed and get up later and later.
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