Pickleball is one of the fastest-growing sports in the United States, and people - including teenage prodigies and Hollywood celebrities - can't seem to get enough.

But how much exercise are you really getting when you play?

Researchers in Canada explored the answer to that question by measuring the physical activity intensity of singles and doubles pickleball in older adults.

The peer-reviewed study, published in the Journal of Aging and Physical Activity, suggests that pickleball can provide a moderate workout for middle-aged or older people. But they would need to play as much as 4.5 hours a week to meet recommended exercise guidelines.

If you're counting steps, the study showed you will collect relatively few during an hour of pickleball, about half as many as during an average, hour-long brisk walk.

And while the game reached a vigorous level of activity a respectable 30 percent of the time for many players, it may not provide as much physical challenge for people who are young or already in good shape.

Federal physical activity guidelines for Americans recommend at least 150 minutes of moderate intensity or 75 minutes of vigorous intensity aerobic physical activity per week for adults. Moderate-intensity exercise typically is defined as exerting yourself to the point where you can talk but not sing. Vigorous exercise, on the other hand, includes more-taxing exercises such as jogging, fast-paced cycling and singles tennis.

Pickleball, played with a paddle and perforated polymer ball, combines elements of tennis, badminton, table tennis and racquetball. Pickleball players compete in a smaller space than tennis players; up to four pickleball courts can fit on a standard tennis court. A match is played best two out of three games and each game can last 15 to 25 minutes. People of all ages play it, but the sport has long been associated with seniors and retirees after three men in Washington state invented it in 1965.

To find out if pickleball is as vigorous as jogging or tennis or closer to a more moderate activity like a brisk walk, researchers at the University of Manitoba equipped 53 recreational pickleball players with smartwatches to track their heart rates and accelerometers to measure their steps. The ages of the participants ranged from 29 to 73, though most were middle-aged or older.

They warmed up by walking or jogging around the courts for three minutes at an intensity they felt was "moderate" and then practiced hitting various pickleball shots for 2 to 5 minutes before game play. The game play lasted for at least an hour, with 22 of them playing singles, and the rest playing doubles. The time included short breaks if participants needed to rotate off a court and wait for the next available court.

The study found that based on accelerometer data showing step counts, players averaged 3,322 steps per hour, and about 80 percent of singles pickleball play was of moderate intensity. (The rest was light intensity.)

Doubles pickleball players moved less, posting only 2,790 steps per hour. During doubles play, participants spent only about half the time in moderate intensity exercise and half in light intensity.

But players' heart rate readings indicated both singles and doubles competition might be providing more of a workout than the step counts showed, said Sandra Webber, the principal investigator and lead author of the study, and an associate professor in the department of physical therapy at the University of Manitoba. Webber calls herself a "pickleball enthusiast" and at age 54 plays three to four times a week.

During singles and doubles play, many of the men's and women's heart rates reached about 111 beats per minute, a level that would put older people into the moderate-exercise range, Webber said. The mean heart rate of the participants also reached about 70 percent of maximum predicted heart rate for both singles and doubles players, which meets the definition of moderate activity, according to the Centers for Disease Control and Prevention.

Both singles and doubles pickleball players spent about 40 percent of their time in the moderate heart rate intensity zone, roughly 30 percent in light activity and about 30 percent in the vigorous zone, suggesting that with enough playing time, players could reach recommended activity goals.

"I would say that 70 percent of the time that people were on the court, they were getting exercise that would count toward their 150 minutes per week," Webber said. "Based on our results, if people play pickleball for four and a half hours a week, then they would meet their physical activity guidelines."

Michael Joyner, a professor of anesthesiology and physiology at the Mayo Clinic who was not involved in the study, said he found the heart rate responses most meaningful and would emphasize it over the accelerometer data. The study probably confirms "what your hunches would be," he said, "that you get somewhere between the upper end of moderate to the lower end of vigorous physical activity," during pickleball.

Ben Johns, 23, of Gaithersburg, Md., the world No. 1 ranked Professional Pickleball Association player for men's singles and doubles, said pickleball has more sudden movements and less downtime than tennis.

"Generally in tennis, you might be sprinting to the ball occasionally, but most of the time, you kind of know where the ball is going and you're moving at a pace that's not instantaneous," unlike in pickleball, Johns said. Also, the courts are smaller in pickleball and the sport often requires quick points near the net, he added.

But pickleball is not for everyone. As the sport grows, so do injuries. Webber said that tendon pain in elbows, widely known as "tennis elbow," is a common injury for pickleball players. She added that "there have been some very serious eye injuries with getting hit, usually with a ball but also potentially with your partner's paddle in the eye."

Webber hopes to research other potential benefits of pickleball, such as on muscle strength, flexibility and bone health.

Based on her study and personal experience, Webber remains an advocate of pickleball.

"Most people once they try it, they kind of get hooked," she said.