A runner in the Marine Corps Marathon listens to headphones during the race in Washington D.C., last Sunday. Music may help pass the time, but if you’re running competitively, it’s now banned by USA Track & Field, the national association for runners. A new rule this year, bans the use of headphones and listening devices at its official races for the safety of the competitors and to prevent runners from gaining a competitive edge.

New York Times / Stephanie Kuykendal

Liz Wimmer pumps up the volume on Mary J. Blige, Beyonci and 50 Cent to get moving.

The 31-year-old Denver paralegal has lost more than 80 pounds the past two years by setting her workouts to a playlist that strategically mixes slower and faster-paced music. Her strategy: Run one song, sprint two.

“Hip-hop and rap have a steady beat and that helps me to run fast,” Wimmer said. “Music makes working out more fun; it’s easier to get it done. Whenever I hear a song that I like on the radio I go and download it.”

From techno to country to heavy metal, what type of music gets your blood flowing is an extremely personal choice. But with iPods and other digital music players as ubiquitous at gyms these days as water bottles and free weights, several artists are mentioned over and over again by trainers and plugged-in athletes as major motivators.

Who tops the list? Beyonci, Justin Timberlake, the Black Eyed Peas, Avril Lavigne, 50 Cent, Fall Out Boy, Maroon 5 and Green Day were all named as favorites by trainers at the Denver Athletic Club.

“Music is addictive,” said Anna Sablik, a personal trainer and endurance coach at the club. “It can make a workout go by so much faster and help you overcome a mood. If you’re feeling groggy, just hit a fast song and you automatically feel so much better.”

In Sablik’s spinning classes, she plays a wide variety of music, including the theme song to “Rocky” and Van Halen and Coldplay.

“I like to use more upbeat songs to set a fast-paced tempo,” said the trainer, who prefers to run to country band Rascal Flatts. “But it’s tough because everyone has such different tastes. What gets me going might drive someone else crazy.”

According to a recent survey on Fitness magazine’s website, readers ranked Justin Timberlake’s “SexyBack” as their No. 1 workout song, followed by Christina Aguilera’s “Ain’t No Other Man” and Fergie’s “Fergalicious.” “Girlfriend,” by Avril Lavigne, and “Maneater,” by Nelly Furtado, also made the top five.

So what’s in your MP3 player?

Denver student Andrew Karasek said his iPod Nano is loaded with the Strokes and Rage Against the Machine.

“They get me fired up,” he said.

Trainer Ian Abeyto said he prefers to do cardio to classical music, including Beethoven’s Ninth Symphony and Vivaldi’s “The Four Seasons.”

“It’s amazing,” he said. “Classical music can really get you in the zone.”

And if you want more than tunes to help guide your workout, several websites — including cardiocoach.com and itrain.com — offer the ability to download audio instructions by professional trainers onto your MP3 player for a fee.

Podfitness.com lets users create customized workouts with celebrity trainers, including aerobics guru Kathy Smith, professional bodybuilder Jay Cutler and former child star and certified trainer Danny Bonaduce. It also allows you to set the instructions to music from your personal library.

“If you want to do yoga to heavy metal, that’s totally up to you,” said executive vice president Alan Winters. “The music is one of the novel parts of our business. What’s more motivating than working out to something you already picked, that you already love?”

For a monthly fee of $19.95, Podfitness.com customers can download two personalized workouts per day. The website currently has nearly 25,000 members.

Jennifer Lesea-Ames, a personal trainer at an athletic club in Denver, launched Fitwisetraining.com in June, which sells downloadable video workouts by professional trainers. Prices range from $1.99 per exercise to $9.99 for an entire fitness program.

“I think a lot of people are visual learners, so we’re focusing on video,” she said. “One main reason people hire personal trainers is so they can see a trainer demonstrate the moves.”

Lesea-Ames said her music library varies from Tom Petty to AC/DC. “If I’m tired, it’s definitely techno — something more fast-paced and upbeat,” she said. “But if I’m feeling good and just want a chill workout, it’s more classic rock.”