Way back when iPods were a twinkle in Steve Jobs' eye, gym rats sweated to fast-paced music, but generally couldn't tell you how many beats per minute their favorite workout tunes actually contained.
In those formative years of fitness training, a song's actual tempo was known to your instructor alone, says Alyssa Shaffer, fitness director of Fitness magazine.
"The shift has been going from instructor-based routines, to the whole iPod revolution. Now you have the ability to create your own playlist and your own intensity mixes," she says.
Instructors have always relied on the ability of a song, depending on its "beats per minute," to boost heart rates and return them to normal.
Even for the most enterprising of exercisers, though, it wasn't easy to assemble a personal workout tape with the right pulse for the right moves.
"All of a sudden, the power has shifted to the everyday person," Shaffer says.
For fitness buffs, it's now second nature to know that music in the 115 to 120 BPM range is ideal for walking, while music for cardio workouts can range from an easy 120 to a nausea-inducing 180 in a spinning class.
Anyone with a computer and an MP3 player can tailor a workout soundtrack according to the desired BPM.
With software that manipulates a song's BPM and BPM-counting gadgets on the market, staying on top of the beat becomes even easier.
There is also Exerciseradio.com, a streaming site established by New York City-based trainer Terri Walsh. The site's four channels offer music with BPM counts suitable for strength training, cardio workouts, kickboxing and boxing and yoga.
The free Internet radio station is designed to "cover the spectrum," Walsh says. "Someone who is advanced should be able to use it as well as someone who is just starting out."
Since January, Steve Boyett, known professionally as disc jockey Steveboy, has compiled music mixes with a high BPM count for a regular podcast called Podrunner. In recent weeks, Boyett's free mixes have soared to the top of the iTunes list of its 100 most popular podcasts.
Podrunner's appeal for runners and other athletes lies in its "fixed-BPM, hour-long mixes," the Los Angeles DJ says.
"The point with Podrunner is to give you a partner, an asset for your workout, that helps you literally pace yourself," Boyett wrote in an e-mail. "Not to sound like Baba Ram Dass, but the whole point is to 'be here now.' Or, more pertinently: Be. Hear. Now."
Exercisers can also fine-tune their workouts by downloading BPM-based mixes from Web sites such as fitPod. The site, "for people who work out to music," was launched in May by Baltimorean Bob Gray and Tyler Peppel, who is based in San Diego.
Boyett also creates Podrunner mixes exclusive to fitPod members. "We saw the success of Podrunner and we were pleased that it kind of validated our idea about what we wanted to do," Gray says. That is, to "make BPM-oriented music available to people involved in exercise and fitness."
Using GarageBand, Apple Computer software for creating music on a Mac, Gray has composed "Whispers of the Dharma," ambient music for yoga practitioners that is available on fitPod. To set the right tempo, Gray had to crank GarageBand "as low as it would go, which is 40 BPM."
That, as any fitness fanatic knows, is barely alive.