With the Fall marathon season in full swing, thousands of runners are gearing up for the big day.  Just as important as their broken-in shoes and heart rate monitor is their source of motivation, inspiration and distraction: their tunes.

Running with music has become so common that the two biggest names in both industries, Nike and Apple, have been joined at the hip with the Nike + iPod combination. So, what is it about music and running, or any exercise, that feels so right?

Several recent studies try to chase down the connection between our ears and our feet.

For the last 20 years, Costas Karageorghis, a sports psychologist at Britain’s Brunel University, has been setting the research pace for understanding our need to groove and move.

In addition to his lab research, Karageorghis has helped create a half marathon in London that tries to find the perfect music mix of live bands based on his research of human reaction to rhythm. The second annual "Run to the Beat" event was held a few weeks ago with 9,000 laboratory rats, er, runners either enjoying the live music or listening to their own mix of tunes on their MP3.  Karageorghis even offered a scientific selection of songs based on his findings.

According to Kargeorghis, there are four factors that contribute to a song's motivational qualities: rhythm response, musicality, cultural impact and association.

The first two are known as "internal" factors as they relate to the music's structure while the second two are "external" factors that reflect how we interpret the music. Rhythm response is tied to the beats per minute (bpm) of the song and how well it matches either the cadence or the heartbeat of the runner. A song's structure such as its melody and harmony contribute to its musicality. The external factors consider our musical background and the preferences we have for a certain genre of music and what we have learned to associate with certain songs and artists.

Picking the right music can have several benefits.

Syncing beats per minute with an exercise pace increases your efficiency. In a recent study, subjects who cycled in time to music found that they required 7 percent less oxygen to do the same work when compared to music playing in the background. Music can also help block out the little voice in your brain telling you its time to quit. Research shows that this dissociation effect results in a 10 percent reduction in perceived effort during treadmill running at a moderate intensity.

In the current study, published in the Journal of Sport and Exercise Psychology, 30 subjects synchronised their pace to the tempo of the music which was 125 bpm. Before the experiment, a pool of music was rated using a questionnaire tool (the Brunel Music Rating Inventory) which then selected the most motivational pieces for the treadmill test. The subjects were given a choice of either pop or rock music.

When compared to a no-music control, the motivational synchronised music led to a 15 percent improvement in endurance.

"The synchronous application of music resulted in much higher endurance while the motivational qualities of the music impacted significantly on the interpretation of fatigue symptoms right up to the point of voluntary exhaustion," Karageorghis reported.

Matching the beats per minute of our music with our exercise heart rate also takes an interesting non-linear path, according to research.

Karageorghis found that when our hearts are performing at between 30 and 70 percent of maximum, we prefer a somewhat linear increase from 90 to 120 bpm. However, when we reach our anaerobic threshold between 70 and 80 percent of maximum, we prefer a jump in rhythm from 120 to 150 bpm. Above 80 percent of maximum heart rate, a plateau is reached where even faster music is not preferred.

Another new study by researchers from Liverpool John Moores University, and detailed online in the Scandinavian Journal of Medicine & Science in Sports, looked at the tempo angle differently. Instead of a mix of different songs at different tempos, they asked a group of cyclists to pedal to the same song over three different trials.

What the subjects did not know is that the researchers first played the song at normal speed, but then increased or decreased the speed of the same song by 10 percent. The small change was not enough to be noticed, but it did have an effect on performance.

Speeding up the music program increased distance covered/unit time, power and pedal cadence by 2.1 percent, 3.5 percent and 0.7 percent, respectively. Slowing the program produced falls of 3.8 percent, 9.8 percent and 5.9 percent. The researchers concluded that we increase or decrease our work effort and pace to match the tempo of our music.

Finding the right beat has now become even easier with a couple of cool software plug-in tools, Cadence or Tangerine.  Cadence is an iPhone/iPod Touch app, while Tangerine is Mac only. By integrating with your iTunes library, they can build a custom playlist based on the BPM range you provide, while arranging the songs in several different tempo shapes including warm-ups and warm-downs. With the right mix, your brain and feet will be in perfect harmony.