If your music appears to slow down when you exercise, this is what could be happening in your brain

I always exercise with music, and after running for about half an hour the songs I'm listening to sound different than normal. It's the same song playing, but the tempo feels like it has slowed down.

It turns out it isn't my phone playing tricks on me — there could actually be something psychological happening to our brains when we experience this.

According to a study published in 2012 by The Royal Society, some professional sports players can experience an adjustment in their perception of time while they're active. For example, tennis or baseball players feeling the ball "slow down" before they hit it.

One explanation for this could be heightened arousal in reaction to the action, but the authors of this study say this sort of time warp is more likely to be because of the close connection between motor activity (moving the body) and temporal processing (making sense of information).

Some athletes may have evolved to be able to exploit this connection. But I'm not a professional athlete — I'm not an athlete of any sort. I don't experience this sensation of extreme concentration, allowing me to excel in sports. So what's with the music slow-down?

Many people have a musical sweet spot.

Dr Costas Karageorghis, a sports psychologist at Brunel University London and author of "Applying Music in Exercise and Sport," told Business Insider he has been studying the effects of music on exercise over the past decade. In one study, the team examined what tempo people preferred to have music at at different exercise intensities.

"It seems that as exercise intensity increases, the human organism prefers a higher tempo," Karageorghis told Business Insider. "However, there is a ceiling effect in terms of music tempo preference at around ~140 bpm and any increase in tempo beyond this does not result in correspondingly enhanced aesthetic responses or greater subjective motivation. "

The "sweet spot" for music tempo, he said, appears to be about 125-140 beats per minute (bpm). People who listen to music when they exercise, Karageorghis said, need faster, more stimulating music when working out at high intensity. This is particularly true when you're working above the anaerobic threshold — when lactic acid builds up in the body at a faster rate than it can be removed.

"For some, this need for more stimulation may translate to a perception that the music tempo is decreasing," he said.

"The phenomenon you describe is analogous to the sensation of driving on a motorway at 70 mph and listening to pop ballads. These quickly become irritating because they are incongruent with the exhilaration of high-speed driving and the heightened level of awareness demanded by the task."

Songs dont always keep up.

another possibility is that your movement rate is increasing as you work harder, but the music doesn't speed up in line with that rate. This can lead to a shift from the synchronous to the asynchronous application of music, meaning the shift of hearing music with a steady beat to music which doesn't give the illusion of the same clear pace.

"We have a natural predisposition to coordinate our movements with the rhythmic qualities of music and so when this is thwarted by an inappropriate tempo, it can cause frustration and lessen the aesthetic appreciation of the music," Karageorghis said.

The "arousal potential" of music, he explained, can strongly impact someone's aesthetic response, or how they feel about that track.

For example, his research has found that when exercising at severe intensities, people tend to dislike highly stimulative music — above 145bpm — because it is "out of kilter with the demands of the central nervous system to bring the body back towards homeostasis." In other words, our bodies don't like it because we know we have to get back to a resting state.

A specific study of whether people actually experience a slowing down of music hasn't been done, Karageorghis said, but it could be rather complex considering people generally find it tricky to differentiate between tempi of music. For example, funk often has a relatively slow tempo, but the brass instruments and rhythm give it energy.

Exercise makes us think faster.

One explanation that floated on various internet forums was that the brain may process things at a faster rate when we exercise, so external stimuli such as music may appear to decrease as a result.

Karageorghis said there is some truth to this, as during low-to-moderate intensity exercise, the brain is oxygenated and so processing speeds can be increased as a consequence, especially in older adults.

"At very high exercise intensities, the brain de-oxygenation is such that the converse holds and so there is far more limited capacity for processing of external stimuli such as music," he said.

Our brains also control our perception of time. According to Gloria Hammett, psychotherapist at Click For Therapy and Senior Partner at The Romney Centre in Southampton, how we experience time also differs greatly between different people and when we're doing different things.

"We can all relate to the experience that when we were younger, time appears to move slower than when we grow a little older," she told Business Insider. "Time is often a subjective experience and seems to almost stand still when you're intensely longing for something. For instance, people in pain often experience this slow down in time, because they're longing for relief."

In that case, experiencing the pain of intense exercise could make time feel like it's slowing down.

Karageorghis said the explanation is probably a mixture of different biological and psychological processes going on, so there's no simple answer. Whatever the reason, next time I go for a run I'll make sure I have a playlist full of songs that hit the bpm sweet spot, and see what happens.