This isn't the first study to find that music tends to ease exercise: "In a typical study, from 2008, cyclists who rode in time to music used 7 percent less oxygen to pedal at the same pace as when they didn’t align themselves to the songs."
[T]here are limits to the benefits of music, and they probably kick in just when you could use the help the most. Unfortunately, science suggests that music’s impacts decline dramatically when you exercise at an intense level. A much-cited 2004 study of runners found that during hard runs at about 90 percent of their maximal oxygen uptake, a punishing pace, music was of no benefit, physiologically. The runners didn’t up their paces, no matter how fast the music’s tempo. Their heart rates stubbornly stayed the same, already quite high, whether they listened to music or not.
That result, according to a 2009 review of research by Costas Karageorghis and David-Lee Priest, researchers who have extensively studied music and exercise, is likely due to the ineluctable realities of hard work. During moderate exercise, they write, music can “narrow attention,” diverting “the mind from sensations of fatigue.” But when you increase the speed and intensity of a workout, “perceptions of fatigue override the impact of music, because attentional processes are dominated by physiological feedback.” The noise of the body drowns all other considerations.So while catchy new tunes by Ke$ha or Cee-Lo might help get you through a low- to moderate-intensity workout (e.g., a neverending mind- and leg-numbing hour on the elliptical trainer, treadmill, or on the roads), you might as well stow away your headphones when attempting a brief but brutally intense WOD or Tabata sprint session. Your Bieber Fever won't make a difference.