It might sound hippy-dippy, but repeating a meaningful phrase or mantra can help you power through a difficult workout. Though yogis chant the traditional "Om," you can use any word that summons strength. One of McGee's students repeats, "Stay strong all day long" when she starts to lose motivation. It reminds her that finishing the workout will make her feel stronger for the rest of the day.

According to sports psychologists, mantras should be action-based, short, instructive and positive. Choose a mantra that describes what you want to feel, rather than one that acknowledges pain. "Define yourself" was the mantra chosen by Deena Kastor in 2005 when she became the first American to win a major marathon since 1994. Sarah Reinertsen chose "You're tougher than the rest" to qualify for a spot at the Ironman World Championship, where she became the first female leg amputee to finish the race.