Peak Performance: 7 Surprising Things That Affect Your Workout

Think twice about how random your acts of kindness are: In one part of a Harvard University study, participants were given a dollar with the option to keep it or donate it to charity, and were then asked to hold up a five-pound weight for as long as they could. Donators held the weight up for almost 10 seconds longer.

If you're an outdoor endurance runner, air pollution may make you slower. A study at Virginia Tech's College of Engineering examined seven major U.S. marathons. Researchers compared course records for the top three male and female finishing times and contrasted them with air pollutant levels. Higher levels of smog were associated with slower times, particularly in women.

You probably know that listening to a good song on the treadmill can improve your mood, make you go faster and get you in the zone. Research also shows that music can divert your mind from sensations of fatigue at low and moderate levels of intensity, meaning you can go longer without feeling tired. Crank up that iPod!

PLAYLISTS: Get the latest from SHAPE

Working out with a hangover is obviously painful. Worse, studies show that exercising while hung over could decrease aerobic performance capacity by as much as 11 percent. Drinking too much the day or night before exercising could lead to a decrease in athletic capabilities, affecting your reaction time, balance, dehydration and motor skills.

Countless studies have shown how essential Vitamin D is to your health, especially if you’re athletic. One recent study found that five minutes of UV exposure three times a week will make you faster, stronger and improve your balance and timing.

ARTICLE: The vitamin every woman needs

Did your third grade P.E. teacher have the ruthless attitude of Glee’s Sue Sylvester? She could be why you avoid the local kickball league now. A study from the University of Alberta found that a humiliating gym teacher could turn you off from athletics later in life. We say give sports another try.

Your metropolitan surroundings could put you at a fitness disadvantage. Some cities make it much easier for residents to be active and eat healthy, and SHAPE—with the American College of Sports Medicine— called them out as the fittest cities. What makes a fit city? Factors including the availability of parks, trails, farmer’s markets, healthcare providers and public transportation.

ARTICLE: How fit is your city?