When the first marathon runner, the Greek soldier Pheidippides, finished his historic dash from Marathon to Athens in 490 BC, he likely hadn't sipped a cup of coffee beforehand. But if he had, he might have improved his time, or at least felt better along the way. Medical research has shown that caffeine may improve aerobic endurance performance in a couple of ways. First, it stimulates the central nervous system, which makes athletes feel more energetic, both physically and mentally. It also stimulates the release of adrenalin, which enhances cardio function and fuel utilization. When runners' reserves slump, caffeine helps mobilize free fatty acids for energy use. But caffeine can help in the endurance sport of life, too. Who among us wouldn't appreciate a few spare fatty acids transforming into flights of spunk? Maybe if the noble Pheidippides had enjoyed some caffeine-enhanced gels from a sponsored rest stop, his post-race mood would have been higher. Instead, he simply uttered "Niki!" (not, as it turns out, the name of a doting spectator, but, rather, the Greek word "Victory!") Then, he died.

Caffeine content comparisons (in milligrams)

double espresso (2 oz) 128

drip coffee, coffeehouse strength (12 oz) 215

cola (12 oz) 35

Mountain Dew (12 oz) 54

black tea (12 oz) 75

green tea (12 oz) 52

Hershey's chocolate bar (1.55 oz) 9

Haagen-Dazs Coffee Ice Cream (1/2 cup) 30

Gu Energy gel packet (most flavors) 20

Fit Supa Goo packet 35

Extra Strength Excedrin (2 tablets) 130

sources: Harvard Health Publications, Harvard Medical School; Mayo Clinic; Georgia State University (sic.); University of Guelph, Canada (sic.)