June: Fuel

   A frustrating void reaches from the laboratory to your workout. Despite years of wide-ranging study, exercise physiologists can't describe the perfect running stride for speed or endurance. They haven't concocted the ideal interval workout. They don't truly know whether stretching helps or harms. They can't even tell you what to eat. Too many conflicting variables intervene, thanks to your miraculous, complicated body.

   Carbohydrate loading extends the endurance of most runners for workouts lasting 90 minutes or more by storing glycogen in the muscles, though the benefits you reap depend on how you load those carbs. Most runners begin increasing the ratio of carbs three days prior to an event even as they taper their workouts. Some simply load up the night before. And others don't give a flying bowl of pasta about what they eat-and they often win marathons, triathlons, and Olympic gold medals.

   Then there's the four-to-one rule (carbs to protein), which purportedly speeds recovery following a hard workout, but again, the science doesn't always square with reality. Here's the science: During an intense aerobic workout, your muscles are depleted of glycogen. For a two-hour window afterward, hungry muscles eagerly suck up glycogen from carbohydrates. Intuitively, you'd think this would be a good time to feast on pancakes, linguini, granola bars, and other high-carb foods. During that same workout, as your muscles stop their routine maintenance work so they can attend to the job at hand, they're depleted of the amino acids they draw from blood in order to make protein, which makes them keenly receptive to amino acids, Common sense would have you adding to your carb buffet filet of salmon, cheese, almonds, and other high-protein foods.

   Before you heap your plate high, however, recognize that your body doesn't need - and can't use - these nutrients in great quantity. An adult's muscles can absorb only about 1O to 15 grams of protein (a couple of eggs) and about 70 grams of carbs (24 ounces of cranberry juice) at a single sitting. Likewise, timing your after-workout meal matters less than the science suggests. While it's true that muscles are greedy for replenishment in the two hours after you run, it's also true that they'll take what they can get, whenever it's available. Most of us are ravenous soon after a workout, which makes for a good time to eat a robust meal. But the benefits to your performance and recovery? Feh.

   It turns out that your body is more practical and accommodating than the folks wearing the lab coats would have you believe. More to the point, general principles in biomechanics too often become weary dictates about how we train (and how we live), and produce paltry results. You are, as running philosopher George Sheehan said, an experiment of one. So experiment with your diet. But let results, not the pseudoscience in fitness magazines and Web sites, guide your decisions about what and when to eat.