You're on the starting line of what might not be your first, but certainly won't be your last, grueling marathon. You're prepped and pumped. Your body's raring to run for hours, and your brain's blissfully clueless about what's about to unfold. Let's go for an excruciatingly detailed, mile-by-mile review of your body’s outrageous marathon odyssey.

Beware the first 5 miles - enveloped by the crowd's hysteria, most runners bolt out like they're in a schoolyard sprint. According to UVA's sports medicine primary care specialist, Siobhan M. Statuta, this is a colossal mistake. You'll incinerate your energy reserves faster than a fast-food burger and enter fatigueville way ahead of schedule. In a marathon, it's the tortoise's mantra - slow and steady - that wins the race.

Unlike shorter runs that don't demand much in terms of sustenance, marathons push your body to its sweat-soaked, calorie-burning limits. According to Dr. Mark A. Harrast, a runner typically needs to down between 15 and 30 ounces of fluid every hour. And don't forget calories - munch on energy bars, gels, crackers, or pretzels, which quickly break down into glucose to fuel your body.

Stomach cramps dropping in at mile 10 to say "hi" isn't uncommon. It's estimated that as many as half of distance runners will experience the misery of gastrointestinal distress. Curbing this discomfort is tricky but experimenting with foods during your training can help identify what will wreak minimal havoc on your tummy.

As you breeze through miles 12 to 15, fatigue inevitably sets in. Your muscles, flooded with waste products (like lactic acid), start to ache and strain. But remember, luck favors the well-prepared. Training properly, alternating your stride, and remembering to eat and drink can mitigate these effects.

But now, you've come face to face with the marathon monster itself-"the wall" around miles 18 to 20. Fatigue grips you, both mentally and physically. However, ramping up on carbs and some self-encouragement can push you through.

Finally, as you cross the finish line, it's crucial to keep moving-sudden stops can cause light-headedness or even collapse due to blood pooling in your legs. So, listen to AHA and continue walking for another 5-10 minutes.

As your body cools down, don't forget to hydrate and treat those weary limbs. Be vigilant about any unusual symptoms as marathon running can potentially lead to mild kidney damage or even rhabdomyolysis, a serious condition that needs immediate medical attention. Last but not least, mind your weakened immunity; getting enough rest and maintaining good hygiene can help ward off post-race ailments.

There you have it, the harrowing journey your body undertakes during a marathon. So, lace up, load up on humor, and may the carbs be with you.