Thousands of runners complete marathons every year. Obviously you have to have some form of physical fitness to complete a 26.2 mile run, but it really comes down to mental toughness and overcoming any psychological barriers. I hadn't run more than 3 miles before picking up "The Non-Runner's Marathon Trainer". The book was gifted to me after picking up running as a means to drop the pounds and it really helped cut the fat. Sure there was more to it, but running allows you to burn calories at an amazing rate in a shorter amount of time than many other activities.
All things being equal, the faster you run, the quicker you are done and still burn the same amount of calories for a given distance and set weight. The more you weigh, the more calories you burn. Runner's World has this great Calorie Calculator to figure out exactly what you are accomplishing as the miles pile up. Now we don't need to get to technical as it really comes down to getting off the couch and doing something. This alone gets you moving and having a goal like a marathon gives you something to reach reach for, but may seem astronomical if you have done more than a 5 miler, 5K, or even a mile run.
The Non-Runner's Marathon Trainer teaches you all aspects to consider when preparing for a marathon including a running schedule from week to week, cross training, stretching, nutrition, breathing, and most importantly proper mindset. Moving into the 7th or 8th week of training, you will definitely start to feel the nagging of your muscles and bones adjusting to your new found skill of distance running.
Key factors in the book are little mind games you can play while running and aspects you may not think of such as not listening to music while running. This may be tough for some, especially if you have an iPod attached at the hip. I have found this tip to work for me given the freedom of not dicking around with a playlist or having different songs (upbeat or slow) play on your overall mindset. Plus if you are thinking about the song, you not or at least neglect to some degree the mechanics of running efficiently.
In the end fitness is a great side effect of running, but accomplishing a goal like the marathon gives you one thing to check off your to do list for life. Most people hate running and you could have put me into that group three years ago. However, after reading this book completely prior to training, and then following its schedule week to week, you can really take it all in a little bit at a time, slowly increasing your long runs each weekend.
You will have to make the time to fit in the training, but it is well worth the improvement to your fitness. I have completed two marathons since reading the book and the second had a half hour improvement in time. I also gifted this book to two other people with one doing the marathon and the other doing a half marathon. Speed is not important for your first marathon, but I still live by "the quicker you run, the faster your done". You can pick up the Non-Runner's Trainer at Amazon or any respectable book store. It is much cheaper than the personal trainer and the pricey shoes will make up for any foregone gym fees in no time.