The first important thing to note is that running a marathon is in no way easy regardless of your fitness level or previous running experience. You are running 26.2 miles - a distance that takes over 2 hours for even the worlds best athletes. Depending on your fitness/experience completing the marathon distance could take you anywhere from 2 - 10 hours.
The marathon is tough on your body and as such you need to train appropriately. According to this article the average UK marathon time is 4 hours and 37 minutes. Even standing or walking for near enough 5 hours will put a lot of stress on your body so it is vital that you train your body appropriately to withstand the demands that you are going to place upon it.
It can be done. People have done it: Could you run a marathon without training?
That said, it is a terrible idea with an abundance of risks. If your only lifetime running goal is to run a single marathon and you don't mind the potential repercussions then go for it. You almost certainly won't enjoy it and will highly likely get injured.
Many people target a marathon as a goal and build up their running, completing shorter race distances in the process. Your body will thank you for training appropriately and you will enjoy the experience and appreciate the rewards.
Most people don't regularly walk or run 20+ miles. As such one of the most important parts of marathon training is slowly building up the distance that you run. You do not want to start by running 5 miles on day 1 and then running 10 miles on day 2 - the progression is too quick and will not allow your body enough time to repair and adapt.
Adaptation is a vital part of marathon training - you want to put an appropriate amount of stress on your body such that your body can adapt and get stronger. Good marathon training is getting that balance right of appropriate stress and appropriate recovery. It is for this reason that marathon training is a somewhat long process requiring real commitment. Your body simply can not adapt and recover in a few weeks. To train appropriately it is necessary to spend at least 16 weeks (4 months) training.
Most training programs specify one 'long run' each week. The Novice 1 training program by Hal Higdon for example specifies a 6 mile long run in week 1 which increases each week up to a peak distance of 20 miles in week 15. These long runs can be classified as the endurance aspect of your training - they train your body to be able to endure running for longer and longer distances.
Looking at the program linked above you will see that the 2 other common training types are 'Easy' runs and 'Rest'. You may be thinking that 'Rest' is not training but it absolutely is, and is arguably the most important part of good training. Rest days are the days on which you allow your body time to recover, repair, and adapt. If you do not rest appropriately and continue running every day then your body will continue to break down until you have no choice about not running.
Easy runs are also extremely important in that they allow your body to get used to more running whilst not causing excessive stress to your muscles or cardiovascular system. It is important that you show restraint with your easy runs and make sure that they are actually easy. A common mistake is to run an easy run too hard simply because you feel good. Whilst you may feel good on a particular day, the effect of training is truly seen when the program is taken as a whole. You don't want to push yourself too hard on an easy run to then find that you can not complete your long run due to residual fatigue. Easy runs are as good an example as any of a situation whereby less is more.
Running a marathon requires a lot of energy. Traditionally a high carbohydrate diet has been considered optimal for running because carbohydrates provide quick easily usable fuel for your muscles.
Many runners take on fuel as they run, and many races provide nutrition on the course at 'aid stations'. Common forms of fuel include fruits - bananas and oranges, and energy gels - highly concentrated sugar gels.
It is important that you consider nutrition in your training and test any products that you intend to take on in your training. Some peoples digestive systems deal with highly concentrated carbohydrates less well than others and you don't want to find out halfway through running a marathon that the brand of energy gels that they are handing out make you feel sick.
It isn't only the type of foods that you need to consider. You also need to consider how your body deals with them whilst running. When running your body diverts attention/resources to your muscles and as such you don't want to be taking on difficult to digest foods.
Most training programs have a tapering period in the 2-3 weeks before race day. This is a period when the prescribed mileage is reduced to allow your body time to fully repair. Whilst in the midst of training a small amount of residual fatigue is acceptable but on race day you want to be 100% recovered and ready to go. Research has shown that reducing mileage does not have a detrimental effect on your fitness levels and allows your muscles glycogen (energy) stores and hormone levels to return to their optimal levels.
Having trained for months and months it may feel strange not running as much. Restrain yourself. It will be worth it.
Not your first time?
Marathons are not easy and simply finishing a marathon is an impressive feat. If you have run a marathon and 'caught the running bug' you may be wanting to run another marathon, but faster.
Once you have trained for and run a marathon your body is clearly adapted to and capable of getting you around the race distance. What you now might want to do is train your body for efficiency such that you can get around the course quicker.
To get faster you need to incorporate speed work into your training program. Some common types of speed work include:
- Interval sessions. Short repetitive runs at faster speeds to incentivise physiological adaptations (Take a look at the research). Many training programs recommend running 400 / 800 metres on a running track at a pace faster than your marathon pace followed my jogging/timed breaks. Whilst 8 x 800m with 400m jogging rest breaks is significantly less (distance wise) than a 20 mile run it will stimulate significant (albeit different) adaptations that will make you faster.
- Tempo sessions. Longer (but slower) than intervals whilst still being fast. Tempo runs are a good physical training cue but also help with the mental side of running a marathon - getting used to sustaining a high intensity activity for a longer period of time.