Half marathons and marathons can be over in a matter of hours, but runners, both newbies and elite, often spend months training for the 13.1- and 26.2-mile races. Robert Chapman, director of the Human Performance Laboratory in Indiana University's School of Health, Physical Education and Recreation, and coach of Brook Team Indiana Elite, discusses four common mistakes runners make when preparing for these major races.

Mistake #1: Discounting the importance of the weekly long run.

For the half-marathon and marathon, the weekly long run is one of the most important components of training. The adaptations that take place physiologically and psychologically during the long run are critical in helping the runner complete the race distance, as well as helping the runner achieve a goal time. Key adaptations that take place with the weekly long run:

• Increased storage of muscle glycogen. Glycogen is the primary storage form of carbohydrates in the body, and the amount of glycogen the body can store is limited. In a typical person, there is enough glycogen present to fuel about two to three hours of moderate exercise. When glycogen stores get low or run out, the runner "hits the wall" and will struggle to finish the event. However, glycogen stores can increase as a result of training, and stores improve significantly as a result of including long runs each week.
• Improved psychological ability to handle the race distance. With each weekly long run, there is an improvement in the runner's ability to mentally tolerate exercising for long periods of time.
• Improved ability to absorb and tolerate the "pounding" the legs will take during the race. Feet, joints, tendons and muscles are all gradually strengthened over time from the overloading they receive from the weekly long run. Many runners who fail to finish a marathon do so because of leg pain and discomfort, resulting from the weight-bearing pounding over 26 miles.
• Chapman recommends a long run once each week, starting early in training at about 20 percent of overall weekly volume. From there, athletes in the half-marathon should aim for a minimum long run distance of 8-10 miles, ideally completed at least twice before their race. Marathoners should aim for a minimum long run distance of 15 miles, completed at least twice before the race, with at least two long runs of around 20 miles being ideal.

Mistake #2: Selecting a race without considering the weather or lifestyle considerations for training.

Most marathons are held in the spring or fall because of the milder temperatures in the Northern Hemisphere. Most experts recommend a training buildup of 10-16 weeks for most experienced runners prior to a marathon, perhaps a few weeks less for a half marathon.

For athletes who select a spring race, this will mean completing a large portion of their training during the thick of winter — where cold temperatures, snow and ice, and limited daylight hours can all have a dramatic effect on the quality of training and motivation for completion. Runners with work and family commitments, who have to train in early morning or evening hours, may find preparation for a spring marathon challenging. For athletes who select a fall marathon or half marathon, the bulk of the training load will come during the heat and humidity of summer. For most runners, training in extreme heat is more challenging than training in cold weather, where additional clothing can be worn. While it may be considerably easier to get runs in during early morning or late evening hours, summer is typically full of family vacations and weekend outings that can make sticking with a rigid training routine more difficult.

In the end, when deciding on a marathon or half marathon, each runner should take a look not just at the time of the year of the race, but the logistics of how well they will be able to complete their training in the three to four months prior to the event.

Mistake #3: Failing to "practice" the race day routine.

After weeks and weeks of training, many runners end up failing to finish or meet their goals — often due to some simple, small detail that was overlooked regarding race day routine. Here are some examples:

• Not being used to running in the early morning, when most races start.
• Logistics such as bus departure for the race start, parking, proximity of race to hotel.
• Breakfast decisions, such as what and when to eat.
• Clothing, shoes, socks — will they cause chafing or blistering?
• Uncertainty about the sports drink provided by the race and whether it upsets runners' stomaches.
• Shoe choice — newer or older pair.

Many of these questions can be worked out during weekly long runs, such as clothing and breakfast choices. Runners also can contact race organizers for details about sports drinks and then try out the drinks during training. The weekly long run is not just an important component for training adaptations. It is also a great "dry run" for the race.

Mistake #4: Starting the race too fast.

Three athletes who Chapman coaches qualified for the U.S. Olympic Marathon Trials and another won the Columbus Marathon in her debut at the distance. In all four cases, the athletes executed a "negative split" strategy — where the second half of the race was faster than the first.

Based on the paces completed in training, runners should have a strong idea of what pace they are capable of executing for the race distance, with slight modifications based on changing race day conditions such as weather. Once that pace is determined, Chapman recommends a conservative approach, especially if the goal is simply to finish the race. Even if a runner has a goal time in mind, a conservative, negative split approach will often lead to best performances, typically without the late race discomfort that normally accompanies a more aggressive pacing approach.

Starting out at a conservative pace can often be a challenge with the excitement of the race start, the bands and music, and even fireworks that are present when the gun fires. However, the most common recipe for disaster in a marathon is going out too fast.