Why Run so Far?
As I have had the opportunity to train, treat the injuries for and generally have discussions with runners of all ages, levels of competition and skill, I have found a common belief. The assumption seems to be that the farther you run, the better off you will be. This is mostly true of runners who race anywhere between 1 mile and 5 miles. There seems to be a philosophy that running long, slow training runs of 12-15 miles will help them compete better in a race of significantly shorter distance. One of the problems this philosophy creates is that it requires extended training runs and an accumulation of weekly mileage that can top 60 miles per week. If averaged out over the course of five days, it would equate to running 12 miles per day. Some even strive for 100 mile weeks. The most common explanation I get is that the purpose of this volume of miles is to “build a base.” The base to which they are referring is the aerobic base, or the level of aerobic fitness the runner has. However, what is often missed is that long, slow training runs do not have the same physiological demands on the body as 3-5 miles of fast running.
A question to consider is whether a runner would likely do well in a 3-5 race running at the same pace in which they run their 12-15 mile long runs. Most would immediately acknowledge that they would finish quite poorly. Nonetheless, this is one of the most common components in the training programs of such runners.
Let’s take a look at a couple very important physiological principles as they relate to this topic. First, racing 3-5 miles requires the ability to perform at a high heart rate for a relatively prolonged period. This requires the ability of the body to process oxygen at a very high rate. The ability to process a given amount of oxygen per minute per unit of body weight is called the VO2 max. It also requires the ability of the body to avoid the effects of lactic acid accumulation and continue to perform at a high level. Both of these issues are best trained with gradually increasing durations of high intensity bouts of exercise (running). Basically, run fast, rest, run fast again. Gradually increase the amount of time spent running fast and decreasing the time resting. Eventually, the runner will be able to run faster for the entire distance.
The other factor is the way the body gets energy during running different distances and different speeds. The body has three different methods of delivering energy to muscles for production of contractions. The first is the immediate system called the ATP-PCr system which supplies energy for the first 15 -30 seconds of activity regardless of intensity. The second system to kick in is the glycolytic system which is split into aerobic and anaerobic components. The difference between aerobic and anaerobic is whether lactic acid is produced at the end of the process. Generally, lactic acid is produced with high intensity exercise. Slow exercise (low intensity) follows the aerobic process and does not produce lactic acid. It is this difference that makes higher intensity interval training preferable to long, slow distance training. With higher intensity interval training, the body is trained to handle the onset of blood lactate (OBLA). The requirement is not present with long, slow distance training. Once lactic acid builds up, it can significantly limit the ability of muscles to maintain a high level of performance. The last system to take over is the oxidative system. It uses oxygen to fuel chemical reactions to produce the needed energy for continued performance. It kicks in once the glycolytic system is depleted.
In the most general terms, the body responds to specific demands. If it is trained to go fast and far, it will adapt to go faster and farther. If it is trained to go slowly and farther, it will adapt to go farther, but at the slower speed. Which would you prefer if your goal is to win a race or to set a personal record for a race?
Fitness
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