Found on RunnersWorld.com and written by Susan Paul
There are a number of reasons you should dial back the pace for those longer outings.
Becky asks: I’m training for my first marathon and preparing to do my first 20 mile run in a couple weeks. My training schedule for this run says “long, slow run pace.” My question is why is this run slower than others, and just how much slower do I run?
The marathon is unlike any other distance we train for in running. Typically you would train to run farther than the race distance itself; for example, when training for a 10K, you may want to do some 10-mile runs.
When marathon training, your longest runs are usually in the 20 to 23 mile range. This is because these long miles cause a great deal of wear and tear on your body. The effort needed to run 26 miles is best saved for race day.
Not all of your training runs are designated as slow, as you noted. Some of your training runs should be at or close to your goal race pace, and some of your shorter runs may be faster than your goal race pace. The distance and purpose of a training run determines the appropriate pace.
Pace depends upon the design of you training plan as well, but typically, runs in the 12 to 16 mile range are run either at goal race pace or just slightly slower than goal race pace. Runs of 10 miles or less may be done at goal race pace to even faster than goal race pace. This variety of training paces benefits you in many ways because it recruits different muscle fibers, reduces injury risk, targets different energy sources, and results in providing a broader fitness base.
In this case, it’s important to define “long.” In marathon training, runs of 18 miles or more are usually considered long runs and run at a slower pace.
As I mentioned, slowing down for long runs reduces wear and tear on your body and; therefore, shortens your recovery time so you can continue on with your training. A slower pace also trains you to be able to pick up your legs and feet for the full 26.2 miles; this feat requires an impressive combination of muscular endurance, strength, and speed.
A slower run pace also helps train your body to rely more heavily on stored fat for fuel, thereby conserving your glycogen stores. Carbohydrate and fat supply the energy necessary for muscle contractions required for movement. The body burns a blend of fat and carbohydrate for fuel all of the time. However, the faster the pace, the higher the percentage of carbohydrate (glycogen) and the lower the percentage of fat that is used. Conversely, the slower the pace, the higher the percentage of stored fat is used and the lower the percentage of carbohydrate.
Long runs also develop your mental toughness and prepare your mind for the challenges of the marathon, which is more vital than you can imagine. Distance running is hard; you will experience some level of discomfort on these long runs. Your brain will tell you to stop and you may even develop aches or pains that mysteriously disappear when the run is over. This mysterious pain is the brain’s way of trying to get you to stop. Long runs help your brain accept this discomfort and become comfortable with this “new normal.”
Weather is another factor to consider when deciding upon the pace for a long run. Training for the major fall marathons—Chicago, Marine Corps, New York—means long runs during tough summer months. When temperatures are in the 80s and humidity is 90 percent or more, doing a 20 miler is very difficult. Slowing down helps reduce the risk of heat illness.
How much you should slow down on your long runs depends primarily upon your running distance background and the weather. Runners new to distance training should plan on slowing down approximately one minute per mile or more and, if the weather is warm, plan on slowing down even more than that.
The pace should be very comfortable and conversational. Use these long runs to focus on your hydration and nutrition strategies for the marathon and covering the miles rather than the pace. Once you have completed one or two marathons, then your training can become more focused on pace and you will be able to do long runs closer to your goal race pace.