Here is an artice I wrote about a year ago for Florida Running and Triathlon magazine that also was posted to
www.garycohenrunning.com
that has useful info... btw, I ran 2:22 in grad school, ran 2:49 at age 49 and have done 48 marathons.
The Myth of the 20-Mile Long Run
Most marathon training programs include increasing mileage, tempo runs, mile repeats and long runs that build up to 20-milers. When it comes to long runs that prepare runners for marathons, it seems that everyone talks about “getting in their 20-milers.” Often I hear something such as, “I’m not really ready as I only got in two 20-milers.” But with all of the variables in marathon training including total mileage base, marathon experience, track speed and mental strength is the inclusion of one or many 20-milers a necessity or a myth?
The Round Number Theory
Runners love round numbers. How many times have you heard good marathoners talking about their 50-mile weeks and elite marathoners discussing their 100-mile training weeks? Just as common is the discussion of how many 20-milers were done in preparation for an upcoming marathon. Interestingly, in many foreign countries where runners use the metric system there is a similar conversation that is strikingly different. Since they don’t contest 26.2 miles, but rather 42.2 kilometers, many foreign marathoners get in long runs that are 30 kilometers – a nice round number. Is there any big difference in their 30k long runs being 1.4 miles less than a 20-miler? Probably not.
Percentage of Total Weekly Mileage
When I first started running marathons after competing as a collegiate distance runner, the conventional wisdom was that a long run should not be more than 20-25% of one’s total weekly mileage. This meant it fit into a mileage buildup phase of 80 – 100 mile weeks. Today there are many programs that include 20-milers in 50-mile training weeks which are 40% of the total weekly mileage. While a runner can complete the 20-miler, it is often necessary to taper off and recover much like for a race. It’s difficult to keep training when the long run is so draining. Additionally, when it’s marathon race day many runners are drained from too many exhausting 20-mile training runs and don’t race well.
Length of Long Run Compared to Secondary Runs
In many training plans the second longest run of the week is seven or eight miles. A 20-mile run is a major step up in distance. There are physical demands on our bodies and mental burdens on our minds. If there is a secondary moderately long run of 10 – 12 miles in the weekly plan it makes the 20-mile run less difficult as it is a smaller increase from the moderate length runs. Our bodies can much more readily accept the 20-mile distance and our brain doesn’t get as fatigued.
Dehydrating Effects of Summer Heat and Humidity
One of the toughest things about preparing for a summer or fall marathon is trying to complete long runs as temperatures and humidity percentages soar. We can hydrate before our long runs and plan the route to get water, electrolytes and calories from water fountains at parks, neighborhood convenience stores or bottles we stashed ahead of time. But we still may have trouble replenishing what we lose in sweat.
Prior Marathon Experience
If a runner has raced several marathons previously there is usually a confidence level with regard to completing the distance and how to run an appropriate pace. Experienced marathon runners may not feel the necessity to get in as many 20-milers or even one 20-miler since they know they can go the distance and how it feels. Conversely, novice marathon runners often feel that they must have some 20-milers under their belt to believe they can comfortably make it through a full marathon.
What Does This All Mean?
First, there isn’t anything magical physiologically about a 20-mile run versus a 30k run. We just can’t get enough of round numbers. Second, if our weekly mileage is 50 miles or less, we may want to cap long runs at 16 or 18 miles to avoid draining ourselves and having a negative effect on the remainder of our training plan. Third, we also may want a similar cap on long runs if our secondary runs are less than 10 miles. Lastly, we should consider doing long runs of less than 20 miles in the summer heat to decrease chances of severe dehydration. Or we can build a stronger training plan over a period of months and years. If we build up our mileage to at least 60 or 70 miles a week, add secondary runs of 10 – 12 miles and train during the fall and winter for cool weather marathons, then the 20-mile run can comfortably become a staple of our marathon preparation. There isn’t anything magical about 20-mile runs, but they can be helpful mentally and physically as we get ready for the 26.2 mile distance. I have raced fast marathons after many 20-milers beforehand and equally fast with only one or two 20-milers ahead of time. I have also raced marathons well and felt very strong with no long runs of more than 16 miles. But with secondary runs of 12 miles and dozens of prior marathons I was still confident in my ability to finish strong.
The myth of the 20-mile long run means that marathon runners in general do them because they believe they have to in order to have a successful race. Most runners don’t have confidence in their ability without knowing they did their 20-milers. So consider not doing 20-milers that are overly draining if your total mileage is low, secondary runs are short and its summertime. Work on getting your head on straight and believing in yourself. Or you can move to Europe and do 30k long runs!