You can run a good marathon without logging 20-mile training runs.
Most running experts agree that it’s impossible to run a successful marathon without completing some long training runs first. But how long is long? American runners typically aim for 20 miles. Runners on the metric system, however, often peak at 30 kilometers, which is only 18.6 miles. And Keith and Kevin Hanson, coaches of the Hansons-Brooks Distance Project, design marathon training plans for most of the sub-elite runners they coach that regularly culminate in a mere 16-miler—and by all reports they work quite well.
In short, there is no definitive minimum distance that every runner must cover in training before running a marathon. While few runners have the talent to get away with never running more than 13 miles (the longest distance Grete Waitz ran prior to winning the 1978 New York City Marathon) in their marathon preparation, your longest run might not need to be quite as long as you think.
Why? Because, according to some experts, you can largely duplicate the benefits of doing a handful of long runs (think 16-20 miles) by doing a greater number of moderately long runs (think 10-14 miles), some of them at higher intensities. Your best results, however, might come from doing a mix of conventional long runs and long-run alternatives such as the three described below.
“During a marathon build-up, all runners, regardless of ability level, should assure themselves of being able to comfortably run at least 16 miles,” says Kevin Beck, a Boulder-based running coach and editor of Run Strong (Human Kinetics). “That said, there are a number of ways in which shorter long runs may be particularly beneficial.”