Marathon training is not rocket science. The basic principles are pretty simple. Nevertheless, many runners—beginners and veterans alike—make fundamental mistakes in their marathon preparation. Understanding their common missteps and knowing how to avoid them will prevent you from “hitting the dreaded wall” in your next marathon. Get started with this 20-week marathon training schedule.

Failing to Run Enough

The single most common mistake runners make in their marathon training schedule is simply not running enough. There’s a reason why elite marathoners run 120 miles per week—a 26.2-mile run is an extreme test of stamina. So you need to run…a lot.

Of course, the definition of “a lot” is relative. Most runners have neither the time nor the durability to run 120 miles per week. Many busy first-timers can barely handle a third of that amount. Nevertheless, your primary objective in marathon training should be to run as much as you can without risking injury or burnout. Trust me…when you get past the 20-mile mark in a marathon, you will be thankful for every extra mile you ran in your training. (See Meb Keflezighi’s training plan.)

If durability rather than time is your major limitation, work around it with cross training. Instead of trying to run six days a week, run only four times and supplement with a couple of aerobic workouts with nonimpact activities, such as cycling or elliptical training.

The 80/10/10 Rule

Another common marathon training schedule mistake is failing to vary workout intensity sufficiently. Many runners train at the same moderate intensity day after day. However, the best results are achieved when runners follow the 80/10/10 Rule, which involves training at low, moderately-high and high intensities 80, 10 and 10 percent of the time, respectively.

Many runners avoid high-intensity running altogether. But a small amount of high-intensity running is critical. Why? Because it effectively increasing aerobic capacity and improves running efficiency. Just stick to the 10 percent mark. Anything more can be too stressful on your body and limit the amount of running you can do.

The Recovery Factor

The third most common marathon training mistake is failing to include recovery weeks during the training process. The general trend of marathon training is gradually to increase the workload. But your workload shouldn’t increase every single week. It takes 16 to 24 weeks to achieve peak fitness for a marathon. If you try to increase your training workload each week for such a long period of time, you will burn out. Instead, you should slightly reduce your workload for one week every three or four weeks to give your body a chance to fully absorb recent training and get ready for the heavier training to come. (See Boost your recovery with contrast showers.)

Basic 20-Week Marathon Training Schedule

Below is a basic 20-week marathon training schedule that avoids the common mistakes discussed above. It features more volume than a typical beginner marathon training plan, but it makes the higher workload manageable by including two non-impact cross-training workouts each week (three in the first week). The distribution of training intensities conforms to the 80/10/10 Rule, and every third or fourth week is a recovery week (indicated by gray shading).

Before starting the program, you should be able to comfortably run four miles. Below is a key for the various types of workouts included in the plan. Each workout is rated on a 1 to 10 scale of perceived effort

• Cross Training – Choose a non-impact aerobic activity such as swimming, cycling, or elliptical training. Do these workouts at an “easy” intensity that corresponds to a rating of 4.
• Foundation Run – Run at a steady, easy intensity that corresponds to a rating of 4.
• Fast-Finish Run – Run the first component at a perceived effort rating of 4, then run the moderately-hard portion at an effort level of 6 or 7.
• Fartlek Run – A fartlek run is a mostly easy run with a handful of short, hard efforts sprinkled throughout. Run the “easy” segments at a perceived effort level of 4, then raise your effort level to 8 or 9 for the “hard” portions. You can run hard whenever you like; just allow enough time between hard intervals to fully recover.
• Long Run – A long run is simply a long foundation run. Start at an effort level of 4 and increase your perceived effort level slowly as these runs drag on, even though your pace is consistent.
• Hill Repetitions Run – Do the first and last parts of these runs (warm-up and cool-down) on relatively flat terrain. Perform the hill repetitions on a moderately steep hill at an effort level of 8. Go as slowly as necessary to recover during the easy segments between hill reps.
• Tempo Run – Do the easy first and last parts of these runs at an effort level of 4. Do the middle part at a moderately high intensity of 6 to 7.
• Interval Run – Warm up and cool down at an easy effort level of 4. Run the “hard” intervals at an effort of 8. Go as slowly as necessary to recover during the easy segments between intervals. (Learn more about the benefits of interval training.)