According to Runner's World, your longest run should occur during peak week, about a month before race day. However, the ideal distance for this run is a subject of debate. Some coaches argue that even if you can run a marathon in over 3 hours, your peak week long run shouldn't exceed that timeframe.

A 42.195 km runner on the SEA Games 31 companion race route, in My Dinh, Hanoi 2022.

To help runners determine the ideal distance, Runner's World consulted experts regarding the 3-hour rule, asking them, "How far is too far for a long run, and how far is enough?" Whether it's your first or 15th marathon, here's how to determine your peak week long run distance.

There are many ways to successfully train for a 42.195 km race, and what works for one runner may not work for another. Here's an analysis of different approaches to the longest training run, based on the philosophies of several leading coaches.

The Hansons Marathon Method limits the longest training run to 25.75 km but incorporates over 80.47 km per week, over 6 days, to build the fatigue resistance needed for race day. A 25.75 km run takes under 2 hours at a 4:30 pace and nearly 3 hours and 20 minutes at a 7:40 pace. This makes it a reasonable time commitment regardless of your speed.

Jeff Galloway's training method targets those who prefer a run/walk approach to marathons. Runners train three to four days a week, with a 42.195 km long run to build physical and mental endurance. Because walk breaks provide mid-run recovery, Galloway suggests runners can cover longer distances, even conquering the full marathon distance before race day.

Greg McMillan's training plans may require running for more than 4 hours, as they utilize run time to cater to different fitness levels. For example, McMillan suggests that your longest run should equal at least your predicted marathon time, and sometimes a bit longer.

According to McMillan: If aiming for a 3-hour marathon, run at least 3 hours, with a maximum of 3 hours and 45 minutes. For a 4-hour marathon goal, run at least 3.5 hours, with a maximum of 4.5 hours. If targeting a 5-hour or longer marathon, run at least 4 hours, with a maximum of 4.5 hours.

McMillan explains that this method addresses the physiological and psychological benefits of a long run while remaining flexible and applicable to runners of all speeds.

Runner's World training plans typically prescribe a longest run ranging from 32.19 to 35.41 km during peak week, roughly a month before the race. These plans focus on accumulated distance, not time, so the duration depends on individual pace. Runners train at least 4 days a week.

A general rule of thumb is to keep the long run distance at approximately 25% of your total weekly mileage.

While general guidelines and various training methods exist, runners can personalize their long run approach by considering their pace, experience, and goals. Listening to your body, trusting the training plan, and avoiding overtraining are crucial.

Hong Duy (adapted from Runner's World)