The long run is usually the training session that raises the most questions when preparing for a half marathon. Are 16 kilometers enough? Is it better to reach 18? Should you complete the full 21,097 kilometers before race day? The answer depends less on a concrete number than on the accumulated preparation. This session aims to improve your ability to sustain a prolonged effort and give you confidence, but it should leave you in a condition to keep training during the week.
If you’re debuting, you don’t need to complete the race distance
For a runner preparing their first half marathon with the goal of finishing, a maximum long run of 16 to 18 kilometers can be a reasonable reference. That said, those 16–18 kilometers must be the result of a progression. If your current longest outing is eight kilometers, it isn’t wise to double it from one week to the next just because the race is approaching. Muscles, tendons, and joints need to get used to spending more time running. You also must learn to regulate effort: a long run done too fast can leave more fatigue than useful training. Think of the long run as a piece of the whole. A runner who goes out three or four days a week, keeps a steady routine, and gradually increases the duration of their outings will be better prepared than another who hardly runs during the week and concentrates almost all their miles on Sunday.
Experience changes the advisable distance
If you have already run half marathons, train regularly, and are chasing a time, you can consider long runs of 18 to 22 kilometers. In some cases, slightly surpassing the competition distance helps develop endurance and to rehearse how you will manage the pace when your legs start to fatigue. The advanced-level plans from the Boston Athletic Association (organizer of the Boston Marathon, a reference for the more serious runners) include long runs close to 20 kilometers or more. However, running more kilometers only makes sense if you can assimilate them. If a 22-kilometer run leaves you several days unable to train normally, perhaps an 18 or 19-kilometer one will be more helpful. The goal isn’t to win Sunday’s training, but to arrive in the best possible condition for the race. The content of the session also matters. Most long runs can be performed at a comfortable pace, at which you are still able to hold a conversation. Runners with a solid base can introduce some segments at the planned half marathon pace, but they don’t need to turn the entire outing into a race simulation.
The effort time matters as much as the kilometers
Eighteen kilometers do not carry the same load for someone who finishes in under an hour and a half as for someone who needs more than two hours. Therefore, besides looking at distance, it is wise to pay attention to the total running time. A beginner who tries to hit a fixed number without judging their pace may end up with a session that is too long for their current level. Look at where you start from. If your usual outings last 45 minutes, the next step should not be to suddenly run two hours. Increase gradually and tailor the progression to how you feel. Elevation changes, terrain, and temperature also influence: covering 15 kilometers on a flat circuit does not necessarily entail the same effort as doing it with hills. A good long run ends with fatigue, but it should not derail the rest of your plan. If you drag fatigue for several days, experience pain that alters your running form, or repeatedly need to skip the next session, reevaluate the duration and pace. A study involving participants in half marathons and marathons found no relation between the distance of the longest run and injury risk in its sample; nonetheless, that result does not permit setting a safe distance for each person.
When to do the longest run?
As a guideline, place your longest run two to three weeks before competing. Afterwards, reduce the load to arrive rested. Trying to complete 21 kilometers the weekend before offers little additional preparation and can leave you with unnecessary fatigue. During long runs you can also test the breakfast, the shoes, and the fueling you will use in the race. If you expect to be running for a long time, practice when to drink or take carbohydrates, rather than experimenting for the first time on race day. In short, if you are debuting, don’t obsess about reaching 21 kilometers: gradually reaching around 16 to 18 can be enough. If you have experience and a higher weekly volume, you’ll be able to consider greater distances. The right long run is one from which you recover well and that fits into a steady preparation.