Training · Running
The long run: what it is actually for
Nearly every running plan ever written has one run a week that is longer than the rest. It is not there for the distance itself, and understanding what it is doing explains most of the rules that surround it — why it is run slowly, why it grows gradually, and why the useful unit is time rather than kilometres.
The long run is the session where duration is the stimulus. Extended time at low intensity is the principal way endurance is built, and there is no way to compress that into a shorter, harder session — a hard forty minutes and an easy two hours are not interchangeable, because they are asking different systems to change.
It also does something no other session does: it accustoms the body to being on its feet for a long time. Anybody preparing for an event lasting hours has to have spent hours running beforehand, and the long run is where that happens.
Asking how long a long run should be in kilometres has no general answer, because the same distance is a routine outing for one runner and the longest thing they have ever done for another. The question that does have an answer is what proportion of the week it should be, and the conventional guidance is that it should be a substantial but not dominant share of total weekly volume.
The failure mode this guards against is a common and specific one: a runner covering very little during the week and then doing a very long run at the weekend. The week does not support the long run, so the long run becomes the only real training and also the injury risk, and the imbalance tends to grow rather than resolve.
The conventions that follow from this:
- Measure in time, not distance — Ninety minutes is ninety minutes whether it is flat or hilly. Fifteen kilometres is a very different session on those two courses.
- Grow it gradually — The tissue adaptation is the slow one. Jumping the long run substantially in a week is the classic route to an overuse injury.
- Cut it back periodically — Most plans reduce the long run every few weeks rather than increasing it monotonically, because fatigue accumulates faster than fitness.
- Run it easy — The duration is the stimulus. Running it hard changes the session into something else and costs days of recovery.
Long runs introduce logistics that shorter runs do not have. Water becomes a consideration in warm weather, and so does what to do with a key and a phone. Chafing, which is invisible at forty minutes, appears reliably at two hours and in places that are specific to each person.
Fuelling matters past about ninety minutes, and this is the one place where practising in advance is genuinely necessary — an unfamiliar gel taken for the first time during an event is a well-known way to have a bad day. What to take is individual and is not something a page can decide for you; that it should be tried in training first is not.
Questions this guide answers
Listed so you can tell at a glance whether this is the page you wanted. HobbyHQ keeps one guide per question family rather than a page per phrasing.
- what is the point of the long run
- how long should my long run be
- how fast should I run my long run
- why is the long run important
- should I increase my long run every week
- is the long run measured in time or distance
Part of Running. Last reviewed 2026-08-30.