The half marathon
Note
This page is a synthesis; the individual claims are graded on the pages they link to. The physiology of the half is well understood and elite training for it is well described, but the exact training balance is coaching practice rather than trial-tested.
The half marathon is the threshold event for the runners who race it fast. It is almost entirely aerobic, lasting roughly an hour for the fastest runners to well over two for many. For a runner whose finish time is near an hour it is raced right at the lactate threshold, the pace sustainable for about that long; a slower runner covers it below threshold, at an intensity they could hold for as long as they are on the course, which is why the pace label depends on the finish time (distance-specific training). For the competitive runner, that mapping sets both how the race is trained and how it is fuelled.
What decides it
Goal pace sits at the threshold, so the lactate threshold is the headline quality: the higher the pace a runner can hold without lactate accumulating faster than it clears, the faster the half. Running economy decides how far that sustainable effort carries, and durability, the resistance to the slow drift of economy and threshold over the second half, begins to matter in a way it never did over 10 km. VO₂max sets the ceiling the threshold sits beneath but is no longer the thing being raced.
Training approach
The base of high easy aerobic volume does more work here than at any shorter distance (Haugen et al. 2022), and the defining sessions are threshold and tempo runs: sustained tempos and cruise intervals at and around goal pace, which both raise the threshold and rehearse the specific effort. The long run extends the endurance the second half demands, often finished with a block at half-marathon effort to practise holding pace on tiring legs. VO₂max intervals keep the ceiling up but take a smaller share than in the 5k or 10k. The distribution is pyramidal, a large base narrowing toward a concentrated block of threshold work, the distance-specific emphasis at this end of the continuum (Casado et al. 2022).
Racing it
Start at or just below goal pace and aim for an even or slightly negative split; banking time early is almost always withdrawn with interest late (Grivas 2025). The half is the first event where fuel enters the picture. Glycogen can run low over 90 minutes or more, so in-race carbohydrate starts to help, a sound pre-race meal matters, and at the longer finishing times a degree of carbohydrate loading is worth it. See race pacing.