The 5k
Note
This page is a synthesis; the individual claims are graded on the pages they link to. The 5k is the best-studied distance for the qualities that predict it and its energy demand is well measured, but the exact training balance is coaching consensus more than trial-tested.
The 5k is where most runners first race seriously, helped by parkrun making a measured 5 km available free every week. Energetically it is almost entirely aerobic, around 90% (Spencer & Gastin 2001; Baker et al. 2010), and for those racing it fast it is the classic VO₂max event. A runner covering it in 14 to 18 minutes is working close to their maximal aerobic effort, which can be held for only a few minutes; someone running 30 minutes or more is nearer their lactate threshold, because nobody sustains VO₂max for half an hour, so the pace label depends on the finish time (distance-specific training).
What decides it
Three aerobic qualities set the time. A high VO₂max raises the ceiling, the lactate threshold sets how much of it can be sustained, and running economy decides how fast any given oxygen cost translates into. For a well-trained runner the 5k is run at or just above the velocity at VO₂max, so the headline quality is specific endurance: holding close to that velocity for the full distance without the pace bleeding away. A finishing kick helps, but the 5k is decided far more by the aerobic engine than by the speed reserve that wins an 800 m.
Training approach
On the shared base of easy aerobic volume (Haugen et al. 2022), the defining session is VO₂max intervals: repetitions of three to five minutes at around 5k pace, which maximise time spent near maximal oxygen uptake. Threshold and tempo work lifts the sustainable ceiling so that 5k pace feels less punishing, and strides keep enough speed to finish. The funnel narrows toward 5k pace as the race approaches, the general distance-specific principle applied to this event. The training intensity distribution leans pyramidal-to-polarised: a large easy base with the hard work concentrated at and around race pace.
Racing it
Run even effort. The temptation is to go out hard on fresh legs and adrenaline; the 5k punishes it quickly, because pace held above the sustainable ceiling forces an early reliance on anaerobic energy that cannot last the distance (Abbiss & Laursen 2008). Glycogen is rarely a limiter over 5 km, so there is no in-race fuelling and little to gain from carbohydrate loading; a normal pre-race meal is enough. See race pacing.