Half Marathon Training: Mileage, Long Runs, and Recovery Days

Half marathon performance is decided mostly by three variables: how much easy running you accumulate each week, how long your long run goes, and how disciplined your recovery days are. Session variety matters far less. Build weekly volume in steps of roughly 10 percent, cap the long run near 30 percent of weekly volume, and run recovery days slowly enough to speak in full sentences.

Why mileage carries the half marathon

The half marathon sits close to the intensity you can sustain for about an hour to ninety minutes, which means aerobic durability rather than top-end speed determines the outcome. A runner with a fast 5K and 35 km per week will usually lose to a runner with a slower 5K and 70 km per week over 21.1 km, because the second runner's pace decays less over the final third.

Weekly volume builds the peripheral adaptations that make a given pace cheaper: capillary density, mitochondrial content, fat oxidation, and the connective-tissue tolerance that lets you keep running when form starts to degrade. Those adaptations respond to repeated, moderate stress over weeks. There is no session that substitutes for them.

Gabbett (2016) makes the related point about risk: injuries follow rapid load increases and inappropriate programming rather than high load itself, and athletes accustomed to high chronic loads tend to sustain fewer injuries than those training at lower workloads. The goal is high volume arrived at slowly.

Volume targets by goal

Two caveats. These are ranges for a 12 to 16 week build, not starting points. If you currently run 30 km per week, a 12-week build reaching 55 km is reasonable; reaching 80 km is not. And the top of each range assumes you are sleeping adequately and eating enough, because volume without recovery capacity is just accumulated fatigue.

How to raise mileage without a setback

Nielsen and colleagues (2014) provided the clearest recreational-runner data on this. Across 874 novice runners followed for a year with GPS watches, 202 sustained a running-related injury. Runners who increased weekly distance by more than 30 percent over a two-week period had a higher rate of distance-related injuries, including patellofemoral pain, iliotibial band syndrome, medial tibial stress syndrome, gluteus medius injury, greater trochanteric bursitis, tensor fascia latae injury, and patellar tendinopathy, than runners progressing less than 10 percent. Notably, plantar fasciitis, Achilles tendinopathy, and stress fractures did not track progression the same way, which the authors suggest points to other training errors.

A progression pattern that respects this:

1. Increase weekly minutes by about 10 percent for three weeks.
2. Reduce by 20 to 30 percent in week four, keeping one shortened quality session.
3. Repeat, adding volume through frequency and easy-run length rather than through the long run alone.
4. Change one variable per week. Adding a sixth run and extending the long run in the same week is two changes.
5. Hold volume flat during any week with fewer than six hours of average sleep, travel across more than two time zones, or illness.

Structuring the long run

The long run is the single most valuable session in half marathon training, and the easiest to mismanage. Three principles:

Measure it in time, not distance. A 2-hour run costs the same whether it covers 18 km or 23 km, and pacing it by distance pushes slower runners into disproportionate fatigue.

Cap it near 30 percent of weekly volume. A 100-minute long run inside a 45 km week is already a large share of the total. Long runs that reach 40 percent of weekly volume produce the fatigue of a race without the recovery of one.

Add race-pace work from about week 5. The most transferable version is a long run whose second half contains sustained goal-pace work.

Use the long run to rehearse fueling as well. Take 30 to 60 g of carbohydrate per hour after the first 45 minutes, using the exact product you plan to race with, and practise drinking on the move.

Recovery days are a training decision

Recovery runs exist to add aerobic volume at negligible recovery cost. Run them faster and they add fatigue without adding much stimulus. Seiler (2010) found that competitive endurance athletes converge on roughly 80 percent of sessions at low intensity, with little time spent at threshold. Recovery days are where recreational runners break that distribution.

Practical markers for a recovery day:

• Full sentences of speech throughout
• Perceived effort 3 out of 10 or lower
• 30 to 50 minutes, rarely longer
• Flat or gently rolling terrain, chosen so effort stays low
• Legs feel the same or better afterwards

If a recovery run feels hard from the first 10 minutes, cut it to 25 minutes or walk. That decision costs nothing and protects the next quality session.

Sleep and the ceiling on volume

Sleep sets the upper bound on how much training you can convert into fitness. Fullagar and colleagues (2015) reviewed sleep loss in athletes and reported that while some maximal and gross motor efforts can be maintained after sleep restriction, sport-specific performance tends to decline, and reduced sleep quality and quantity can produce autonomic imbalance resembling overtraining symptoms as well as increases in pro-inflammatory cytokines.

For half marathon training, three rules follow:

1. Treat a week of poor sleep as a hold week, not a build week.
2. Schedule the long run on the day after your best sleep opportunity, not the day after your latest night.
3. If sleep is chronically short, add volume through an extra short run rather than by extending the long run, because the long run is the session most sensitive to accumulated fatigue.

Vitadel Run reads sleep and HRV from Apple Health and adjusts each day's session size, which is a reasonable proxy for the judgement call described above.

A 12-week skeleton

This is a five-day structure at roughly 55 to 65 km peak.

• Monday: rest or 30 min easy
• Tuesday: quality 1, threshold work. Weeks 1 to 5: 4 x 8 min at threshold with 2 min jog. Weeks 6 to 10: 2 x 15 min or 25 min continuous
• Wednesday: easy 50 to 65 min
• Thursday: quality 2. Weeks 1 to 5: 6 x 800 m at interval pace. Weeks 6 to 10: 8 to 10 km at goal half pace, or 5 x 1600 m slightly faster than goal pace
• Friday: rest or recovery 30 to 40 min
• Saturday: recovery 40 min with 6 x 20 s hill sprints
• Sunday: long run per the table above

Reduce weeks 4, 8, and 11 by 20 to 30 percent. Weeks 11 and 12 form the taper, with the final week at roughly 55 percent of peak volume.

The midweek medium-long run

The session that most distinguishes a serious half marathon build from a casual one is not a workout at all. It is a 75 to 95 minute easy run in the middle of the week.

It does three things. It roughly doubles the number of long aerobic efforts per week without doubling the recovery cost, since 80 minutes easy is far cheaper than a second long run. It raises weekly volume through duration rather than through an extra day, which suits runners who cannot add a sixth session. And it improves fat oxidation and fuel handling at a duration long enough to matter.

Placement rules:

• Put it on the day furthest from both quality sessions, usually Wednesday in a Tuesday and Thursday quality week
• Keep it entirely easy, with speech possible throughout
• Add 10 minutes every two weeks up to your ceiling, then hold
• Drop it first when readiness is poor, before touching the long run or the quality sessions
• Skip it entirely during reduced weeks

A runner going from 50 to 65 km per week is often better served by extending a midweek run from 50 to 85 minutes than by extending the long run from 110 to 130 minutes, because the second change raises peak single-session fatigue while the first does not.

Race day execution

Pace conservatively for the first 5 km. Half marathons reward negative splits and punish enthusiasm: 10 seconds per kilometre too fast in the first 5 km typically costs 45 to 90 seconds over the final 7 km. Take carbohydrate at 45 and 75 minutes if the race is over 90 minutes, and drink small amounts early rather than large amounts late.

Plan the race in four segments: 0 to 5 km at goal pace minus 3 to 5 seconds per kilometre, 5 to 12 km at goal pace, 12 to 18 km holding form and cadence, and the final 3 km spending whatever remains. If the first segment feels slightly too easy, you have paced it correctly.