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 about 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 hold for an hour to ninety minutes, so aerobic durability rather than top-end speed decides the outcome. A runner with a fast 5K and 22 miles a week will usually lose to a runner with a slower 5K and 45 miles a week over 13.1 miles, because the second runner's pace decays less over the final third.

Weekly volume builds the 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 degrades. Those adaptations respond to repeated moderate stress over weeks. No single session substitutes for them.

Gabbett (2016) adds the risk side. Injuries follow rapid load increases and poor programming rather than high load itself, and athletes used to high chronic loads tend to get injured less than those training at lower workloads. The goal is high volume arrived at slowly.

Volume targets by goal

Two caveats. These are peaks for a 12 to 16 week build, not starting points. If you run 20 miles a week now, a 12-week build reaching 35 miles is reasonable and reaching 50 is not. And the top of each range assumes you are sleeping and eating enough, because volume without recovery capacity is accumulated fatigue.

How to raise mileage without a setback

Nielsen and colleagues (2014) provide the clearest data on recreational runners. They followed 874 novice runners for a year with GPS watches, and 202 sustained a running-related injury. Runners who raised 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, and patellar tendinopathy, than runners who progressed by less than 10 percent. 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 that respects this:

1. Raise 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 a week. Adding a sixth run and extending the long run in the same week is two changes.
5. Hold volume flat in any week with under six hours of average sleep, travel across more than two time zones, or illness.

Structuring the long run

The long run is the most valuable session in half marathon training and the easiest to mismanage.

Measure it in time, not distance. A 2-hour run costs the same whether it covers 11 miles or 14, 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 28-mile week is already a large share. 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 running.

Use the long run to rehearse fueling as well. Once the run passes about 90 minutes, take carbohydrate from the products you plan to race with and practice drinking on the move. The marathon fueling guide covers how much and when, and the same numbers apply to a long half marathon.

Recovery days are a training decision

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

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 afterward

If a recovery run feels hard from the first 10 minutes, cut it to 25 minutes or walk. That costs nothing and protects the next quality session. The easy runs guide covers the talk test in detail.

Sleep sets the ceiling on volume

Fullagar and colleagues (2015) reviewed sleep loss in athletes and reported that while some maximal efforts survive sleep restriction, sport-specific performance tends to decline, and reduced sleep can produce autonomic imbalance resembling overtraining. For half marathon training, three rules follow. Treat a week of poor sleep as a hold week. Schedule the long run after your best sleep opportunity, not your latest night. 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, HRV, and resting heart rate from Apple Health and shrinks each day's session when they say to, which is the same judgment call made automatically. Readiness scores explained covers how.

A 12-week skeleton

A five-day structure peaking at about 35 to 40 miles (55 to 65 km).

• Monday: rest or 30 min easy
• Tuesday: quality 1, threshold. 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, extending toward a medium-long run
• Thursday: quality 2. Weeks 1 to 5: 6 x 800 m at interval pace. Weeks 6 to 10: 5 to 6 miles (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 about 55 percent of peak volume.

The midweek medium-long run

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

It roughly doubles the number of long aerobic efforts a 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 an extra day, which suits runners who cannot add a sixth session. And it improves fuel handling at a duration long enough to matter.

Put it on the day furthest from both quality sessions, usually Wednesday in a Tuesday and Thursday quality week. Keep it entirely easy. 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 in reduced weeks.

A runner going from 30 to 40 miles a 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 and the first does not.

Race day

Pace conservatively for the first 3 miles. Half marathons reward even or slightly negative splits and punish enthusiasm. Plan the race in four segments: the first 3 miles at goal pace minus 5 to 8 seconds per mile, miles 3 to 7.5 at goal pace, miles 7.5 to 11 holding form and cadence, and the last 2 miles spending whatever remains. If the first segment feels slightly too easy, you have paced it correctly. The race-day pacing guide covers goal pace, heat, and hills.