Training

The half marathon is an unusual distance: long enough that aerobic base and fueling matter, short enough that lactate threshold pace is the primary performance limiter. It demands more sustained threshold work than marathon training but less weekly volume. Athletes who train for it like a marathon run too slowly. Those who train like it's a 10K run too hard. Here's the structure the evidence supports.

The Physiology of Half Marathon Racing

A half marathon is run at approximately 85–92% of VO2max for competitive runners — above lactate threshold for most of the race. For recreational runners (90–120 minute finish), the intensity is closer to 80–87% of VO2max — below lactate threshold for much of the race, but not by much.

The primary limiters in half marathon performance:

1. Lactate threshold pace — the pace you can sustain before lactate accumulates. Raising this directly raises your half marathon ceiling.
2. VO2max — sets the upper limit of aerobic capacity. Interval training at 5K effort develops this.
3. Running economy — the oxygen cost per unit of distance. Strength training and high mileage improve this.
4. Aerobic base — supports recovery between sessions and enables high-quality threshold work.

The 12-Week Structure

Phase 1 — Base and Threshold Introduction (Weeks 1–4)

Establish mileage, introduce threshold work. This phase builds the aerobic infrastructure everything else requires.

• Weekly volume: 40–55km (depending on starting fitness). Increase by no more than 10% per week.
• Long run: 18–22km at easy pace. Weekly priority.
• Threshold session (1×/week): 2–3 × 10 minutes at threshold pace with 2-minute jog recovery. Progress to 20 minutes continuous by end of phase.
• Easy running: All other sessions at genuinely easy pace.
• Strides: 4–6 × 100m at slightly faster than 5K pace twice weekly. Maintains neuromuscular efficiency without adding meaningful training stress.

Phase 2 — Threshold and VO2max Development (Weeks 5–9)

The primary adaptation phase. Threshold capacity and aerobic ceiling both develop simultaneously.

• Weekly volume: 50–65km. One down week at 40% volume reduction at week 7.
• Long run: 22–26km, with the final 5–8km at marathon pace or slightly faster.
• Threshold session (1×/week): 25–35 minutes continuous at threshold, or 4 × 12 minutes with 2-minute jog.
• Interval session (1×/week): 5–6 × 1000m at 5K pace with 90-second recovery. Develops the VO2max ceiling that half marathon pace draws from.
• Easy running: All other sessions genuinely easy. No moderate pace.

Phase 3 — Race-Specific Work and Taper (Weeks 10–12)

Specificity increases. Threshold pace becomes goal half marathon pace or slightly faster.

• Week 10: Half-marathon specific: 6 × 1.5km at goal half marathon pace; 90-second recovery. One 24km long run.
• Week 11: Volume drops 30%. One quality session: 3 × 10 minutes at threshold with easy surroundings. Long run 18km easy.
• Week 12: Race week. Tuesday: 5km with 3km at goal half marathon pace. Thursday: 20-minute easy + 6 strides. Saturday: 15-minute shake-out. Sunday: race.

The Most Common Half Marathon Training Mistakes

• Long runs too fast: Easy-pace long runs build aerobic base. Running them at moderate pace accumulates fatigue without additional adaptation benefit.
• Threshold sessions too hard: Threshold is comfortably hard — not suffering. Blowing up in the first 10 minutes of a 30-minute tempo run defeats the purpose. Start conservative.
• Skipping the interval session: Many half marathon training plans omit VO2max work entirely, focusing only on threshold. But the interval session provides the aerobic ceiling that makes threshold pace sustainable.
• Racing too hard in tune-up events: A B-race 3 weeks out should be run at 90% effort — not a PR attempt. Full race efforts require 2-week recovery; that's time you don't have in a 12-week build.

Nutrition for Half Marathon Training

Fueling strategy for the half marathon differs by finish time:

• Sub-90 minutes: 1 gel at 45–60 minutes is sufficient for most runners. Glycogen depletion is not typically limiting at sub-90-minute effort.
• 90–120 minutes: 2 gels — one at 45 minutes, one at 75–80 minutes. Start early before depletion begins.
• Over 120 minutes: 3 gels at 45, 75, and 95 minutes. Also consider sports drink at aid stations for additional carbohydrate.

Use the NorthLine Running Pace Calculator to derive your threshold, interval, and easy paces from your current 5K or 10K race time — then anchor all training sessions to these calculated targets rather than perceived effort alone.