Half-Marathon Training Long Runs: Pacing for a Weekly 18–22 km Session

Introduction

Ask any half-marathon coach: “Which workout is the most important in training?” Nine times out of ten, the answer is the Long Run. A weekly long, slow distance run is the core method for building your aerobic base, improving fat-burning efficiency, and strengthening musculoskeletal tolerance. However, many runners either run their long runs too fast (accumulating fatigue) or too slow (insufficient stimulus). This article breaks down precise pacing for 18–22 km long runs for half-marathon goal runners.

The Physiological Goals of the Long Run

The physiological adaptations from half-marathon long runs include:

• Increased mitochondrial density: More “cellular power plants” improve aerobic metabolic efficiency
• Capillary growth: More capillaries in the muscles improve oxygen transport efficiency
• Increased muscle glycogen stores: Prolonged exercise gradually depletes liver glycogen, stimulating the body to store more
• Improved fat utilization: Low-intensity, long-duration training teaches the body to burn fat preferentially, preserving glycogen
• Tendon and bone tolerance: Gradually adapting to the cumulative impact of long distances

The Golden Rule of Pacing

The fundamental principle of the long run is “easy but effective,” typically recommended at a pace 60–90 seconds/km slower than your goal half-marathon pace.

Heart Rate Reference: Throughout the long run, your heart rate should stay at 65–75% of your maximum heart rate, maintaining a state of “slightly breathless but able to hold a conversation.”

Pacing Variations for Three Long Run Formats

Format 1: Easy Long Run

When to use: First 4–5 weeks of the training cycle, recovery weeks, or when fatigue levels are high

Maintain a slow pace throughout, 90+ seconds slower than your goal race pace. Taiwan’s riverside trails are excellent venues—the flat terrain keeps your pace steady and makes it easy to set up aid stations.

Format 2: Progression Long Run

When to use: Build phase (weeks 5–9 of the training cycle)

• First 2/3: Easy pace (90 seconds slower than race pace)
• Last 1/3: Gradually increase to goal half-marathon pace or even slightly faster

Example (20 km, 2:00 goal):

• First 13 km: 6:40/km
• Last 7 km: 5:45–5:50/km

Format 3: Specific Long Run

When to use: 4–6 weeks before race day, simulating race conditions

• Warm-up 4 km: Easy
• Middle 14 km: Goal half-marathon pace ± 5 seconds
• Final 4 km: Increase to threshold pace

This is the highest-intensity format of the three; do not do it more than twice per month.

Long Run Nutrition and Hydration Management

Long runs over 18 km require proactive fueling:

• Hydrate every 5 km: Don’t wait until you’re thirsty
• Consume carbs after 75 minutes: Gels (30–45g carbs) or bananas both work
• Special note for Taiwan summers: When temperatures exceed 28°C, you can loosen your long run pace by 10–20 seconds and shorten the distance to 16–18 km

Common long run fueling strategies in Taiwan:

• Pre-plan stops at convenience stores along the route to quickly buy a drink and keep running
• Carry a soft flask belt (500 ml + 2 gels)
• Start at 5–6 AM to take advantage of the cooler morning temperatures and lighter traffic

Long Run Recovery Management

• Refuel immediately after finishing: consume carbs (banana + sports drink) and protein (soy milk or tea egg) within 15 minutes
• Do no other high-intensity training that day
• The next day, schedule a very easy 6–8 km recovery run (heart rate below 70% of max HR)

Practical Tips

• For long runs, tracking “time” rather than pace is more scientific: a runner targeting 2 hours should do long runs of 100–110 minutes, as physiological stimulus is more directly related to time
• Increase long run distance by 1–2 km every 2–3 weeks; don’t jump up too much at once
• If you experience unusual knee or calf pain after a long run, immediately shorten the distance and assess whether rest is needed
• Choosing shaded routes (such as around Daan Forest Park or near Bitan) can reduce the impact of Taiwan’s summer radiant heat

Conclusion

Pacing control on the long run is an art—running “slow enough” is often harder than running “fast enough.” Every easy 18–22 km long run is meant to help you cover the full race distance faster on race day. Make the long run the workout you look forward to most each week, not the challenge you dread.

Related Reading

• Executing the Long Run Correctly: Pace, Distance, and Frequency
• Long Run Pacing: The Long-Term Benefits of Running Conservatively
• Marathon Long Run Training Strategies: A Scientific Approach to Building Distance
• Designing Your Long Run: Weekly Distance, Pace, and Fueling Strategies