Half-Marathon Training Periodization: Transitioning Through Base, Build, and Race Phases

Introduction

“Periodization” is a core concept in competitive sports training, referring to the systematic division of a training plan into distinct phases, each with its own training focus, allowing athletes to reach peak fitness for their most important races. For half marathon runners, periodized training not only maximizes race performance but, more importantly, reduces the risk of overtraining and injury through a planned “stimulus–recovery–adaptation” cycle.

The Three Major Phases of Half Marathon Periodization

1. Base Phase (General Preparation Phase)

Duration: Weeks 1–4 of a 12-week plan
Core Objective: Build an aerobic foundation, establish training habits, and strengthen the musculoskeletal system

The base phase can be likened to “laying the foundation of a house.” Without a solid foundation, later high-intensity training increases the risk of injury. Key characteristics of this phase:

• Low intensity: More than 80% of mileage is in the easy aerobic zone (65–75% of maximum heart rate)
• Gradual mileage increase: Weekly mileage increases by 10%, rising from 25–30 km to 38–42 km
• No specific speed workouts: The only intensity session is 1–2 light tempo runs of 20–30 minutes per week

2. Build Phase (Specific Preparation Phase)

Duration: Weeks 5–9 of a 12-week plan
Core Objective: Improve threshold speed, increase long run distance, and introduce interval training

The build phase is where training yields the most significant gains, but it is also the period with the highest risk of overtraining. Characteristics:

• Increased intensity: Threshold workouts (tempo runs) account for 15–20%, intervals 10–15%
• Long run distance peaks: The longest run reaches 20–22 km in week 9
• A deload week every 4 weeks: Mileage drops to 70% of the previous week, allowing the body to supercompensate

3. Race Phase (Competition Phase / Taper)

Duration: Weeks 10–12 of a 12-week plan
Core Objective: Maintain speed sensation, eliminate fatigue, and bring the body to a peak state

Detailed Comparison of the Three Phases

Timing and Signals for Phase Transitions

Phase transitions should not be followed mechanically by the calendar; the following signals are important indicators for transitioning:

Conditions for Base → Build Phase:

• Can easily run 14–16 km continuously without feeling particularly fatigued
• Weekly training is executed consistently, with no pain or repetitive discomfort
• Easy pace naturally improves (without forcing, pace is 10–15 seconds faster than at the start of training)

Conditions for Build → Race Phase:

• Have completed 2–3 long runs of 18–22 km
• The last 2 intervals in interval workouts show no significant slowdown (< 5-second drop-off)
• 2–3 weeks remain until the target race

Common Mistakes in Training Periodization

• Skipping the base phase: Rushing into interval training without aerobic base support yields poor results and increases injury risk
• Not scheduling deload weeks in the build phase: After 4–5 consecutive weeks of high intensity, overtraining syndrome (persistent fatigue, declining pace) is only a matter of time
• Training too much during the race phase: “One more long run before the race to top up training volume” is a common mistake that ruins the taper effect
• Following the calendar rather than how you feel: If the body is particularly fatigued, the build phase can be extended by 1–2 weeks, and the race phase appropriately shortened

How to Design a Personalized Periodized Plan

Steps are as follows:

1. Confirm the target race date
2. Count back 12 weeks and mark the training start date
3. Weeks 1–4 = Base Phase; Weeks 5–9 = Build Phase; Weeks 10–12 = Race Phase
4. Schedule a “deload week” every 4 weeks (reduce mileage by 30%)
5. No intervals in the base phase; introduce 1000m repeats only in weeks 5–6 of the build phase

Practical Advice

• Use a “training log app” (such as TrainingPeaks, Garmin Connect) to track weekly “Training Stress Score (TSS)” and visualize the load changes across each phase
• If morning resting heart rate rises more than 7–8 bpm for 3 consecutive days during the build phase, proactively schedule an extra recovery day
• The base phase can align with Taiwan’s climate: build the foundation in late summer (August–September), the build phase in autumn/winter (October–December), and the race phase in late winter (January–March)

Conclusion

The essence of periodized training is “making the right things happen at the right time.” Patience in the base phase, diligence in the build phase, and wisdom in the race phase—all three are indispensable. For your next race preparation, start by confirming the race date, count down, and give every week of training a clear purpose.

Related Reading

• Full Marathon Periodized Training: The Four Phases of Base, Build, Race, and Recovery
• Road Running Periodization Basics: Time Allocation for Base, Strength, Peak, and Recovery Phases
• The Complete Guide to Periodized Training: How to Scientifically Plan Your Annual Training Program
• Road Running Periodization for Beginners: The Three-Stage Structure of Base, Build, and Pre-Race