Training load is the total stress placed on the body through exercise. It is determined by three primary variables: volume (how much you run), intensity (how hard you run), and frequency (how often you run). Managing these variables correctly is essential for driving adaptation while avoiding overtraining and injury.
This article defines training load, explains volume, intensity, and frequency, outlines methods for quantification, and provides guidelines for balancing these variables throughout marathon training.
Definition
Training load is the cumulative physiological and biomechanical stress imposed on the body by training. It reflects the overall demand of training sessions and determines the stimulus for adaptation.
Three components define training load:
- Volume: Total amount of training (distance or time)
- Intensity: Effort level or pace
- Frequency: Number of training sessions per week
Key principle: Adaptation occurs when training load is sufficient to challenge the body but not so excessive that recovery is compromised.
Volume: How much you run
Definition
Volume is the total amount of running performed, typically measured as:
- Weekly mileage (most common)
- Monthly or yearly mileage
- Time spent running (useful for beginners or varied paces)
Why volume matters
Aerobic adaptations:
- High volume builds the aerobic base
- Drives mitochondrial density and capillary growth
- Improves fat oxidation and endurance
Muscle and connective tissue strengthening:
- Consistent volume strengthens muscles, tendons, and ligaments over time
- Reduces injury risk when built gradually
Running economy:
- More time on feet refines mechanics and efficiency
Typical volume ranges
Beginner marathoners:
- 20-35 miles per week at peak
Intermediate marathoners:
- 35-50 miles per week at peak
Advanced marathoners:
- 50-70+ miles per week at peak
Elite marathoners:
- 80-120+ miles per week
Volume progression
Best practice: Increase weekly volume by no more than 10% per week, with a recovery week (reduced volume) every 3-4 weeks.
Example progression:
- Week 1: 30 miles
- Week 2: 33 miles
- Week 3: 36 miles
- Week 4: 27 miles (recovery week)
- Week 5: 38 miles
Intensity: How hard you run
Definition
Intensity is the effort level or pace of a training session, ranging from very easy to maximal.
Common intensity categories:
- Easy / Recovery: Conversational pace, 60-75% max HR
- Moderate / Steady: Comfortably hard, 75-85% max HR
- Threshold / Tempo: Sustainably hard, 85-90% max HR
- VO₂max / Intervals: Hard, 90-100% max HR
Why intensity matters
Specific adaptations:
- Easy intensity builds aerobic base
- Threshold intensity raises lactate threshold
- High intensity improves VO₂max
Training stress:
- Higher intensity increases fatigue and recovery demands
- Low-intensity training allows higher volume with less breakdown
The 80/20 rule
Principle: Approximately 80% of training volume should be at low intensity (easy pace), with 20% at moderate to high intensity.
Rationale:
- Most aerobic adaptations occur at easy paces
- Excessive intensity limits total volume and increases injury risk
- High volume of easy running builds durability and endurance
Intensity distribution in marathon training
Base phase:
- 85-90% easy
- 10-15% moderate to threshold
Build phase:
- 75-80% easy
- 20-25% moderate to high intensity
Peak phase:
- 70-75% easy
- 25-30% moderate to high intensity (including race-pace work)
Frequency: How often you run
Definition
Frequency is the number of running sessions per week.
Typical frequencies:
- Beginner runners: 3-4 days per week
- Intermediate runners: 4-5 days per week
- Advanced runners: 5-6 days per week
- Elite runners: 6-7 days per week (sometimes multiple sessions per day)
Why frequency matters
Consistency:
- More frequent sessions maintain stimulus for adaptation
- Spreads volume across more days, reducing per-session stress
Recovery:
- Too many sessions limit recovery time
- Fewer sessions allow greater recovery between efforts
Practical considerations:
- Balances training with work, family, and life commitments
Optimal frequency for marathon training
General guideline: 4-6 days per week for most marathoners
Trade-offs:
- Higher frequency (6-7 days): Allows more volume but requires excellent recovery practices
- Moderate frequency (4-5 days): Balances training stimulus with recovery
- Lower frequency (3 days): Suitable for beginners or when constrained by time
Best practice: Include at least one full rest day per week to support recovery and adaptation.
Quantifying training load
Methods to measure training load
Training load can be quantified using several approaches:
1. Volume alone (mileage or time)
Pros: Simple, easy to track Cons: Ignores intensity; 10 easy miles ≠ 10 hard miles
2. Rate of Perceived Exertion (RPE)
Scale: 1-10, where 1 is very easy and 10 is maximal effort
Session RPE (sRPE):
- Multiply average RPE by session duration (minutes)
- Example: 60-minute run at RPE 6 = 360 load units
Pros: Accounts for intensity, simple, no equipment needed Cons: Subjective, varies day to day
3. Heart rate-based metrics
Training Impulse (TRIMP):
- Combines heart rate intensity and duration
- Requires heart rate monitor
Pros: Objective, accounts for intensity Cons: Requires equipment, influenced by external factors (heat, fatigue, caffeine)
4. Pace-based zones
Approach:
- Assign zones based on pace relative to race goals or thresholds
- Track time or distance in each zone
Pros: Sport-specific, easy to implement Cons: Pace affected by terrain, weather, fatigue
5. Running power meters
Approach:
- Measures mechanical power output (watts)
- Accounts for terrain and conditions
Pros: Objective, accounts for hills and wind Cons: Requires specialized equipment, relatively new metric
Balancing volume, intensity, and frequency
The training load triangle
Volume, intensity, and frequency interact in complex ways:
- Increase volume: May require reducing intensity or frequency
- Increase intensity: Often requires reducing volume or adding rest days
- Increase frequency: May limit per-session volume or intensity
Golden rule: Change only one variable at a time.
Typical progressions
Early base phase:
- Focus: Build volume and frequency
- Strategy: Keep intensity low, gradually add mileage
Mid-base to build phase:
- Focus: Add moderate intensity
- Strategy: Maintain volume, introduce tempo and threshold work
Peak phase:
- Focus: Fine-tune race-specific intensity
- Strategy: Maintain or slightly reduce volume, add targeted race-pace efforts
Taper phase:
- Focus: Recover while maintaining sharpness
- Strategy: Reduce volume significantly, maintain some intensity
Common mistakes
Too much intensity too soon
Problem: Beginners often run too hard on easy days Result: Incomplete recovery, inability to train hard on quality days, increased injury risk
Solution: Follow the 80/20 rule strictly
Increasing volume and intensity simultaneously
Problem: Adding mileage while also increasing workout intensity Result: Overtraining, injury, burnout
Solution: Build volume first, then layer intensity gradually
Neglecting recovery
Problem: Running too many days without adequate rest Result: Chronic fatigue, diminished adaptation
Solution: Schedule at least one full rest day per week; include easy weeks every 3-4 weeks
Ignoring individual response
Problem: Blindly following plans without adjusting for personal recovery Result: Overtraining or undertraining
Solution: Monitor fatigue, sleep quality, motivation, and performance; adjust training accordingly
Practical guidelines
For beginners
- Volume: Start at 15-20 miles/week, build gradually
- Intensity: 85-90% easy running
- Frequency: 3-4 days/week with rest days between runs
For intermediate runners
- Volume: 30-50 miles/week at peak
- Intensity: 75-80% easy, 20-25% moderate to hard
- Frequency: 4-5 days/week, include one quality session and one long run
For advanced runners
- Volume: 50-70+ miles/week at peak
- Intensity: 70-75% easy, 25-30% moderate to hard
- Frequency: 5-6 days/week, include two quality sessions and one long run
Monitoring weekly load
Track:
- Total weekly mileage
- Number of hard sessions (threshold, intervals, long runs)
- Subjective fatigue levels (RPE or mood)
Warning signs of excessive load:
- Persistent fatigue
- Declining performance
- Elevated resting heart rate
- Poor sleep quality
- Loss of motivation
Response: Reduce volume, intensity, or frequency; add extra rest days
Summary
Training load is the total stress imposed by training, determined by volume (how much), intensity (how hard), and frequency (how often). Volume drives aerobic base development and endurance; intensity targets specific adaptations like lactate threshold and VO₂max; frequency balances training stimulus with recovery. Effective marathon training follows the 80/20 principle, with most volume at easy intensity and limited high-intensity work. Training load can be quantified using mileage, RPE, heart rate metrics, pace zones, or power. Balancing these variables requires changing only one at a time, progressing gradually, and monitoring individual response. Common mistakes include excessive intensity, increasing multiple variables simultaneously, and neglecting recovery. Successful marathon training tailors volume, intensity, and frequency to individual capacity while respecting the principle that adaptation requires both stress and recovery.