Understanding Training Load

Training load is a way to quantify the stress you're placing on your body. By tracking load over time, you can optimize the balance between building fitness and allowing recovery.

The Fitness-Fatigue Model

Your body responds to training through two competing forces:

1. Fitness (CTL - Chronic Training Load): Your accumulated fitness from consistent training over weeks and months
2. Fatigue (ATL - Acute Training Load): Your recent training stress that hasn't yet been absorbed
3. Form (TSB - Training Stress Balance): The difference between fitness and fatigue—your readiness to perform

TSB = CTL - ATL

When TSB is positive, you're fresh and ready to race. When it's negative, you're carrying fatigue (which is necessary for building fitness).

How Training Load Works

Chronic Training Load (CTL) - "Fitness"

CTL represents your long-term training consistency, typically calculated as a 42-day (6-week) rolling average of daily training stress.

What it tells you:

• Your overall fitness level
• How much training your body is adapted to handle
• The baseline from which you're building

Key insight: CTL changes slowly. You can't cram fitness—it requires weeks of consistent work.

Acute Training Load (ATL) - "Fatigue"

ATL represents your recent training stress, typically a 7-day rolling average.

What it tells you:

• How much you've trained recently
• Your current fatigue level
• Whether you need recovery

Key insight: ATL changes quickly. A hard week shows up immediately; a recovery week provides fast relief.

Training Stress Balance (TSB) - "Form"

TSB is the relationship between your fitness and fatigue:

TSB Range	Status	What It Means
+15 to +25	Peak form	Ready for racing, possibly undertrained
+5 to +15	Fresh	Good for key workouts or races
-10 to +5	Neutral	Normal training zone
-10 to -25	Tired	Building fitness, need recovery soon
Below -25	Overreached	High injury/burnout risk

The Training Load Sweet Spot

Building Phase

During base building or race preparation, you want to accumulate "productive fatigue":

• TSB between -10 and -20: Working hard but manageable
• CTL trending upward: Fitness is building
• Regular recovery: Cutback weeks to absorb training

Taper Phase

Before a race, you want to shed fatigue while maintaining fitness:

• TSB climbing toward +10 to +20: Getting fresh
• CTL stable or slightly declining: Fitness maintained
• Reduced volume, maintained intensity: Keep sharpness

Recovery Phase

After a race or hard training block:

• TSB returning to neutral or positive: Absorbing the work
• ATL dropping significantly: Active recovery
• CTL may dip slightly: Normal and expected

Practical Application

Week-to-Week Load Changes

Avoid large jumps in training load:

Load Change	Risk Level
< 10% increase	Low risk
10-15% increase	Moderate—monitor carefully
15-20% increase	High—only with good reason
> 20% increase	Very high—injury likely

The 10% Rule (Refined)

The classic "don't increase mileage by more than 10% per week" is a useful starting point, but context matters:

• New runners: Stick to 10% or less
• Experienced runners: Can handle 15-20% occasionally
• After time off: Reduce to 5-10%
• Adding intensity: Count it as volume increase

Cutback Weeks

Plan regular reductions in training load:

• Every 3-4 weeks: Reduce volume by 20-30%
• Keep some intensity: Maintains fitness while recovering
• Watch TSB: Should move toward neutral or positive

Load vs. Mileage

Mileage alone doesn't tell the whole story. Two 40-mile weeks can have very different loads:

Week A (Lower Load):

• 6 easy runs
• No workouts
• 12-mile long run at easy pace

Week B (Higher Load):

• 4 easy runs
• 1 tempo session
• 1 interval session
• 16-mile long run with race-pace finish

Week B might have the same mileage but 30-40% higher training load due to intensity.

Signs of Excessive Load

Physical Warning Signs

• Persistent fatigue that doesn't improve with rest
• Increased resting heart rate (5-10 beats above normal)
• Recurring minor injuries or niggles
• Decreased performance despite continued training
• Frequent illness

Mental Warning Signs

• Dreading workouts you usually enjoy
• Irritability and mood changes
• Disrupted sleep despite being tired
• Loss of motivation

If you're experiencing these, your training load is likely too high relative to your recovery.

Using This Calculator

This calculator provides a simplified training load estimate based on:

1. Your chronic load baseline (6-week average mileage)
2. Your acute load (this week's mileage and intensity)
3. Long run contribution (disproportionate stress from long efforts)

For more precise tracking, connect your Strava account to get load calculations based on your actual training data.

Integrating with Your Training

Before Key Workouts

Check that your TSB isn't too negative. Hard workouts on accumulated fatigue yield diminishing returns and increase injury risk.

Planning Recovery

After a hard training block, plan enough easy days/weeks for TSB to return toward neutral before the next hard phase.

Race Preparation

Use the Taper Calculator to plan your pre-race volume reduction and watch your TSB climb toward race-ready freshness.

Long-Term Tracking

The real power of training load comes from tracking it over months and years. You'll learn your personal patterns:

• How much load you can handle
• How long you need to recover
• What TSB range produces your best performances