Numbers don't lie—but you have to understand what they're saying.

Training load metrics help you answer: Am I training enough? Too much? Ready to race?

The Fitness-Fatigue Model

The Basic Concept

Training creates two responses:

1. Fitness (positive training effect)
2. Fatigue (negative, but temporary)

Your current "form" is fitness minus fatigue.

After a hard training block:

• High fitness + high fatigue = tired but fit
• Taper reduces fatigue faster than fitness decays
• Result: peak form for racing

Quantifying It

Training load metrics attempt to measure this:

• CTL = Chronic Training Load (fitness)
• ATL = Acute Training Load (fatigue)
• TSB = Training Stress Balance (form)

CTL: Chronic Training Load (Fitness)

What It Measures

CTL represents your accumulated fitness—the long-term average of your training stress.

Calculated as: ~42-day exponentially weighted average of daily training stress

Interpretation

Guidelines

• CTL should rise gradually during build phases
• Rapid CTL increases risk overtraining
• CTL doesn't capture all fitness aspects (speed, economy, etc.)

ATL: Acute Training Load (Fatigue)

What It Measures

ATL represents recent training stress—short-term fatigue.

Calculated as: ~7-day exponentially weighted average of daily training stress

Interpretation

Guidelines

• ATL responds quickly to training changes
• High ATL without recovery leads to overtraining
• ATL drops quickly during taper

TSB: Training Stress Balance (Form)

What It Measures

TSB = CTL - ATL

This represents your current "form"—how ready you are to perform.

Interpretation

Race Day Targets

For racing at peak form:

• TSB of +5 to +25 is common target
• Too positive (>30) = undertrained
• Negative = still carrying fatigue

During training:

• Negative TSB is normal and necessary
• TSB of -10 to -30 during build phases
• Deeper than -30 risks overtraining

Practical Application

During Base Building

• CTL rising gradually (3-5 points per week max)
• ATL fluctuating with training load
• TSB slightly negative to moderately negative

During Build Phase

• CTL rising more aggressively
• ATL elevated
• TSB moderately negative (-10 to -30)

During Taper

• CTL stable or slightly declining
• ATL dropping rapidly
• TSB rising toward positive territory

Race Week

• CTL maintained by reduced but purposeful training
• ATL low from reduced volume
• TSB positive (target: +5 to +20)

Example Training Cycle

Limitations

What These Metrics Miss

• Intensity specificity: All stress counts equally
• Life stress: Work, sleep, relationships affect recovery
• Individual variation: Same numbers mean different things
• Skill development: Running economy, form improvements

When to Ignore the Numbers

• If you feel terrible despite good TSB
• If you feel great despite negative TSB
• When metrics conflict with performance indicators
• During illness or unusual life circumstances

Listen to your body alongside the data.

Getting Started

Track Your Training

Use platforms that calculate these metrics:

• TrainingPeaks (industry standard)
• Strava (limited features)
• Garmin Connect
• Training analysis platforms

Establish Baselines

• What's your typical CTL when fit?
• What TSB range leaves you feeling good?
• How do your metrics correlate with performance?

Make Gradual Adjustments

Don't chase specific numbers immediately. Use metrics to:

• Prevent overtraining
• Time your taper appropriately
• Understand your personal patterns

Training load metrics add objectivity to training decisions. Use our Training Load Calculator to analyze your training, and track your fitness-fatigue balance on your dashboard.