Load Management

Training Stress Score (TSS) Calculation Guide

How to quantify training load across different sports using the TSS methodology

What Is Training Stress Score (TSS)?

Training Stress Score (TSS) is a metric developed by TrainingPeaks and Dr. Andrew Coggan that quantifies the training load of a single session by combining duration and intensity. Unlike simple duration or distance metrics, TSS accounts for how hard you worked relative to your threshold capacity.

TSS is the foundation for calculating Chronic Training Load (CTL/Fitness), Acute Training Load (ATL/Fatigue), and Training Stress Balance (TSB/Form)—the Performance Manager Chart metrics used for load governance.

The Core TSS Equation

TSS = (Duration in seconds × Normalized Power × Intensity Factor) / (FTP × 3600) × 100

Simplified: TSS combines how long and how hard. A 1-hour session at threshold (IF = 1.0) produces exactly 100 TSS by definition.

Key Concepts for TSS Calculation

1. Functional Threshold (FTP/FTPace/Threshold HR)

Your threshold is the baseline against which intensity is measured:

Cycling: Functional Threshold Power (FTP in watts)
Running: Functional Threshold Pace (FTPace in min/km)
Swimming: Threshold pace (CSS/T-pace)
Heart Rate-based: Lactate Threshold Heart Rate (LTHR)

2. Intensity Factor (IF)

IF = Normalized Power / FTP (for power-based sports)
IF = Average HR / Threshold HR (for HR-based estimation)

IF = 0.50-0.65: Recovery/easy aerobic
IF = 0.65-0.85: Endurance/tempo
IF = 0.85-0.95: Threshold work
IF = 0.95-1.05: VO2max intervals
IF > 1.05: Anaerobic capacity/sprint work

3. Duration

Time spent training in seconds or hours. Longer sessions at the same intensity produce higher TSS.

Sport-Specific TSS Calculations

Cycling (Power-Based)

Most accurate when using a power meter:

TSS = (Duration_seconds × NP × IF) / (FTP × 3600) × 100

Example:

• 2-hour ride (7200 seconds)
• Normalized Power (NP) = 220W
• FTP = 250W
• IF = 220/250 = 0.88
• TSS = (7200 × 220 × 0.88) / (250 × 3600) × 100 = 154 TSS

Running (Pace or HR-Based)

Use Running TSS (rTSS) based on pace or heart rate:

rTSS = Duration_hours × 100 × IF²

Example (Pace-based):

• 90-minute run (1.5 hours)
• Average pace = 4:30 min/km
• Threshold pace = 4:00 min/km
• IF = 4:00 / 4:30 = 0.89
• rTSS = 1.5 × 100 × 0.89² = 119 TSS

Swimming (Pace-Based)

Swimming TSS (sTSS) uses CSS (Critical Swim Speed) or T-pace:

sTSS = Duration_hours × 100 × IF²

Example:

• 60-minute swim (1.0 hour)
• Average pace = 1:25/100m
• CSS/T-pace = 1:20/100m
• IF = 1:20 / 1:25 = 0.94
• sTSS = 1.0 × 100 × 0.94² = 88 TSS

Heart Rate-Based TSS (hrTSS)

When power/pace unavailable, use heart rate (less accurate but useful):

hrTSS = Duration_hours × 100 × IF²

Where IF = Average HR / Lactate Threshold HR

Note: HR lags effort, so hrTSS underestimates high-intensity intervals.

RPE-Based TSS Estimation (Session RPE)

When no objective metrics are available, use Rate of Perceived Exertion (RPE) on a 1-10 scale:

TSS ≈ Duration_minutes × RPE × 1.5

Example:

• 90-minute strength session, RPE = 7
• TSS ≈ 90 × 7 × 1.5 = ~95 TSS

* This is less precise but useful for non-endurance training (strength, yoga, etc.)

Typical TSS Values by Session Type

Easy/Recovery Sessions

30-50 TSS (1-1.5 hours at low intensity)

Endurance/Base Training

60-120 TSS (2-3 hours moderate intensity)

Threshold/Tempo Workouts

80-150 TSS (1-2 hours with intervals)

High-Intensity Interval Sessions

40-80 TSS (shorter, very hard efforts)

Long Endurance Rides/Runs

150-300 TSS (4-6 hours steady effort)

Race Simulation

200-400+ TSS (race-intensity efforts)

Weekly TSS Targets by Training Level

Beginner/Recreational200-400 TSS/week

Intermediate/Competitive400-700 TSS/week

Advanced/Elite700-1200+ TSS/week

* These are general guidelines. Individual tolerance varies based on training history, recovery capacity, and life stress.

Using TSS for Load Management

TSS becomes powerful when aggregated into Performance Manager Chart metrics:

CTL (Chronic Training Load):
42-day rolling average of daily TSS. Represents fitness.
ATL (Acute Training Load):
7-day rolling average of daily TSS. Represents fatigue.
TSB (Training Stress Balance):
CTL - ATL. Positive = fresh, negative = fatigued.

Key Takeaways

TSS quantifies training load by combining duration and intensity
100 TSS = 1 hour at threshold by definition
Power-based TSS is most accurate; HR and RPE are proxies
Track TSS to monitor trends in CTL, ATL, and TSB for load governance
Weekly TSS should align with your training phase and experience level

Further Resources

• Coggan, A. & Allen, H. (2010). Training and Racing with a Power Meter. VeloPress.
• TrainingPeaks University: Performance Management Chart course
• Friel, J. (2018). The Triathlete's Training Bible. VeloPress.