Training Stress Score (TSS): What is 100 TSS and How to Use It

What is 100 TSS?

A 100 TSS (Training Stress Score) represents the physiological stress equivalent to one hour of continuous exercise performed at your maximum sustainable power output or pace, often referred to as Functional Threshold Power (FTP) for cycling or Functional Threshold Pace (rFTP) for running.

Understanding Training Stress Score (TSS)

The Training Stress Score (TSS) is a widely used metric in endurance sports, particularly cycling and running, to quantify the physiological stress and training load of a specific workout. Developed by Dr. Andrew Coggan and Hunter Allen, TSS provides a single number that reflects both the intensity and duration of an exercise session, allowing athletes and coaches to objectively track training volume and recovery needs.

TSS is calculated using a proprietary algorithm that considers three key variables:

• Normalized Power (NP) or Normalized Graded Pace (NGP): This is a power or pace metric that accounts for the physiological cost of fluctuating intensities during a workout, providing a more accurate representation of the effort than simple average power or pace.
• Intensity Factor (IF): This is a ratio of your Normalized Power (or NGP) to your Functional Threshold Power (FTP) or Functional Threshold Pace (rFTP). It quantifies the intensity of a workout relative to your individual threshold. An IF of 1.0 means you are exercising at your threshold.
• Duration: The total time spent exercising in minutes.

The fundamental concept behind TSS is that training stress is not just about how long you exercise, but also how hard. A short, high-intensity interval session can generate as much, or even more, training stress than a longer, lower-intensity endurance ride.

The Significance of a 100 TSS Score

When an athlete achieves a 100 TSS score in a single workout, it carries a very specific meaning within the training load paradigm:

• The Benchmark: A 100 TSS workout is defined as precisely one hour of exercise performed at an Intensity Factor (IF) of 1.0. This means the athlete sustained their Functional Threshold Power (FTP) or Functional Threshold Pace (rFTP) for the entire 60 minutes.
• Physiological Impact: This level of effort represents a significant physiological challenge, pushing the athlete to their aerobic limits for an extended period. It is a demanding workout that requires substantial recovery.
• Contextual Understanding: While 100 TSS is the benchmark for an hour at threshold, it's crucial to understand that it can be achieved in various ways:
  • High Intensity, Shorter Duration: A very hard, shorter workout (e.g., 30 minutes at an IF of 1.41) could also yield approximately 100 TSS.
  • Lower Intensity, Longer Duration: A much longer, lower-intensity endurance session (e.g., 3-4 hours at an IF of 0.5-0.6) could also accumulate 100 TSS or more.

Therefore, "100 TSS" is less about the absolute number and more about the relative effort required to achieve it, with the 1-hour threshold effort serving as the standard reference point.

Why Track TSS? The Benefits for Athletes and Coaches

Tracking TSS offers numerous advantages for optimizing training and preventing common pitfalls:

• Quantifying Training Load: TSS provides an objective, standardized metric to measure the physiological stress of each workout, making it easy to compare different sessions.
• Avoiding Overtraining: By monitoring cumulative TSS (e.g., weekly or monthly totals), athletes and coaches can identify when training load is becoming excessive, helping to prevent burnout, injury, and overtraining syndrome.
• Optimizing Recovery: Understanding the stress generated by a workout allows for more precise recovery planning. A high TSS workout demands more recovery time than a low TSS session.
• Guiding Periodization and Progression: TSS is a cornerstone of effective training periodization. Coaches can manipulate TSS targets to build fitness during base phases, intensify during build phases, and reduce stress during taper phases. It helps ensure a progressive overload that drives adaptation.
• Performance Prediction and Management: TSS forms the basis for more advanced training metrics used in platforms like TrainingPeaks:
  • Chronic Training Load (CTL): A rolling 42-day average of daily TSS, representing an athlete's fitness or "form." Higher CTL generally indicates greater fitness.
  • Acute Training Load (ATL): A rolling 7-day average of daily TSS, representing recent fatigue.
  • Training Stress Balance (TSB): The difference between CTL and ATL (CTL - ATL). A positive TSB typically indicates readiness for performance, while a negative TSB suggests accumulated fatigue.

Limitations and Considerations of TSS

While TSS is an invaluable tool, it's important to acknowledge its limitations and use it within context:

• Individual Variability: TSS is based on an individual's FTP or rFTP, but it doesn't account for individual differences in recovery capacity, sleep quality, nutrition, or external life stressors. Two athletes might accumulate 100 TSS, but experience vastly different levels of fatigue.
• Context is Key: A 100 TSS workout for a beginner athlete might be an incredibly challenging, season-defining effort, while for an elite professional, it could be a routine daily workout. The meaning of the number is relative to the athlete's fitness level.
• Accuracy of Thresholds: TSS calculations are highly dependent on accurate and up-to-date FTP or rFTP values. If your threshold is incorrectly set, your TSS will be inaccurate. Regular testing is essential.
• Sport Specificity: TSS was initially developed for power-based cycling. While adapted for running (using pace and grade), its direct application to other sports (e.g., strength training, swimming, team sports) is less straightforward and requires modified methods or different metrics. It doesn't fully capture the neurological or muscular stress of non-endurance activities.
• Subjective Feel: TSS is an objective measure, but it should always be combined with subjective feedback (Rate of Perceived Exertion - RPE, mood, sleep quality). Sometimes a low TSS workout can feel incredibly hard due to external factors, or a high TSS workout might feel manageable.

Applying TSS in Your Training

To effectively utilize TSS in your training, consider these steps:

• Establish Your Thresholds: Regularly test and update your Functional Threshold Power (FTP) for cycling or Functional Threshold Pace (rFTP) for running. This is the foundation for accurate TSS calculations.
• Use Training Software: Platforms like TrainingPeaks, Strava (with power meter data), or Garmin Connect automatically calculate TSS for your workouts and display your CTL, ATL, and TSB.
• Interpret Your Numbers: Don't just chase high TSS numbers. Understand what your daily, weekly, and monthly TSS totals mean in the context of your training goals.
  • Daily: What was the stress of this workout?
  • Weekly: Am I accumulating appropriate load for my phase of training? Am I recovering enough?
  • Monthly/Annual: Is my fitness (CTL) progressing? Am I managing my fatigue (ATL) and readiness (TSB) effectively for key events?
• Work with a Coach: An experienced coach can help you set appropriate TSS targets, interpret your data, and adjust your training plan based on your individual response to training stress.

Conclusion: TSS as a Cornerstone of Smart Training

The Training Stress Score (TSS) is a powerful, evidence-based metric that has revolutionized endurance training. By providing a quantifiable measure of training load, it empowers athletes and coaches to move beyond subjective feelings and make data-driven decisions about training intensity, duration, and recovery. While a 100 TSS workout represents a significant physiological challenge and serves as a benchmark for threshold effort, its true value lies in its ability to contribute to a holistic understanding of training stress. When used thoughtfully and in conjunction with other metrics and subjective feedback, TSS becomes a cornerstone of intelligent, progressive training that optimizes performance and minimizes the risk of overtraining.