Training Stress Score (TSS): The Key Metric Every Endurance Athlete Should Understand

If you’re serious about improving your endurance performance, there’s one training metric that stands above the rest in importance: Training Stress Score (TSS). This powerful number can transform how you train, recover, and perform when it matters most. Now if you are lucky and working with a coach (like me) they will already be analysing and using this data. However, for those riding solo, or just interested in learning what goes on behind the curtain, let’s dive into what TSS is and why understanding it could be your key to better results.

What Exactly Is Training Stress Score?

Training Stress Score (TSS) is a numerical value that captures both the intensity and duration of your workout in a single, easy-to-understand number. Developed by Dr. Andrew Coggan and Hunter Allen for cycling training, the concept has since expanded to running, swimming, and other endurance disciplines.

At its core, TSS represents how much strain you’ve put on your body during a workout compared to what you could sustain for an hour at your maximum sustainable effort. The calculation takes into account your workout duration, normalized power (or equivalent metric for your sport), and intensity factor relative to your functional threshold power (FTP) or threshold pace.

For reference, an all-out one-hour effort at your threshold would give you a TSS of 100. A gentle recovery session might score 30-40, while a brutal three-hour race could rack up 250+ points. This standardization makes TSS incredibly valuable for comparing different types of workouts and tracking your training over time.

Why TSS Matters for Your Performance

Training without tracking TSS is like managing your finances without looking at your bank account. Sure, you might be able to get by on feel, but you’re missing crucial information that could help you make better decisions.

Objective Measurement of Training Load

Even the most experienced athletes can misjudge workout intensity. One day, a moderate effort might feel easy because you’re well-rested; the next day, that same workout might feel brutally hard because you’re tired, stressed, or didn’t fuel properly.

TSS cuts through the subjective experience and tells you exactly how much work your body performed. This objectivity becomes invaluable when planning training progressions and recovery periods.

Preventing the Overtraining Trap

The path to improved endurance performance involves pushing your limits—but push too far, too often, and you’ll find yourself injured, burnt out, or watching your performance plateau.

By monitoring your weekly TSS totals, you can ensure you’re training hard enough to stimulate adaptation without crossing into dangerous territory. Experienced coaches typically recommend different weekly TSS ranges based on your goals and experience level:

Recreational athletes pursuing general fitness might aim for 300-450 TSS per week, while serious amateurs training for competitions might target 450-700. Elite athletes can handle 700-1000+ TSS weekly, but they’ve built up to these levels progressively over years.

More importantly, TSS helps you avoid sudden increases in training load—often the primary culprit behind overuse injuries. The general guideline is to limit weekly TSS increases to 10-15% at most.

Precision-Guided Periodization

All effective training plans incorporate some form of periodization—alternating between building fitness and recovering—but TSS makes this process much more precise.

Instead of vaguely planning “hard weeks” and “easy weeks,” you can set specific TSS targets. A common approach is the 3:1 model: three weeks gradually increasing TSS followed by one week at 60-70% of your highest week’s load. This structure provides enough stress to stimulate adaptation and enough recovery to absorb the benefits.

Tracking Fitness and Fatigue

TSS contributes to two critical training metrics that help forecast your performance:

Chronic Training Load (CTL) represents your fitness level, calculated as the average daily TSS over the past six weeks. As this number rises, so does your capacity for endurance work.

Acute Training Load (ATL) indicates your fatigue level, based on average daily TSS over the past week. This number increases rapidly when you train hard and drops when you rest.

The difference between CTL and ATL gives you your Training Stress Balance (TSB), which predicts your race readiness. A positive TSB suggests freshness, while a negative number indicates fatigue.

Strategic Race Preparation

Perhaps the most practical application of TSS is in tapering for important events. Most athletes perform best when they reach the starting line with a TSB between +5 and +25, indicating they’ve reduced fatigue while maintaining fitness.

By managing your TSS in the weeks leading up to competition, you can hit this optimal range with precision rather than guessing at how much to cut back. This approach helps eliminate the common race day problems of feeling flat (overtapered) or tired (undertapered).

Making TSS Work For Your Training

Understanding the concept of TSS is just the beginning. Here’s how to implement it effectively in your training:

Establish Accurate Baseline Values

Before TSS can provide meaningful data, you need accurate baseline measurements for your current fitness. For cyclists, this means determining your Functional Threshold Power through testing. Runners will need their threshold pace or power, while swimmers should establish their threshold pace.

These values change as your fitness improves, so plan to reassess every 4-8 weeks during focused training blocks.

Focus on Weekly Patterns, Not Daily Numbers

While it’s tempting to analyze each workout’s TSS in isolation, the more important metric is your weekly total. This broader view helps you maintain perspective and avoid the trap of making every workout “special.”

Successful athletes typically follow patterns where training load increases gradually for 3-4 weeks, then drops for a recovery week before building again. This approach allows for consistent progress without overreaching.

Create Meaningful Contrasts Between Workouts

The most effective training plans include clear distinctions between hard and easy days. When viewing your training through the lens of TSS, this means some workouts should generate high TSS values while others should deliberately aim for lower numbers.

A well-structured week might include one or two high-TSS key sessions that push your limits, several moderate maintenance workouts, and two or three low-TSS recovery sessions. This variance allows your body to absorb the stress of hard training through adequate recovery.

Consider Intensity Distribution

Two workouts with identical TSS values can affect your body in dramatically different ways. A four-hour easy ride might generate the same TSS as a 45-minute high-intensity interval session, but they stress different energy systems and require different recovery strategies.

For optimal development, most endurance athletes need a mix of both approaches: long, steady efforts to build aerobic capacity and shorter, intense sessions to improve power and speed. TSS helps you quantify both types of stress, but you’ll still need to consider the nature of each workout when planning your training.

Understanding the Limitations

As valuable as TSS is, it’s not a perfect measurement of all training stress:

TSS doesn’t fully account for environmental factors like heat, humidity, or altitude, all of which can significantly increase the physiological cost of training. A 100-TSS workout in 95-degree heat is much more demanding than the same workout in comfortable conditions.

It also doesn’t distinguish between different types of physiological stress. A workout heavy on anaerobic efforts might generate the same TSS as a purely aerobic session but could require much more recovery time.

Perhaps most importantly, TSS only measures training stress, not life stress. Sleep quality, work pressure, family responsibilities, and countless other factors influence your ability to recover from training.

Use TSS as a powerful guiding tool, but combine it with subjective measures like perceived exertion and recovery quality for a complete picture of your training status.

Putting It All Together

Training Stress Score gives you an objective way to quantify, track, and plan your endurance training. By monitoring this metric over time, you can train more effectively, recover more strategically, and perform better when it matters most.

Most importantly, TSS helps you avoid the two most common training mistakes: doing too much too soon and failing to recover adequately between hard efforts. Whether you’re preparing for your first century ride or your tenth marathon, understanding and applying TSS principles can help you train smarter, not just harder.

In endurance sports, where consistent training over months and years leads to success, tools that help you sustain your efforts without breakdown are invaluable. TSS might just be the most important number you’re not yet tracking.

Are you using TSS to guide your training? Share your experience in the comments below, or reach out if you need help implementing this powerful metric into your training plan.