Training Stress Score (TSS) is a metric designed to quantify the difficulty of a training session and the cumulative load over time. Used by platforms like TrainingPeaks, Strava, Garmin, and Wahoo, TSS helps cyclists and endurance athletes monitor and plan their training. However, while TSS is a valuable tool, it’s important to understand its limitations and how it fits into a broader training strategy.

What Is TSS and How Is It Calculated?

TSS is most commonly associated with TrainingPeaks, but similar systems are used across other training platforms. The calculation is based on your Functional Threshold Power (FTP)—the maximum effort you can sustain for an hour. If you ride at your FTP for 60 minutes, you’ll score 100 TSS for that session. The formula considers the ratio of your normalized power to your threshold power, multiplied by ride duration. While the exact coefficients may vary between platforms, the principle remains: 100 TSS in 60 minutes represents a maximal effort.

It’s worth noting that TSS for running and swimming is calculated similarly, but this article focuses on cycling.

Is More TSS Always Better?

Once you know how to calculate TSS, the next question is: what should you aim for? The answer is as much as is sustainable. Training is about applying stress and allowing your body to adapt. However, TSS alone doesn’t capture the full picture. For example, two training weeks with similar TSS values can have very different impacts depending on the distribution of intensity and recovery.

The week above includes two hard interval sessions and totals 620 TSS. The week below has one hard session and 576 TSS.

Although the TSS difference is only 7%, the top week is much harder and less sustainable. Research suggests that using intensity sparingly and focusing on effective distribution leads to better long-term results. TSS does not account for the sustainability of your training or the context of each session.

Pros and Cons of Using TSS to Measure Training Load

Pros:

• Simple way to gauge the difficulty of a session
• Helps with planning and tracking training over time

Cons:

• Does not consider the order of sessions or accumulated fatigue
• Fails to reflect how hard a session feels depending on what came before
• May not accurately represent the stress of intervals placed at different points in a ride

For example, doing intervals at the end of a long ride is much harder than at the start, but TSS may not reflect this difference.

Alternative Ways to Measure Training Load

Another approach is to track hours spent in different intensity zones. For many cyclists, “hard” means anything above zone two or above the first lactate threshold. For a rider with an FTP of 400W, this might mean any riding over 300W. While this method also has limitations, it can provide a clearer picture of your training week, especially when considering aerobic versus high-intensity work.

If you’re looking for ways to improve your cycling performance without simply increasing your training load, you might find our article on how to get faster without training helpful. It explores practical strategies that complement structured training and can work alongside metrics like TSS.

Key Takeaways

TSS is a useful metric for cyclists, offering a quick reference for session difficulty and overall load. However, it’s not perfect and should be used alongside other measures. Keeping training simple—focusing on aerobic volume with a small proportion of intensity (no more than 20% of total volume)—is often the most effective approach.

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