Fatigue Level: Why Understanding Your Fatigue Level is the Key to Sustainable Training Success

What is the Fatigue Level?

Your fatigue level represents the ratio between your fitness and your fatigue. Specifically, your acute training load (the strain from recent training sessions) is divided by your chronic training load (your long-term average).

Simply put: This ratio indicates whether you are currently training more or less compared to your usual training level.

Explanation:

• Fitness: Refers to your overall performance level, influenced by long-term training load. Higher fitness values generally mean your body is better adapted to training and can handle greater loads.

• Fatigue: Describes the short-term impact of intense training sessions on your body. High fatigue levels can lead to reduced performance.

This ratio provides insight into your current training level in the context of fitness and fatigue. A high fatigue level relative to fitness suggests that you may be training at your limit. A lower value indicates that you are recovering well and training within your capacity.

Example:

If your chronic training load is around 120 on average, and you complete a training session today with a training load of 150, you are at the upper limit of your optimal training range.

150/130 = 1,15

However, this formula is simplified. To ensure that your current condition is assessed as accurately as possible, more recent training sessions are given more weight in the calculation. This is achieved by including the Exponentially Weighted Moving Average (EWMA). The EWMA is key in calculating fitness and fatigue by weighting past training data. More recent training sessions are given greater importance than older ones.

This means that the EWMA also influences the calculation of the fatigue level. Williams et al. (2017) examined why this approach is advantageous in more detail.

The Study:

They analyzed three different athlete profiles (Fig. 1), each with varying training loads but ultimately reaching the same fatigue level of 1.43, calculated using the moving average (EWMA).

Key takeaways:

• The EWMA reacts more quickly to significantly higher training loads (Athlete 1, 3).

• The EWMA is higher when training load steadily increases (Athlete 2).

• The EWMA adapts better during recovery phases (Athlete 2).

Fig. 1: EWMA vs. rolling average (Williams et al., 2017)

What Does a Value Between 0 and 2 Mean?

Your fatigue level, shown as a value between 0 and 2, indicates your body’s current load. The optimal range—the so-called “sweet spot”—lies between 0.8 and 1.3.

Fig. 2: Chronic & acute workload ratio (Windt & Gabbett, 2017)

• If your fatigue level is below 0.8, your body is in a very well-rested state. This means you’ve been training significantly less compared to previous weeks. While your fitness may decline slightly, your form improves to some extent. This scenario is common in tapering phases, off-season breaks, or after extended illness. Read more about the effects of longer training breaks in the blog post Detraining.

• If your fatigue level is between 0.8 and 1, you are in a light recovery phase. These phases are crucial because fitness cannot be continuously increased. Your body needs these breaks to recover and adapt to training stimuli. In the graph, this recovery phase is represented by the blue line.

• If your fatigue level is between 1 and 1.3, you are maintaining or even improving your fitness level. Your body is slightly fatigued but remains within the optimal zone for performance improvement.

• If your fatigue level is between 1.3 and 1.5, you may be overtraining. In Fig. 3, this is indicated by the yellow line. This can occur if a workout is longer or more intense than planned. You should not remain in this “overtraining” zone for too long, as the risk of overuse injuries increases!

• If your fatigue level exceeds 1.5, a rest day is necessary. In this case, you’ve done too much recently, and your body was not adequately prepared for the load. There are two main scenarios in which this can happen:

  • You are new to training and have little or inconsistent training history. This means Enduco does not yet have enough data to “know” you well. Enduco requires approximately three weeks to assess your training load and display an accurate fatigue level. In this case, simply monitor your training volume and avoid increasing it too rapidly.

  • You have completed a long and intense race. After such an event, your fatigue level may approach 1.5. However, Enduco’s goal is to optimally prepare you for races so that you can handle the load effectively.

Fig. 3: Fatigue level over 90 days in the Analytics tab

What is the Difference Between Fatigue Level and Fatigue?

The difference between fatigue level and fatigue lies in their meaning and calculation:

• Fatigue refers to your current load state and reflects the short-term strain from the past 7 days of training.

• Fatigue level, on the other hand, is a ratio comparing your fatigue to your fitness. It indicates how much strain your body is under in relation to your usual training level.