COROS Coaches: Fatigue Monitoring

As part of our COROS Coaches initiative, we recently received a question about Fatigue monitoring and its impact on training progression. Let’s take a dive into our analysis so you can benefit from our coaching insight and improve your own training journey!

The topic breakdown is followed by our full coaches’ analysis and feedback on the athlete’s question.

How to Monitor Fatigue

As we embark on a new year, you may have many new training resolutions and a massive amount of motivation to crush them all! However, following the excitement of new objectives may lead to some steps skipped. As you begin new training plans, it is important to closely monitor your progression and effort towards this new workload with advanced metrics at your disposal.

Fatigue is an important metric to look over as you train. You can think of fatigue as your body’s personal alarm. If it reaches a certain point, it will make sure to yell it out to you in painful ways. Unfortunately, the alarm often sets off when it’s too late, leading to injuries. Therefore, we recommend becoming familiar with our fatigue metric so you can adjust your training in time!

Sports Science Insight

Fatigue is your body’s response to exercise. During training, your body faces a significant amount of muscle breakdown and cardiac/pulmonary demand. The adaptation we are seeking happens during days off as your body builds back stronger. Accumulated fatigue is your body’s message that there is too much breakdown and requires recovery before your body experiences an injury.


An athlete with two years of running experience has recently started a new training plan in hopes to improve his running endurance. His Training Load Management Chart can be seen below. The new training plan started shortly before Christmas and we can see their Fatigue build from 45 to 85 in a short amount of time.

Training-Related Question

How can I keep following this new training plan without it leading to excessive fatigue?
Training Load Management Chart
Coaches’ Analysis

The Training Load Management chart remains the best tool in EvoLab to monitor overall fitness. We can clearly notice a steep increase in fatigue once the new training plan started. While this chart provides overall feedback, we need to seek additional information to find what is causing this sudden increase and determine if it puts the athlete at risk of injury. Below are the main graphs used to analyze the situation.

7-Day Total Training Load Chart

The athlete has a recent weekly average training load almost twice their recommended average based on historical data (~1500TL vs. ~850TL per week).

Weekly Average Training Load

The athlete has a completion rate of 185.7% which means they may be training more than what is originally planned.

Threshold Heart Rate Zones Distribution

The athlete spends most of their time (>90%) at low intensity. This confirms that intensity is being well handled.

Coaches’ feedback

Although there are appropriate times to reach high fatigue values, we recommend this athlete to decrease volume slightly to maintain fatigue between 40-60. In this specific situation, it is the ideal range for improving fitness while keeping a low risk of injury. The athlete can decrease mileage via two different ways:

  • Add one additional off-day per week by removing an easy run from the plan.
  • Reduce 10-20% of mileage per easy run.

As the body only remembers the last four weeks of training, the athlete should keep a weekly training load of 900-1000 over the first week or so of their new training plan to maintain a progressive overload. This will ensure that their body properly adapts to new stimulus and gets ready for higher intensities! It would become relevant down the road to ramp up intensity depending on the event and training stages.

Coaching Tip

As you begin a new training plan, make sure you have the required volume history. Aim for an increase of ~10% in weekly distance or training load based on your last 4 weeks.
Fatigue & 7-Day Total TL Chart

Shortly after our discussion, the athlete has adjusted their plan. We can notice Fatigue and Weekly TL metrics back to safe values!

If you would like your own training questions answered, head over to our COROS Coaches Blog for steps to submitting your questions!

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