How to Work with Your Fatigue Threshold

I wrote last week about the benefit of rest-based interval workouts and briefly touched on the fatigue threshold. This week is all about understanding what this threshold is and how it can help you improve your performance.

Your fatigue threshold is simply the point in a workout or race at which the body begins to experience a decline in performance. Here are two examples of how and why this happens, and how you can use your own fatigue threshold to your advantage.

Jeff ran his first 22 kilometre training run in preparation for a marathon. Up until this run, he had covered 19 kilometres in his training. He ran at the planned effort level—easy and conversational—and felt strong up to about 21 kilometres, when he began to feel more fatigued. His legs stiffened and his effort level increased even though he was running at a constant pace.

These are the signs that he crossed his fatigue threshold as it became more difficult to hold his pace, form, and effort. The goal of training is to push hard, maintain form, and reach or just exceed this threshold. Had he continued on for more than another kilometre, his performance would have begun to decline at a more rapid rate. (Interestingly, you can also see his heart rate gradually increase, even though his pace and effort are steady and the terrain is level. This response is called cardiac creep and you can learn more about it in this post.)

It’s important to know the signs that indicate you’ve reached your threshold, because when we push too much beyond our running fitness level, it can create greater consequences with longer recovery times, increased risk of injuries from muscle fatigue, and poor form. I see this quite frequently with runners who are trying to catch up after a setback or meet a long-run mileage quota. Although finishing might look good in your training log, pushing too hard decreases the quality of your training, performance, and recovery rates.


The fatigue threshold informs you on where your body is in terms of performance, and just how much further you should carry on. It’s a little like your body is waving the white flag, telling you to be mindful that it has reached the point of fatigue and to avoid pushing a lot further. It’s also the point where it’s key to tune in and pay attention to form and any other hints your body is giving you that it has had enough for the day (muscle twinges, soreness, overall feeling of tiredness).

How to Use This Knowledge to Improve Performance

The fun part is tracking your fatigue threshold to use it to better tailor the progression rate of your workouts. For instance, when Jeff ran his 25 kilometre long run two weeks later, his threshold shifted up to the 24 kilometre point. He was able to hold good, solid form and effort beyond his former threshold because his body had recovered and adapted to the training.

Tracking your fatigue threshold allows you to see where you are, how you’ve progressed, and the rate at which your body adapts to the demands of training. It also helps you realise when you’re having a rough workout (when you hit your threshold early due to lack of training or illness) or a breakthrough workout (when your body adapts and gets stronger).

Keeping tabs on your fatigue threshold isn’t hard. All you need to do is tune into how you feel midrun (via perceived effort and/or heart rate) and keep track of this in your log or a spreadsheet. Ultimately, this information allows you to customise your training, make the most of every workout, and stay off the injured list.

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