075 Why We Stop

Vital with Paul Weber

Why We Stop: Hypotheses about Fatigue Mechanisms in CrossFit

Option A: Neural Drive + Disruption of Muscle Metabolic Homeostasis + Breathing Frequency + Heat + Heart Rate + Muscle Deoxygenation = Perception of Effort = Decision to Slow Down or Stop

Option B: Muscle force cannot meet the demand

Some combination of these two fatigue mechanisms, we suspect, explains exhaustion CrossFit.

The questions are: to what extent is each limiting me in this workout? And what do I do about it?

Hypothesis: above 40-50% of 1RM, you may be limited by muscle fatigue directly.

You can be not fatigued at all, completely fresh, but if I put 200% of your max clean on the bar and tell you to clean it, you won’t be able to clean it.

Even with low fatigue and maximal motivation.

That is a failure of the muscle to produce the necessary force.

Hypothesis: your perception of effort influences your decisions between work bouts.

First, we need to define perception of effort.

It’s the combination of neural drive, breathing frequency, heat, deoxygenation of the muscle, disruption of metabolic homeostasis, when these are occurring simultaneously, we perceive this as effort.

Once we surpass our tolerable amount of perceived effort, we slow down or stop.

In the lab and in training, this decision usually occurs prior to an imposed physiological limit.

In competition, motivation across all competitors is generally very high, and the gap between when you decide to slow down and when you have to slow down likely diminishes (still at play, but less pronounced).

What do I do about perception of effort?

You can train, so that you can hold faster paces with less perception of effort.

You can use affirmations, which lower your perception of effort.

You can reduce stress. Mental fatigue increases perception of effort which reduces work capacity.

You can slow down your breathing rate.

You can commit to a series of metrics.

Orienting on performance makes the reward immediate.

This is why I like to:
1. Measure everything
2. Include specific challenges to my clients on each training piece.

I use the language “I challenge you to get 9 rounds.”

This connects them to a performance metric that they believe is meaningful, increases their motivation and then gives them the immediate reward after having met the standard.

Conclusion

If you are consistently encountering loads above 40-50% of 1RM, then getting stronger is going to lower the % of 1RM and make the direct muscular fatigue mechanism less likely to limit you.

If you are in a workout with more of an endurance feel, then train and use the strategies I mentioned before to lower your perception of effort and go faster.

Further reading:
How Bad Do You Want It? By Matt Fitzgerald
Endure by Alex Hutchinson
Research of Dr. Samuele Marcora

Fatigue is specific to working muscles: no cross-over with single-leg cycling in trained cyclists

https://pubmed.ncbi.nlm.nih.gov/22806085/