What Is Ergodicity?

Ice baths for recovery

I did not know what the word 'ergodicity' meant. I had to look it up. It means when you do a test or research on a whole group, you assume the result applies to everyone. Say you get a hundred gorrillas to flip a coin 10 times. All 10 flips ends up with a head. You then conclude that all gorillas can always flip 10 heads in a row with 10 coin flips.

Can you see the error with this conclusion? Neumann and colleagues (2021), sugests that sports scientists may inadvertently be making errors like this frequently. Their research studied the relationship between training load and recovery. If you're into endurance sports, you know recovery is really crucial.

When you train more, your fitness improves, however, it also increases your chances of injury and burnout. This has led to all sorts of research to investigate how we handle different training loads and how quickly we recover so that we can train harder without breaking down.

So, is there a link between training load and recovery? Is it possible to measure training load and subsequent recovery in a large group of people and use those results to recommend or predict how you and I or any individual would respond?

Neumann and colleagues (2020) studied footballers from a top Dutch football league club, over 2 seasons. Daily training and recovery data were collected from footballers of their under-17, under-19 and under-23 teams.

The most basic question to address is if total training load in a workout affect how recovered the footballers feel before the next day's training session? This is done in 2 ways. 

For the whole group analysis, an average training load is calculated on a given day. The analysis is repeated for each workout day and you can average the results.

For each individual analysis, you monitor every pair of workout/ recovery scores for each individual over the course of the data. This data is then averaged. 

If both group and individual data produce identical results, then the training and recovery is ergodic, meaning the results of the group studies can be applied to individuals (like you and I). If results aren't identical then oops.....

Well, sure enough, the group and individual analyses produced different results. The correlations between training load and recovery did not match up. training loads varied far more for a given individual footballer over time than they did between individual footballers on a given day. How a bunch of people respond to a single workout session does not always tell how you respond to a series of workouts. 

I recall when running cross country in secondary school how all of us in the school team were given the same workout session and each of us responded differently.

You must be wondering now if all the previous research done on training and  on large groups apply to you, or whether they are invalid. Researchers use randomized placebo controlled trials to normalise the effects of individual variation. They also report individual results to group averages. 

Read and understand the recommendations from researchers to improve your personal training/ performance and recovery. But bear in mind that we are all an experiment of one (or n = 1). Age is also a confounder. What hurts now after a certain workout did not hurt when I was 28.

Reference

Neumann ND, Yperen NWV, Brauers JJ et al (2021). Nonergodicity In Load And Recovery: Group Results Do Not Generalize To Individuals. Int J Sp Physiol Perform. 17(3): 391-399. DOI: 10.1123/ijspp.2021-0126