Does arduous exercise compromise immunity?

Originally published at Uphill Athlete in July 2020.

A recent article solicited opposing expert arguments about exercise and immunity. The researchers wanted to know whether “arduous exercise” compromises immune function. But for practicing athletes, the answer doesn’t matter. And it could be detrimental to know for sure.

The important thing to realize is that training stress is only one stressor among many, and for non-professional athletes, it’s the one stressor that the athlete has complete control over.

Athlete immunity is about more than training

Imagine that you’re playing a game of Jenga. You pull away the plastic pile guide. One by one, you pull out blocks and stack them on top. At some point, the tower falls. When it does, which block is responsible? The top one, right?

No, not really. The position of every block contributes to the instability of the tower. The last block was just the last straw.

Blaming the last block is a case of the single-factor fallacy. We give one cause among many all the credit for the outcome.

Although the researchers acknowledge that “a key point of agreement between the [Yes/No] groups is that infection susceptibility has a multifactorial underpinning”, they’re still curious if training on its own can compromise immunity. For active athletes, the eventual conclusion is irrelevant and possibly dangerous.

Stress comes from many factors

When I started structured endurance training, I used the strong-like-bull-smart-like-tractor approach. I had a full life, and I tried to cram a heavy training load into the space remaining. Unfortunately, I was stupider than I was strong. I ended up getting sick a lot more than usual.

The frequency was enough for my friends and family to comment. Eventually, I cracked the code, but my sick episodes created a permanent impression. “You always get sick,” a friend said, even after I had been healthy for over a year.

By blaming the training, my friends and family were guilty of the single-factor fallacy. They accepted non-training life stressors as given, labeled training as the optional add-on, and then assigned the blame to it.

For most people, training is an optional add-on. But like a game of Jenga, training was just the top block in the pile. I would have much rather dialed back my life stress than dialed back my training. But I didn’t do either, so I got sick.

The reality is that all my life stress contributed to those first few years. And at least twice a year the baseline factors were significant and pushed me over the edge. But eventually, I wised up. I decreased my baseline stress, and I was able to increase my training volume by 40%. In that same year, I stayed healthy for 425 days and had my best performances ever.

Stay healthy by managing your stress

So rather than blame one factor, ask yourself some hard questions:

  1. What margin of safety do I need to deal with the unexpected and still stay healthy?
  2. With that margin of safety, do I have enough remaining bandwidth for the training I need to reach my goals?
  3. If not, can I decrease my baseline stress? and
  4. Can I increase my breaking point? or
  5. Should I accept the bandwidth that I have available and dial back my training instead?

1. What margin of safety do you need to stay healthy?

At best, training is fudgy and imprecise, so it’s silly to try and come up with an exact margin of safety. Instead, what works well is to never go to your limits in training. (But racing is another story.) HIIT aficionados will hate the thought of delayed gratification, but it’s much more sustainable in the long-term.

To do so, always have one more hour or one more interval left in the tank. Do as much as necessary, not as much as possible. Otherwise, you’re grinding yourself down. You’ll get weaker over time and, eventually, sick.

2. Do you have enough bandwidth available?

There’s a reason that many pro athletes live like monks. The fewer external stressors they have, the more time and energy they can devote to training. In contrast, the strong-like-bull-smart-like-tractor approach tries to cram everything in, acting as if trees can grow to the sky.

The former is performance-driven and says no to anything that doesn’t contribute. The latter is gratification-driven and says yes to anything and everything.

If we have responsibilities that aren’t important, we need to get rid of them. If they are important, we have to accept them and work around them, not fool ourselves and get greedy.

Our total bandwidth is what’s between our baseline and our breaking point. Our baseline is the number of inescapable demands on us. Our breaking point is our mental and physical limits.

3. Can you decrease your baseline stress?

I think of baseline stress as anything external, primarily work, people, and travel.

Can you work less? Or in a less-demanding job? Can you spend less time with stressful people? Can you avoid non-training travel?

4. Can you increase your breaking point?

While I think of baseline stress as external, resilience and vulnerability are internal. So what can we do to decrease vulnerability?

The primary factors are food, sleep, and attitude.

  • Are you eating well? Is your diet nutritious and free of processed food and alcohol?
  • Do you sleep at least eight hours per night? Can you take a nap in the afternoon?
  • Can you improve your attitude in a practical way? Can you let go of what you can’t control?

But what defines "arduous exercise"?

The article defines arduous exercise as “those activities practiced by high-performance athletes [and]military personnel that greatly exceed recommended physical activity guidelines”. But that’s a little vague.

A training session that might barely qualify as a recovery day for someone like Kilian Jornet might so severely tax a less well-trained athlete that it would leave that person broken.

So saying that a training load of X is hazardous is non-specific and silly. It depends on the work capacity of the athlete and what “arduous” training they are used to.

And why doesn't the effect on immunity matter?

But even more importantly, whether arduous activity compromises immunity doesn’t matter. And, worse, it would be dangerous to know if it didn’t. If it were somehow proven that training had no effect on immunity, athletes would look at it in isolation. It would be “a get out of jail free card”. They would overtrain.

Only by looking at every factor can an athlete get a good idea of how much they can handle. And then, with the right dose of humility, they can marshal their resources according to their capacity and priorities.