Tag Archives: stress

There is no such thing as “it’s just stress.”

On a fundamental level, the body is put together in very simple ways. All the body’s incredible sophistication—its intricate neural circuits, circulatory, respiratory, and digestive plumbing, and hormonal signaling—is the result of increasingly complex layers of function added on top of basic logics.

And one of the most basic is stress.

Stress is the body being put into a position to face something that (correctly or incorrectly) it perceives it must cope with. Before the word stress was used to describe a physiological process, it was actually used in materials engineering to describe how different things interacted with their environment. The definition of stress in this primordial sense is “a force acting on a resistance.” Some examples:

The weight of a car resting on its suspension system.

A tree straining against a hurricane.

A football player attempting to break a tackle.

Stress by itself is not a bad thing. Just being awake equals more stress than being asleep. Walking equals more stress than sitting down. Any bit of movement or thinking that we do means more stress than not doing it.

A stressed state is different. This is a state is one where the level of stress has risen to a point that the body is putting so much effort into coping with something—it’s putting so much force on a particular resistance (or resistance on a particular force)—that it has to stop doing all kinds of things that it needs in order to stay alive over the long-term.

Pulling an all-nighter, for example.

If you stayed awake studying or working, and you did that long enough or often enough, you’d find yourself getting sicker. This is not because your body got too tired (which it probably did) but more specifically because it didn’t get the chance to recover. Why? Because pulling an all-nighter is far enough out of the body’s functional paradigm—a fancy way of saying “what it does well”—that it had to stop doing all the menial duties and basic upkeep that let it recover well.

Understanding what a stressed state is (and isn’t) is a matter of common sense: even though you can’t stay awake forever just lying in bed, being awake for 16 hours out of the day isn’t a “stressed state.” Why? Because the body is supposed to stay awake (more or less) for 16 hours, and sleep (more or less) for 8. So that pattern of activity allows it to keep recovering at the proper rate, maximizing its ability to stay alive.

So by that logic, you can begin to see how things that could solidly count as stressed states if taken by themselves can be OK when put into the right context. Staying awake for the right amount of time is just OK. But try to stay awake for a week and you’ll go nuts—or at least we can say that your job performance will drop rather dramatically.

You screw with that natural pattern of activity and then you go into a stressed state.

Let’s look at more sporty stuff: sprints. There is simply no way that the body can sustain a sprint for any period of time that even looks like long-term. Just 10 seconds of sustained maximal intensity effort creates a huge amount of anaerobic debt. Attempting to sustain such an effort for a significant period of time would pose an existential challenge to the body’s integrity.

A sprint requires complete shutdown of the processes that keep the body alive in the long-term. Recycling of cerebrospinal fluid, muscle repair, digestion, replacement of red and white blood cells, and sometimes even breathing—it all stops. That’s perfectly OK, or course, because a sprint is expected to stop within 10-20 seconds, and all those processes have a chance to restart again.

But if they don’t—if, for better or worse, the body insistently perceives that the intensity, frequency, or volume of training and racing is threatening to its physical integrity—then it never gets the chance to rest and recover.

All the touted health benefits of HIT—the development of more muscle and bone mass, stimulation of mitochondria, etc.—never get to happen. All that development is a response to the massive tissue breakdown that occurs in high-intensity training. This means that it comes after. If the body perceives that the period of high demand keeps going, it’s going to keep waiting for the right time to build itself back up.

That’s just fine if you train conservatively (read: infrequently enough that your body can rest, and recover, and grow from whatever training it is that you do). But just because a certain kind of training has theoretical benefits doesn’t mean your body can reap those benefits under all conditions.

If the acute stress doesn’t wane, all those critical recovery processes simply won’t restart (or won’t be working well enough to really make a difference—take your pick).

The point is that this is the case with all stressed states. Regardless of why it happens, whenever your body perceives that there is some kind of present threat, a bunch of critical processes are going to stop. (And if some of them are designed to keep other critical processes in check, they’re going to go awry.)

So, if you’re stressed out, and you get sick, it’s far from “just stress.” What it means is that your immune system either shut down (and you got an infection) or it went nuts (and you got a cold) because your body shut down a bunch of systems in order to focus on a clear and present threat to its existence (real or perceived).

If this keeps going for a significant amount of time, your body’s going to start coming apart at the seams.

It’s almost impossible to do an “easy workout” when you’re stressed.

A while ago I read an excellent article titled Why heart rate always matters. It goes into great detail on a topic I’ve previously discussed here on running in systems: why the heart rate is always going to be an excellent representation of what is happening with the body’s stress response and energy metabolism. I think that some of the topics it discusses, as well as the excellent debate in the comments, are worth expanding on. Here’s an excerpt from it:

“Our fight-or-flight system often activates without any actual demand. When we get ‘stressed out’–engaged in a heated argument, mulling over a burdensome worry, or simply sitting in traffic–seldom is any physical task being undertaken. But the body is being activated. The engine is revving higher and tremendous sugar–the preferred fuel of fight-or-flight responses–is burned when under psychological stress, which is a major factor in ‘stress eating!’ We function as if we’re fighting an intense battle.

Stressed out and going for a run? Your body will perceive the cost of that run as higher (because it is already dealing with your life stress) and will activate a more intense energy system to cover all the demands. More energy cost!”

There was a particular comment in the article that I wanted to address:

“Very well written article and I agree with most of it.
However, I think you overstate the impact of activation level on energy expenditure…

…In my understanding, the energy demand dictates the energy production. And the energy demand is mainly dictated by the mechanical work of the muscles and all the side processes needed for that level of power output.
I agree, that the excitation level directly impacts the chosen energy supply system but as long as this system doesn’t actively provide energy, it’s [maintaining] cost will be relatively low.
Yes, a higher activation will have a higher energy demand but I don’t believe it’ll come anywhere close to exceeded mechanical [energy] demands.”

I agree with the commenter in that I, also, believe that the author was overstating the impact of activation level on energy expenditure. However, I think the author’s overstatement makes it difficult to observe 2 key implications of this discussion:

  1. Activation level  (a.k.a. stress) changes the type of energy metabolism, which means that it changes the ratios of fuel (fat and sugar) that it uses.
  2. Training stimulus is inextricably tied to activation level and energy metabolism. This means that the ratios of fuel usage have a much bigger say in how the body perceives the workout (as low-intensity vs. high-intensity) than the rates of fuel usage.

The point is that while the author does overstate the energy cost of the stressors he mentions, it doesn’t really matter—there’s things the athlete just can’t get out of training if their body is taxed in the ways the article mentions.

A lot of people think that low-intensity means “slow,” “easy,” or “consuming little energy.” It doesn’t. Low-intensity is when the workout is easy on the body—specifically, when the body is burning a majority of fats for fuel, and the sugar that is being utilized is burned wholly aerobically  (in the presence of oxygen). In other words, there is no substantive anaerobic work. Highly-trained endurance athletes, who burn fats at much greater rates than the rest of us, can run at very high speeds while remaining in a completely aerobic state. Such an athlete may be running blazing times in a workout that is for them, metabolically speaking, a low-intensity workout.

Now let’s look at higher intensities: In order to produce the energy necessary to approach your top speed, a lot of changes have to happen within the body. One of these is that the body has to go from burning a greater percentage of fats (which burn relatively slowly and so provide energy at a relatively lower rate), to burning a greater percentage of sugars (which burn relatively more quickly and so provide energy at a much faster rate). So, in order to get closer to your top speed, a greater percentage of your energy has to come from sugar.

In order to release more sugar to the bloodstream (to be utilized by the muscles), the body releases hormones called glucocorticoids—glucose (a.k.a sugar) releasing hormones. The main glucocorticoid is cortisol, which many will recognize as the main stress hormone. Another hormone that is release during the stress response is insulin, which helps muscle cells avail themselves on the sugar that cortisol released into the bloodstream. Cortisol and insulin, then, work synergistically to produce (and increase) sugar metabolism.

To recap: want to run closer to your top speed? You need to release more sugar. How do you do that? By getting more stressed. But because of some of the body’s more complex molecular mechanics—fodder for another post—the body can’t release a bunch of sugar and still be releasing fats. What would happen is that you’d just flood the bloodstream with unhealthy concentrations of both fuels. So, when insulin is released or when anaerobic function (which is dependent on sugar) increases, fat-burning drops. If sugar-burning goes up, fat-burning goes down (and vice versa).

This works the other way around too. If you get more stressed because, say, you had a rough day at work, or you got into an argument, you’ve got more cortisol and insulin running through your body. But it’s not like the body can decide to release (and use) sugar only when the reason for cortisol and insulin release is because of increased athletic demand (a.k.a. athletic stress). For any other stress (work stress, etc.), cortisol and insulin become released, and increase carbohydrate metabolism. Research on the metabolic effects of social stress in fish supports this idea.

This, incidentally, is why people get tired after a stressful day at work or an argument that stretches for too long. They didn’t use up all their fat-stores at work, obviously. But because the stress put them in sugar-burning gear, enough of their sugar ran out that they start feeling tired. It’s not that they ran out of fuel, but rather that they ran out of the fuel they’ve been stuck using.

It also takes a relatively long time for the cortisol to get out of your system—and when it does, it’s not like you can just pop back into action and go for a run. The adrenal glands, which put out cortisol (not to mention various other mediators of the stress response) have been used up. They’re tired, and will resist further activity. And since you use all the glands in the body to one (significant) degree or another during training, it’s not a good idea to train with exhausted or depleted glands.

Asking your body to work out when you’re already out of a major fuel and your stress glands are tired is an even worse idea: the “same” workout is relatively much harder for a tired gland that’s nearly out of adrenaline and cortisol than for a rested gland. Training after a period of stress is, in physiological terms, almost exactly like doing back-to-back training sessions. Effectively, you’re extending the period of stress.

And if on top of that, your blood sugar is low (as usually happens after a period of stress), you’ll be asking those tired glands to produce even more cortisol and adrenaline than they would usually have to: in their already tired state, it’s not enough to simply produce enough cortisol to maintain blood sugar levels—they have to make up for the lack of sugar in the bloodstream.

If on top of that, you’re “stuck” in sugar-burning mode because you still have all that errant cortisol and insulin flowing through your system (since you’re still stressed), you’ll be depending on sugar—which you’ve substantively burned through—for the duration of your training session. Because the body is inhibited from fueling itself with fats (due to the insulin in your system), it has to rev up those exhausted adrenals even more to provide the requisite cortisol.

Insofar as your body is stressed, it will respond to what is normally an “easy” workout as if it were a “mini high-intensity workout.” In other words, you can’t really have a “low-intensity training session” when you’re stressed (and expect to accomplish your goals in any sort of way). 

This is why doing MAF training—exercising under the aerobic threshold—under stress (or after a period of stress) produces such a dramatic drop in speed/power output at the same heart rate. When you’re under stress, exercising at a rate that looks anything like the aerobic training you do when unstressed would mean elevating your heart rate far beyond your aerobic threshold. Because aerobic work output is so reduced in a stressed state, it’s a much better idea—and a much simpler fix to the problem—to simply rest for the day and do your “easy” training session tomorrow.

The Tales of Forgotten Subsystems, part III: aerobic respiration, a.k.a The Krebs Cycle.

What if I told you that by running at a lower intensity, you could boost your running efficiency by 600%?

You’d think I was lying.

Well, I’m not. That’s exactly what happens when we run at the right intensity. When we’re burning sugars anaerobically, the sugar only gets partially processed by the cell, and out comes lactate. But when we burn them aerobically, that lactate goes through another process: The Krebs Cycle.

Continue reading The Tales of Forgotten Subsystems, part III: aerobic respiration, a.k.a The Krebs Cycle.

4-count breathing: An exercise for runners, meditators, commandos, and everyone else.

4-count breathing is well-known as a relaxing exercise, a form of meditation, and a tactical combat tool. This is a very useful tool for runners, because it helps the body function aerobically at a very high level of performance. For those who don’t know what I’m referring to, 4-count breathing is a technique that consists of the following steps:


Continue reading 4-count breathing: An exercise for runners, meditators, commandos, and everyone else.