PEM discussion thread - post-exertional malaise

[poetinsf]

And mental exertion uses minimal calories – fewer than the type of physical activities which the same patients are able to do without causing PEM. So if PEM can be caused by mental exertion that would be evidence that it’s not caused by the use of calories.

Whatever the damage caused by that calorie expenditure is confined in the brain and they'll need to be cleaned up or repaired by the brain immune system. No reason to think that such repair process won't cause PEM.

 

[Jonathan Edwards]

In any case, the notion of exertion as a subjective concept, at least pertaining to PEM, needs to be dispatched with.

But if it is the basis of a symptom that patients are expected to recognise it has to be subjective. They do not measure calories. If you want to get away from that then presumably exertion should not be used as a term. We should talk of power (calories per time would be power) or of total energy usage. So far I don't think we have established even which of those is relevant - and they are very different in implications.

 

[Peter T]

Subjectively it feels that a simple measure like calories per unit of time does not correspond to what ever culminates in triggering PEM. Other things interact like the novelty of the activity, additional sensory stimuli or orthostatic issues. For example walking x metres on level ground alone, might not trigger PEM but walking x metres over uneven ground whilst talking to someone might. A subjective, in a non scientific sense, feeling of effort seems to relate to triggering PEM over and above what theoretically could be measured in joules.

Also units of whatever cumulates to trigger PEM, again subjectively, does not seem to have a simple relationship with time; for example walking a hundred metres in one go might trigger PEM, but walking ten metres ten times over a period of time might not. However doing different things, each alone does not trigger PEM, over a period of time may cumulatively trigger PEM. It is not obvious whether the relevant time period is hours or days, whether interspersing rest impacts the consequences of activity, what the impact of switching between types of activity (physical, cognitive, etc) is.

Also in relation to PEM, either pre triggering or when in ‘recovery’, what are the vital components of rest. Some years ago I experimented with the idea that periods of lying flat on my back in a darkened room with out any distraction, sound, etc and trying to empty my mind of any thoughts might enable me to increase productive activity in any time period. Although this may be a necessary response to PEM once triggered, I found trying to do this preemptively was anything but restful and messed up my psychological state, I found such preemptive rest required some form of distraction to be achievable, that is som low level cognitive activity made the rest more restful.

 

[Hutan]

I've mentioned elsewhere that adrenalin (which causes some downstream biochemical effects such as production of interferons) might be a mechanism that can explain why both physical and mental exertion can cause PEM. That would help to explain why 3 hours of mental work done while lying down in bed might not cause PEM, but the same amount of work done while upright and to a deadline might be more likely to.

Adrenalin seems to allow action now, at the cost of function later. A less pronounced version of that than PEM probably is a normal survival benefit for an animal - in an emergency you can perform, but you do need to rest after, to recover.

I've seen lots of people here say that they feel temporarily better when stressed or when there is something novel happening. Perhaps the adrenalin response to a stressor is operating normally, but it is that the release of interferons and whatever else as a result of the adrenalin is causing the problem?

 

[jnmaciuch]

I think there are a myriad of ways in which “exertion” could refer to a biological process that is not strictly correlated with “calories” (itself poorly defined in a biological context).

When it comes to energy consumption of the brain, it also bears remembering that the processes of substrate mobilization and utilization are going to be very different from the muscle.

Meaning that if PEM has something to do with the processes which increase utilization of different fuel sources (be that AMPK phosphorylation, increased glucose uptake, fatty acid mobilization, etc), this will look different between tissues.

For example, in the brain, the primary fuel source is lactate supplied dynamically by astrocytes which themselves uptake and process glucose. In the muscle, you have a combination of glucose usage and local fat stores, which release more fatty acids locally in response to activity.

So yes, it would be oversimplistic to talk only of calories for many reasons, least of which because modulation of cellular metabolism in the brain, and what may happen when those various processes operate less efficiently, looks massively different than in muscle (and looks different still than other tissues)

 

[jnmaciuch]

which causes some downstream biochemical effects such as production of interferons

Could you share the source for this? I’d be interested to read as I’ve only heard of the relationship going in the opposite direction

 

[Utsikt]

I think there are a myriad of ways in which “exertion” could refer to a biological process that is not strictly correlated with “calories” (itself poorly defined in a biological context).

I thought calorie was a unit of energy is very precisely defined (as most physics units are)?

 

[jnmaciuch]

I thought calorie was a unit of energy is very precisely defined (as most physics units are)?

and it can be measured at the level of direct chemical interactions very well.

In the biological context, where you have billions of interactions happening on top of each other with different thermogenic properties, along with systemic regulation of body temperature obscuring the ability to measure heat change, you can’t measure anything definitely.

All calorie estimates for food or activity at anything more complicated than a few in-vitro protein interactions are simply a guess based on numbers from some very controlled reactions that may not apply at all in a living organism