Physical Activity Effects on Muscle Fatigue in Sport in Active Adults with Long COVID-19: An Observational Study 2023, Coscia et al.

An Italian study

It's not quite as much of a statement of the obvious and misplaced causation beliefs as it appears. They had 4 groups of young adults: competitive athletes (AA); sporty amateurs (MA); ski instructors (SI) and sedentary people (SP). They had all visited the sports medicine clinic and done a CPET in the year prior to getting Covid. They then did a CPET at 6 months after resolution of the acute disease, and assessments of fatigue and other things at 12 months.

The main story is that the people who had been active prior to getting Covid and were fatigued at 6 months had higher rates of a major reduction in fatigue, compared to the sedentary group, at the 12 month mark.


There's still quite a lot to say, and criticise, about the study, but it isn't as it appeared from the abstract.

 

First off, there was a selection bias in who participated in the study. There was a pool of around 6000 young adults, but they recruited only 506. Think about the young competitive athlete (mostly snow sports), probably training as part of a team. The people who had not regained their fitness after six months had probably left the mountains and gone home to mum and dad for the summer and stayed there. The same goes for the ski instructors and, perhaps to a lesser extent, the sporty amateurs who might have been working in hospitality in the mountain resort and enjoying the snow sports during their time off. The sedentary people would have been more likely to be able to keep working and living in the area, even with fatigue.

We don't know why people first visited the sports clinic and were given a CPET - perhaps some people who were very active at that point became sedentary. It's not clear when the categorisation was done. So, if a ski instructor came in to the clinic for investigation, and developed a fatiguing illness and gave up work, and then had Covid, would they have been categorised in the study as a ski instructor or a sedentary person? If a ski instructor had Covid and then had given up work by the 6 month mark, would they still be in the ski instructor group?

Although participants couldn't be taking any of a number of drugs, it's not clear if pre-existing fatigue or other symptoms were excluded.

It's also not clear what level of activity was maintained after the acute Covid infection. And that's a pretty important gap in this paper, given that they at times seem to be suggesting that it's not just the fitness level at the time of the Covid illness, but some maintenance of physical activity in the year after that has influenced outcomes at the 12 month mark.

 

That last sentence fully deserves ridicule. People had to measure their fatigue on a scale from 1 to 10. How can a decision about how to measure fatigue possibly support a hypothesis that fatigue is a global perceptual phenomenon? There is no logic.

A subjective scale like that has problems in terms of consistency over time, and between people. Edit to add - people who are often very active may notice even a slight reduction on performance and rate it highly. Therefore, together with the selection bias, that probably reduced the number of severely affected athletes, it's likely that the participants in the active groups had, on average, a narrower range of fatigue. So, a 7 from an athlete might have been more like a 4 for a sedentary person, whose life would not be so affected by a reduction in stamina. The impact of all that is that the active groups probably had more people only very mildly affected, and who were therefore more likely to get better.

 

They excluded people who were unable to score 75% of the maximum score - because they could not highlight the presence of mild cognitive alterations. So, potentially they excluded people with moderate and severe cognitive alterations. Was it to eliminate people who were either too stupid or too bad at the Italian language, so that there was some potential for their scores to increase as they regained their health? It's hard to know how impactful this decision was. The results should have been reported.

 

That's how they defined ME/CFS-like symptoms - fatigue (or muscle fatigue? it isn't clear) symptoms greater than a 5 on the 1 to 10 scale; mild but not major impairment of cognitive processes and lack of restorative sleep. Around 7% of their sample had that at the one year mark. That's a pretty substantial subset.



The charts above show the reduction in power (watts) recorded in the CPET test at 6 months. The participants had to have a reported fatigue level of 7 or more. (I'm not sure if all the participants in the study had to have fatigue rated at least a 7 at 6 months - I think they probably did.)

 

The authors seem to flop about in numerous paragraphs on the question as to whether exercise helps Long covid and, particularly, ME/CFS. It's as if two different authors with two different ideas took charge of different paragraphs. They seem to come down to the conclusion that exercise is good for Long Covid, but that it needs to be approached much more carefully in ME/CFS. But, they don't say how to identify the people with ME/CFS.

It's not completely clear what selected subjects they are referring to; I think it's their whole 506 people sample at the six month mark. They seem to be saying here that neither gender or the undertaking of physical activity made a difference. But that after the 6 month mark, at 12 months, the 'historically active groups' reported lower fatigue.

I guess this study might suggest that if you were young and healthy and you have symptoms largely compatible with ME/CFS at six months, you have very good odds of being essentially recovered, or at least very much improved, at twelve months.