Comment by stygiansonic | Hacker News Reader

Comment by stygiansonic | Hacker News Reader

A lot of comments are claiming this study shows that exercise is good for your health. Though I generally agree with that premise, that is NOT what the results of this study show. The abstract and visual abstract clearly state this.

- The RCT was done only on individuals aged 70-77

- Furthermore the results were not statistically significant at p < 0.05. You can see this in the visual abstract where the 95% CI overlaps with risk ratio = 1.0, where 1.0 means "no difference" between the groups.

Note that the results being non-stat sig does not mean that there was no difference! It means that the difference, if present, was probably too small to detect given the power (number of participants) included in the study. This is important to understand!

Furthermore, in the "Strengths and limitations of this study" they clearly outline some reasons why the results may have been non stat-sig, including:

- "Firstly, participants in the control group had a high level of activity throughout the study, and many exercised using HIIT. This might have affected the study’s ability to detect statistically significant differences between groups."

- "selection bias might have influenced our results, as participants were more active and had better overall health than non-included participants"

Basically, even the "control" group looked like they had a good baseline level of activity, decreasing the activity level difference between that and the two treatment groups.

My takeaway from this study is that in isolation, it doesn't provide much evidence for or against the effect of exercise, but taken together with other studies can be used for evidential value.

The results can also be used to inform future studies. The authors clearly understood this when they stated in the main measure outcome: "An exploratory hypothesis was that HIIT lowers mortality more than MICT."

Firstly, participants in the control group had a high level of activity throughout the study, and many exercised using HIIT.

I absolutely get why they had to use a control group that was decently in shape, otherwise the effect size compared to the sedentary would probably have been so massive as to be comical and uninformative. But…where are they getting 75-year-olds who are doing HIIT? Is Norway full of septuagenarian gym rats and cross-country skiers?

Well the paper clearly states that they interviewed 6966 septuagenarians and 5114 of them "declined to participate".

Reading the study, participating in our was quite commitment. No wonder people declined.

HIIT is relative to your shape, so their workout was not the same as 24 years old dude in shape would have.

Still, going at 90% of your maximum heart rate repeatedly for two-three minute intervals is really hard work, at any age and shape.

And as others pointed out, the baseline group here is probably a force of nature unto themselves. 75-year old Norwegians were born into a poor country just starting to recover from war and occupation, where most people were farmers or fishermen. It was not until these people had been working adults for 10 years that Norway discovered oil and began its rapid economic growth, by that time these people were used to hard work.

Then you take that generation, and select the toughest portion out of those who say they are interested in participating in a scientific study on exercise, so a two stage selection of fit people.

Basically the baseline here consists of people who think hiking in the mountain for several hours is great fun, and that it's been a bad week if they have not done so twice.

> Basically the baseline here consists of people who think hiking in the mountain for several hours is great fun, and that it's been a bad week if they have not done so twice.

Isn't it like, almost everyone? Except possibility to do it twice a week. Most people I know think hiking in the mountain is great way to spend holiday and they are not particularly tough.

> Is Norway full of septuagenarian gym rats and cross-country skiers?

Compared to the rest of the Europe, yes.

Article based on Eurostat data: https://qz.com/922865/people-in-nordic-countries-exercise-mo...

That level of baseline activity could explain why the MICT actually increased the all-cause-mortality risks. It appears the the mixed control group means that the MICT was actually reducing the average exercise intensity from the norm. What a frickin' overachieving set of septuagenarians (reminds me of Mr. Awesome in Chuck)! I'd assume if there were more "no/low" exercise group the MICT would appear much better. Tantalizing results though.

The control group wasn't assigned to do their regular level of exercise, but rather to follow an exercise routine based on the Norwegian government's existing recommendations. The authors expected a 10% 5 year mortality rate based on population-wide estimates, and their control group had a 4.7% 5 year mortality rate.

Is Norway full of... Nordic skiers?

Indeed!

In seriousness, Nordic (cross country) skiing is an activity enjoyable well into old age. Having done a couple non-competitive “races”, I’m always amazed at the range of ages.

...Adorable old timers with perfect form just slowly gliding across the snow for hours.

There's also some potential for selection bias in the drop-out rates:

>The numbers of drop-outs after one, three, and five years of follow-up were 76 (19%), 104 (26%), and 132 (33%) in the HIIT group, 58 (15%), 76 (20%) and 101 (26%) in the MICT group, and 61 (8%), 95 (12%), and 156 (20%) in the control group.

In other words, the entire observed effect may be due to HIIT being better at making unhealthy subjects drop out of the study.

Nope, I think you may have missed a paragraph:

> but all participants were included for statistical analysis of the primary outcome (intention-to-treat approach).

I think this study looks rather solid.

I think that's a valid point but it may not make a significant difference. Judging by the fact that the control group had a pretty decent drop-out rate it appears that the drop outs reverted to lower than average physical activity levels. I am playing devil's advocate here, but you can't rule out the hypothesis that trying a bit of HIIT convinced more people to take it easy at their age.

I think I see the point you are making now. If HIIT to a greater degree prompts less fit participants to drop out than in the other groups, it might skew the results. Not really sure in what direction though. If it had been a study on the effect of HIIT vs less intense training on cardiovascular fitness, this kind of dropout would bias the results in the direction of HIIT. I have no idea of what effect it would have when the variably of interest is mortality.

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