[bnjmn]

Mostly because they admit those results are not statistically significant (for example, at the bottom of the summary diagram). That said, I admire their honesty, and I hope these results suggest other kinds of experiments to other researchers. Maybe the study just needs to be larger, or longer.

Focusing on specific kinds of mortality might also give stronger results than measuring "all cause" mortality. I say that because it seems like cancer was the biggest killer in these groups. I am not a doctor, but I wouldn't have thought cancer was causally related to (lack of) exercise, the way cardiovascular diseases are believed to be. I'd be interested to see larger studies with enough non-cancer deaths to say something statistically significant about the effect of exercise on those outcomes.

[travisoneill1]

Why even bother doing a study with a sample size so small that a difference as large as 49% is still not significant?

[andor]

They had 1567 participants. Compared to control (HIIT-like), HIIT reduced risk by 1.7% while moderate intensity training increased it by 1.2%. The overall mortality in the control group was 4.7%. For a controlled trial, that seems like a large number of participants (correct me if I'm wrong), they just were too healthy ;-)

I assume the significance problem is inherent to studies looking at mortality as the outcome is very binary and can take a long time to manifest. As an effect on all-cause mortality can be seen as the ultimate metric of how healthy something is, it's probably still worth it to investigate. In this case, they made it quite difficult for themselves by comparing active people to other active people.

It's also possible that they made other observations during the study that are or will be published separately.

[sundvor]

Also, just adding some sugar to this, don't forget that this study was in Norway. Overall health levels would be higher than in, say, USA. I'm talking about weight specifically.

Assuming healthy / not overweight would be a very big assumption to make for the US (as a Norwegian I went to the the USA, once, in 1999, and what I saw there shocked me), where another study could be to monitor mortality outcome of getting weight under control and exercising vs not.

I'd also love to see impact of weight resistance training added to the mix surveyed.

[sriram_malhar]

And not just Norway, but specifically Trondheim. Correct me if I am wrong, but I expect their lifestyle to be even less sedentary than the average Oslo resident. I expect the results to have slim pickings (pun intended)!

[sundvor]

Roger that. But even by e.g. Australian standards (which are a lot closer to the US ones), Oslo is far from sedentary; I didn't even think about buying a car in Norway before I left it, being happy to walk/run, ride or PT it everywhere. Bad diet, alcohol use etc is a lot more common than in Norway too.

[robocat]

HIIT reduced risk by 1.7 percentage points, mortality down to 3% for the high intensity group, from 4.7% for the control group.

The percentage decrease was 37%: Percentage points are not percent!

[travisoneill1]

I read that wrong. I thought that the overall mortality rate in the groups was 1.2% and 1.7%. Didn't realize those were both differences from the control.

[TJSomething]

Because running a large enough study is expensive and it's cost-effective to perform a smaller study to determine an approximate size of the effect. Then, you can design the next study to have enough power to distinguish the expected effect size from the null hypothesis.

Additionally, these results could be aggregated with comparable results to yield a stronger result.