The effect of physical fitness on mortality is overestimated

Next, the researchers examined how fitness was associated with the risk of dying in random accidents such as car accidents, drownings and homicides. They chose random accidents because they assumed that there ought to be no association between the men’s fitness in late adolescence and the risk of dying in random accidents. This method is called negative control outcome analysis and involves testing the validity of your results for a primary outcome by comparing them with an outcome where no association ought to be found. If, however, an association is found, it may indicate that the groups studied are not actually comparable, and that the study suffers from what is typically referred to as confounding. The researchers found that men with the highest fitness levels had a 53 per cent lower risk of dying in random accidents. Yet, it is unlikely that the men’s fitness would have such a big effect on their risk of dying in random accidents.

This seems like a completely unsupported assumption.

Physical fitness can make a difference in the survivability of unexpected drowning risk. Imagine a boat overturns and people have to swim to safety. One would expect that the extreme consequence of death would tend to happen to the least fit people in the group, even if everyone experienced the same traumatic event.

How much do bone density and muscle mass affect survivability in car accidents? Does good cardiovascular circulation help with healing, fighting off infection, etc.?

And I'm not sure about homicides. What are the methods of killing, and what percentage of these deaths involve reckless or negligent homicides? Can physical fitness play a role in simply getting away from the danger (whether that danger is intentional, reckless, or negligent)?

So, stay fit so you don't die of random accidents. Got it.

Interesting study. It says, in a nutshell, that it can replicate previous findings that physical fitness in youth reduces the rate of premature mortality due to many conditions, like cardiovascular issues or cancer. That was expected.

Then it looks at the rate of premature mortality due to random accidents (I assume things like car crashes and being run over by trolleys) and finds the same reduced rate, but there should be no correlation.

So something non-causal is probably happening to reduce the stroke, heart attack, and cancer risk of people that were physically active as young adults.