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Comment by fragsworth | Hacker News Reader

I worry sometimes about the actual effects of exercise on our health, and the legitimacy of these studies. It's impossible to detach these studies from the confounding factors - if your health declines (for any reason), you will stop exercising. I feel like we have to take any studies that use correlations with a grain of salt.

How do you study the effects of exercise when there are such massive confounding variables?

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Well, it's entirely anecdotal, but there's a book devoted to the walking habits of many prestigious philosophers and other artists and thinkers: https://www.versobooks.com/books/1865-a-philosophy-of-walkin....

Sure, any conclusions you can draw from this don't have the rigor of those drawn from carefully accumulated scientific observations and controlled experiments...but it's also possible to be such a stingy devotee of scientism that it paralyzes you and divorces you from truths that are otherwise intuitive and simply a part of being human.

If you try to incorporate exercise into your daily routine you'll also have a direct experience of its benefits.

We don't necessarily need science for everything and we also don't need to establish proofs for everything. A clouded, unflagging allegiance to the scientific method is what distinguishes a dogmatic acolyte from a rational thinker (just as it does the religious fanatic and the rational practitioner)--it's just as important to circumscribe the space of the actual utility of science just as much as it is to stand firmly by its methodological principles.

I exercise a lot. But I do it mostly for the intrinsic fun part.

I doubt it has a big impact on our health and longevity. Once a research says regular medium intensity exercise could potentially prolong our lives by 3 to 5 years. But that is it. If you exercise for 50 years, 3 times a week, and 1 hour per session plus 30 minutes preparation, that is actually 12150 hours in total and translates into about 2 years of productive life.

So its ROI from a longevity perspective is really not as high as some of us think.

The ROI argument is one reason why I commute by bike. 7 days a week no problem, no real preparation time. Takes up time I would otherwise be wasting sitting in a car or public transit.

Last week according to my log I rode for 213 minutes. That's a bit more than 30 minutes per day.

I have done the same and it's great.

The main issue is that I used to spend the commute reading books. So I have basically exchanged "mental" excericse with physical excercise. I feel that listening to an audiobook while cycling is a bit too dangerous for an urban commute like mine.

I really sympathise with this. I changed job about two yeas ago and switched from an hour long train ride to a 30 minute cycyle. The shorter commute is great, and the in built exercise is great, but man I really miss that chance to read, or just relax.

Why not get into the habit of reading in bed for a while before sleep? It helps the brain wind down, and is easy to maintain as a habit.

I have all my best ideas while riding my bike. It’s mental exercise of a different sort.

You have to take into account that riding a bike is way more risky than using a car.

And also more fun, better for the planet, far less expensive...

How do you measure risk? Done consistently over a long period, driving a car instead of riding a bike if possible will make you fat and age quicker.

I swapped jobs so that I could ditch the car and am slowly reversing the damage.

Citation requested.

I've been looking for information on risk, overall, by passenger miles travelled, by trips, and by time-in-mode (which adjusts for typical trip length).

Only partially successful, though I find:

30,690 overall auto fatalities.

- 6,067 cycling & edestrial fatalities, combined.

- "More than 90% of pedestrian fatalities occurred when the victims were hit by automobiles and light trucks."

- "A related study on risk factors for on-road cycling commuters indicated that prior to car-bicycle accidents, 89% of cyclists were traveled in a safe and legal manner. In addition, vehicle drivers were at fault in 87% of the events."

https://journalistsresource.org/studies/environment/transpor...

The risk externalities of motorised vs nonmotorised transport appear far greater.

The parent didn't mean to say whether cyclists or drivers were more or less at fault, but for every minute/mile spent on a cycle instead of a car, the likelihood of injury is probably higher.

Understood. However it's interesting to note that motor vehicles are the major source of cycling risk, all the same.

It probably depends on where you live and the (lack of) appropriate infrastructure.

As a Dutchman I can safely say riding a bicycle is just as safe/dangerous as riding a car — statistically speaking that is.

The risk of cycling depends on many different factors and is not simply described as "way more risky than using a car".

Per distance, the average cyclist has more risk than the average driver. However, that's just the base rate, and is not destiny. Combine that with the fact that cyclists tend to travel much shorter distances than drivers. So much shorter that based on distance alone I've seen some cyclists argue, with statistics for average cyclists no less, that they actually face less risk on the road than many drivers. You don't see drivers with long commutes getting warned about the danger, but if people treated driving the same as cycling you would.

There are many things cyclists can do to reduce their risk per mile. As I recall, the majority of cyclist deaths involve riding after midnight or riding when drunk. If you don't do either then your risk is a lot lower. I've been riding for over a decade now and recognize the importance of where you live, infrastructure, defensive cycling, visibility gear (lights, vest, reflectors, etc.), and even a simple air horn.

Also recognize that cycling gets safer every year on average, even in the US. At some point I looked at the data and recognized that the cyclist mortality rate in the US is decreasing roughly linearly. If the linear trend continues then there will be roughly zero cyclist fatalities in 2050. Of course, it's more likely to taper off. But I never see the fact that cycling is becoming safer every year mentioned by its detractors.

Brief discussion of the data here:

https://predictionbook.com/predictions/133189

With all of this being said, yes, I do believe that cycling is more risky than I'd like. The reason why appears to be that the majority of road users (mostly drivers) do not take safety seriously. In my experience the road users who take safety the most seriously tend to be either cyclists or motorcyclists. No surprise why.

I exercise every day for at least an hour. Screw longevity, I do it to help me think. It’s a great way to step away from work and life for a while, focus on something fun, and the ability run a marathon will come handy in the next zombie apocalypse.

Or during any sort of emergency really. Being fit has many practical uses.

Being fit helps project a certain image. And that is one reason I do it.

Rather than thinking purely about lifespan it would be better to think about healthspan. What if exercise means the years you are living are much more enjoyable and pain free.

I decided to run every day at the beginning of the year. Previously I would go for a lackluster jog every couple of weeks. That was not enough exercise and I went cold-turkey, no excuses. I mostly succeeded aside from a few days where it was not possible due to circumstances. I do not feel that it improved me mentally but physically it's a whole different story. Endurance improved dramatically, I do no longer feel exhausted after physical activity.

At first it was a struggle but now I look forward to the daily run. I do not want the effects to wane and that alone motivates me.

I'm aware that running is hard on the joints. Not sure about my long term plans but I will dedicate at least this year to it.

I guess my point is: no matter if it's running, walking or another activity: just continue doing it and eventually you'll enjoy it.

Running with proper form is really not hard on the joints. That's an old myth.

https://www.webmd.com/fitness-exercise/features/does-running...

> I doubt it has a big impact on our health and longevity

It definitely has an impact on your quality of life and helps you attain your genetic potential. If you're body is prone to cancer or alzheimer you will still get them, but until then you'll be in top physical condition.

When you're 40 and start packing up weight, can't run nor climb 3 flights of stairs without panting, can't lift your kids, can't help your friends move to a new flat, &c. fast forward 20 years and you can't get out of bed without pain, walking is a chore, stairs are your nemesis, your back pain is a constant reminder of your unwillingness to exercise.

> translates into about 2 years of productive life.

I don't think making a distinction between "productivity time" and "staying in shape time" is a good thing to do. You better shave off time by working part time than shave off time by skipping physical exercise. Life doesn't have to be all about productivity.

jogging makes my day 3x brighter

even if it only gives me 1 absolute year more alive, it will yield 50 years of chilly smooth days.

"Health" is a loosely defined word and there are many goals and metrics. We can definitely study some metrics of "health" and study them with high confidence if the goal is well defined and it can be monitored with fine granularity. For example, if many people exercise and then the blood glucose drops for the next day, we can see its good effect, and probably it's easier to figure out what hormonal mechanism or neural pathway affect them.

If the goal is higher-level health issue, like longevity, it is trickier because of, as you said, many confounding issues. I suspect there would be cyclic causality between exercise and longevity/overall health, and it would be quite difficult to separate the cause and the effect. IMO, maybe the best way is, making educated guess based on the studies with clearer metrics.

You seperate out the variables and study people who can exercise, but don’t?

People who exercise are different from those who can but don’t, just as those who smoke are different from those who could, but don’t. People who exercise almost certainly have higher energy levels to start with and are less likely to have lingering minor injuries, just as you’d expect smokers and former smokers to exhibit higher levels of addictive behaviour like high coffee or cola consumption than never smokers.

Epidemiology and nutrition have massive problems teasing out causation because people who X are different from people who don’t X in many more ways than in just that difference. The health benefits of wine over beer probably reflect socioeconomic differences in consumption for just one example.

If you think like that you quickly stop looking at studies, it's impossible to control for every variables, even for the most simple phenomenons. We do our best and most of the time it's enough.

I'm not a researcher, but it seems your logic goes the other way, too: if you walk and your health improves, then there seems to be a positive correlation between health and walking.

And, I think we can control for the health decline. I.e., Stopping exercise because you have cancer vs. stopping because you have broken leg. And even then you can control for changing up the type of exercise. My wife broke her foot last year, and shifted from running 20 miles a week to doing "sit and bit fit" exercise. She actually improved her cardio capacity.

Finally, I think the logical conclusion of your argument is: exercise has no impact (or maybe even a negative impact) on health. Studies and every day experience don't seem to bear this out.

Same with diet studies which is why mechanisms inside the body are important to study and identify.

Seems like you could A/B test diet for people getting all their food from an institutional cafeteria. Students, soldiers, prisoners, etc.

For every lifestyle decision, there are always potential risks and potential benefits.

For example, people who run excessively tend to lose fast-twitch/bulk muscle mass and wear their hips, knees and ankles faster than most people. For example, one of the worst things you could do to your body would be to repeatedly run fast, downhill while letting your feet slap the ground.

And, you're never going to be able to measure all of the pluses and minuses intellectually or quantitively, which is why these choices tend to be primarily qualitatively-based with some quantified-self bits on the margins.

For example, people who run excessively tend to lose fast-twitch/bulk muscle mass and wear their hips, knees and ankles faster than most people.

Pay for the exam, I'll debunk this one right away.

And I believe the whole, "Running is bad for your knees" argument has been debunked,

https://omrf.org/2016/09/12/is-running-bad-for-your-knees-su...

For example, one of the worst things you could do to your body would be to repeatedly run fast, downhill while letting your feet slap the ground.

I think falling off a cliff repeatedly would be a slight bit worse. Or taking up a meth hobby. Or other things that seems fairly obvious.

I do a lot of trail running on steep trails (or no trails!) My knees are fine. As mentioned, lots of worse things to do to your body. Here's another one: take up skiing.

Not the most unbiased source, I'd say. And no link to the research.

Here's a link to research.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5179322/

It's actually an interesting read. But if you read it you will see that one must be careful about what to conclude from that.

You're just asking how do we control for confounding factors in epidemiologic research. There are many ways, included adjusted logistic regression modeling, propensity scores, randomized clinical trials, cohort studies, on and on. I know it may seem like there's too many studies, but you shouldn't worry that there aren't extremely intelligent statisticians and epidemiologists working on these very issues - I collaborate with them daily :)

I hate how hard it is to sort out truth from fiction when it comes to new science regarding health and especially dieting. One study says one thing, another says another. How does anyone sort out fact from fiction on these things if they've never been to medical school?

Not a real researcher, but perhaps randomized trials could help?

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