Glenn links to this bit of health news from Theodore Dalrymple at PJ Media.
It is meant to be funny, and is, but it has still summoned forth my Inner Pedant, always lurking beneath the surface of this seemingly fun-loving exterior. And not far beneath the surface, either.
The question is, how much exercise provides a health benefit? The theme is set here:
Between 1996 and 2008, the Taiwanese researchers divided 416,175 people into five categories, according to the amount of exercise, on self-report, that they did: from none to a lot. They discovered that those who did a little exercise, on average 92 minutes per week, had a reduction of 14 percent in their all-cause rate of mortality. They also found that “every additional 15 minutes of daily exercise beyond the minimum of 15 minute per day further reduced all-cause mortality by 4 percent.”
The subsequent letter to the Lancet pointed out that this cannot be correct: for if it were correct, and on the assumption that the relation between exercise and longevity were a causative one, Man would be immortal if only he did sufficient daily exercise, something in the region of six hours. In these circumstances, at least in my opinion, life would not actually go on forever; it would merely seem as if it did, in the sense of being boring and pointless.
I remember reading about life extension by calorie restriction and had a similar reaction - these people may live to age 120 by eating ground shirt cardboard and walking around at 6'2", 120 lbs, but it will seem a lot longer. But then again:
''For every calorie you save, there's about a 30-second increase in your life span,'' he said. ''It's worth more to me to have an extra two to three minutes of life than an extra slice of pizza.''
Worth keeping in mind.
But let's not keep the Inner Pedant waiting! The obvious problem with the 'exercising to immortality' hypothesis is that it represents an extrapoloation beyond the experimental range, and we know how problematic that can be.
In fact, the paper itself makes that very point:
After the minimum recommended 15 min a day of exercise, every additional 15 min of daily exercise (up to 100 min a day, after which additional exercise gave no additional health benefi t) is expected to generate an additional reduction of 4% (95% CI 2·5–7·0) all-cause and 1% (0·3–4·5) allcancer mortality.
This gives me an excuse to clip in their cool graph and use the word "asymptotic":
At a more basic level, this paper does not seem to distinguish cause and effect. Rather than randomly assigning large groups of people to the different exercise intensity groups (as if that could be done over a long period), they rely on self-selection and self-reporting. Consequently, as is so often the case with this type of study, we are left wondering whether exercise makes people healthier, or healthier people simply enjoy exercise more.
Well. Make the mock if you will, but those diligent exercisers are lookin' good and feelin' better. Unless they are laid up with some ghastly injury, natch.