A quick calculation on exercise

The question is—am I doing enough exercise?

I intend to provide a worked example for you to work alongside with your own calculations and decide if you should increase or decrease your exercise.

The benefits of physical activity are various and this calculation can be done for one or all of them; some of them include:

  • longevity of life

  • current physical health (ability to enrich your current life with physical activity)

  • happiness (overall improved mood)

  • weight loss

  • feeling like you have more energy

  • better sleep

  • better sex

  • fun while exercising

  • reduce stress

  • improve confidence

  • prevent cognitive decline

  • alleviate anxiety

  • sharpen memory

  • improves oxygen supply to all your cells

I am going to base this reasoning on “longevity of life” and “everything else”
expected life span:
I am a little lazy; and so I am happy to work with 100 years for now. For bonus points you can look up the life expectancy for someone born when you were born in the country that you were born in. If both of those numbers are not good enough make your own prediction of your life expectancy.
amount of exercise needed to produce optimum benefits:
I believe that any exercise above two hours per day will not do much more to improve my longevity that I could not get out of the first two hours. If the benefits of exercise are something like a power law; then the minimum amount required to get the most exercise can be calculated by taking a graph like this; and drawing your own lines on it as I have.

I think the most benefit can be gotten out of exercise between 30 mins and 2 hours per day.
Just how much longevity do I think I will get?
Oh its hard to say really… Some sources say:
  • 3 years for the first 15 minutes a day and a further 4% reduction in mortality for every 15minutes after that

  • every minute of exercise returns 8 minutes of life

  • being normal weight and active conveys 7.2 years of extra life expectancy

  • 75mins/​week of brisk activity = 1.8years of greater life expectancy with more activity giving upwards to 4.5years of longevity

on top of longevity there is all the other benefits I have not counted very well. For my 100 years; adding an extra 4-7 years is worthwhile to me...
And finally; the disadvantage: opportunity cost
there are 168 hours in a week. With most people spending 13 of that asleep (56hrs, 8hrs/​night), 20 hours on lesswrong per week, 40hours in an average work week, before we take two hours out of each day to spend exercising (14hours); what are we taking those hours away from? Can you do what you were doing before without the time spent exercising here?
I’m not going to tell you how to exercise or how to fit it into your life. I am telling you that its damn well important.
I was going to throw in some bayes and prediction but I have now realised I am pretty bad at it and took it out. Would love some help compiling that sort of calculation. (personal prediction that 30minutes of exercise will increase my life expectancy by 4 years)