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)