As I remarked in another comment, exercise has documented effect. It is rational to do not just for health but for cognition (so why don't I exercise?
Well, why don't you? And everyone else who complains about their "somehow" not exercising. It's a common complaint, even here on LW, where one might expect people to have already risen above such elementary failures of rationality.
This is not a rhetorical question. I speak as someone who does exercise, as a matter of course, every day, and have done for my entire adult life. (Before then, I wasn't averse to exercise, I just didn't give it much attention.) So I do not know what it is like, to not be this person.
So, what is it like, to be someone who thinks they should be doing that, but doesn't? What is going on when you see in front of you the choice to bike to work, to do 20 press-ups right now, to get a set of dumbbells and use them every day, or whatever -- and then not even click the "No" button on the dialog floating in the air in front of you, but just turn away from the choice?
Likewise, every other actual practice that you think would be a good thing for you to do. If you think that, and you are not doing it, why?
Calling it akrasia looks like a way of getting to not fix it.
From my experience, I can say that my motivation is external to me.
In summer of 2007 I got up at 5 AM and jogged because I read a motivational article and discovered that I like witnessing the sunrise. My motivation dissipated as soon as autumn came. Last summer I resolved to lift weights but failed. This year I read Playing to Win and saw a friend of mine who has been exercising for a year; and now I'm going to the gym three times a week.
So why am I not doing this or that? Because I lack a suitable source of motivation.
Transhumanists have high hopes for enhancing human cognitive abilities in the future. But what realistic steps can we take to enhance them now? On the one hand Flynn effect suggests IQ (which is a major factor in human cognition) can be increased a lot with current technology, on the other hand review of existing drugs seems rather pessimistic - they seem to have minor positive effect on low performers, and very little effect on high performers, what means they're mostly of therapeutic not enhancing use.
So, fellow rationalists, how can we enhance our cognition now? Solid research especially welcome, but consistent anecdotal evidence is also welcome.