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Comment by 10ren | Hacker News Reader

Coincidentally, brain scans often show around 10% activation (random google eg. http://www.nimh.nih.gov/science-news/2009/impaired-brain-act...)

Only a fraction of a CPU is active during a given time period (eg if no floating point arithmetic is needed); and we don't use all the muscles in our body most of the time either. That's a bit different from what the pop-psy authors meant though.

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"brain scans" depict no such thing. "10% activation in the brain" is probably a meaningless statement -- the brain is always doing "something" (except when it's dead), and in any case, there's lots of different ways it might be getting "activated" (e.g., learning v.s. doing). That said, it's certainly possible to be mentally lazy, and this would no doubt lead to different patterns of activity than being mentally vigorous.

Usually what these brain scans depict is, more or less, how "different" (brighter usually means larger statistical significance t-values) the oxygen-usage activity of some test state is from the same oxygen-usage activity during some rest state. Google fMRI (or look here: http://www.scholarpedia.org/article/fMRI).

Sometimes this means "less" activity than at rest state. Sometimes this means only very slightly (but consistently) more. Moreover, parts of the brain that vary considerably from trial to trial, but average out to a negligible difference from rest state, would also be easily ignored. This should give some sense of just how many assumptions and calculations have gone in to the pretty brain heat maps that the media are so fond of.

Lots of good and interesting stuff can be and has been figured out using fMRI. That said, figuring out how the brain works using fMRI is like trying to figure out how an economy works by observing CO2 emissions from space, at a resolution of, say, 10m.

In a untrained person, at maximum effort you can activate about 30% of the fibres in a muscle. Not the same 30% every time obviously, that's just what your nervous system has the power to drive. In a trained athlete that goes up to around 50%. Now that's intriguing; if an untrained person could achieve full activation (say in a moment of dire need) they could more than triple their strength...

> Now that's intriguing; if an untrained person could achieve full activation (say in a moment of dire need) they could more than triple their strength...

That one can and does happen. There are recorded instances of seemingly heroic strength where, for example, parents have lifted a car to rescue a child who was trapped underneath.

My research has led me to believe that only an adrenaline surge can produce this.

The thing to note about this is that it essentially impossible to not seriously hurt yourself when you do this. You will tear the muscles. They are operating at their highest power before the wheels start flying off, and you'll tear a lot of fibers.

That is probably because the fibers are handing off work to each other like a baton race, "I'm pooped, take over for me". You might get triple strength - at the cost of sudden collapse a few seconds later when the whole muscle runs out of resources at once.

Edit: in this context, consider the muscle prostration of a person who has been tazed (which forces total contraction electrochemically).

Yeah, that would happen when the ATP was fully converted - so 5-10 seconds.

t-nation.com reckons it's related to nerve signals rather than individual fibres tiring tho'.

That's called "recruitment". If you start weight training, your effective strength will go up fairly quickly for the first few weeks as your recruitment goes up; then it levels off (and at this point most people give up on training) as further recruitment slows and actual enlargement of the muscle fibers begins.

But the false claim is that only 10% of your CPU ever gets used. They're saying you never turn on the floating point circuitry, but you can if you buy this book.

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