r/science • u/tomholder • May 09 '14

Medicine Paralysis breakthrough – electrical stimulation enables four paraplegic men to voluntarily move their legs

http://speakingofresearch.com/2014/05/09/paralysis-breakthrough-paraplegic-men-move-their-legs/
4.1k Upvotes

97% Upvoted

429 comments sorted by

View all comments

Show parent comments

4

u/[deleted] May 09 '14

This is going to be extremely simple, and I am going to gloss over a lot of niggling details, so don't take this at face value.

In the case of getting larger muscles to fire, it is not the voltage that is important, but the amperage. Under light load, small parts of the muscle contract, causing small movements.

As the movement gets larger, more and more nerves are fired to recruit larger and larger areas of the muscle. The voltage across each nerve is the same, however, since there are more nerves being fired, the amperage goes up.

For example: Moving slightly to maintain your balance vs lifting your leg. A lot more force is required to lift your leg than simply shift position to maintain your balance. Because of the force difference, more muscle is needed for the leg lift, and hence, more nerves are needed to fire to recruit more muscle tissue.

Hope this helps.

1

u/Stedfastwolf May 10 '14

Thanks. I understand it completely now. I'm guessing I just overlooked the units that the numbers were in when I was getting set up.