Do the low rep sets first. If you were to do the high rep sets you would create pre-mature ATP depletion and lactic acid build-up in muscle. Also, a 10-12 rep set in not high enough to exclude Type II (fast twitch) fiber, and these fibers are not resistant to fatigue at all. Type II fibers have the laargest potential for hypertrophy so fatigeuing them before actually training them would not be very wise.
On the other hand, training in the 4-6 range will stimulate the Type II fibers to the exclusion of the Type I (although the IIA's will be invloved, but they share the same hypertrophy potential as IIB's, and are actually regareded as more important), therefore training your Type II's will not fatigue your Type I's, but of course the pre-mature ATP depletion will still be a problem as well as lactic acid build-up, but it won't be as *much* of a problem if than if you trained the high rep range first.
Additionally, training Type I fibers does not train the nervous system to any significant degree, which should be a very important concern. You can't maximally stimulate muscle until the nervous system is optimized to do so, and fatigueing your IIB fibers before training them will limit the amount of stress you are able to put on it.
In conclusion, do you heavy sets first, and do your light sets afterwards.
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Complex problems have simple, easy to understand, wrong answers.
<FONT COLOR="#000002" SIZE="1" FACE="Verdana, Arial">[Edited 1 time by TheSupremeBeing on 07-05-2001 at 01:29 PM]</font>