I have a question about classes of muscle fibers: I have seen both type IIb and type IIx muscle fibers from different sources, but no sources include both. Are these just different names for the same thing?
Yes, they are both the same type of muscle fibers. (fast-twitch)
Based on my (1 minute-long, admittedly) research, they are different (I found a source discussing the effects of the ratio between the two types).
Really? On http://greatist.com/fitness/what-are-fa ... ch-muscles
, they are both referred to as the same thing.
This quote - "Fast-twitch muscles break down into two categories: moderate fast-twitch (type IIa) and fast-twitch (type IIb or IIx
)." explains it.
Here is another quote from http://athletics.wikia.com/wiki/Type_II_Muscle_Fiber
. "Type IIb fast-twitch fibers, or fast glycolytic fibres (also known as Type IIx
), are recruited for very short-duration high-intensity bursts of power such as maximal and near-maximal lifts and short sprints.
Could you please link me to the article that you found