frenchyge said:
So, with all the talk about pedalling smoothness and such, is the thought that 'leg speed training' is really just technique practice, or are there physiological adaptations that produce improvements in leg speed?
I am curious about that very same question. The goal or idea anyway, would be to get the muscles to contract faster consistently, under a load that increases. Intuitively, I would guess, and it isn't much more than that right now, that there is some correlation between this ability and one's mix of type I & type IIa/b fibers.
To that effect, I found a post of Andy's on FGF about muscle type where there is some mention of rate of muscle contraction:
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All types of physical training (i.e., endurance, sprint, resistance) result in at least partial, and often nearly complete, conversion of
type IIb (IIx) fibers into
type IIa. Consequently, even sprint athletes will tend to have a lower-than-normal percentage of
type IIb (IIx) fibers compared to untrained persons (e.g., ~10% vs. ~25%, depending on course on the particular muscle and just how sedentary the control subjects really are), and highly endurance trained individuals will often have few, if any,
type IIb (IIx) fibers (generally <5% even in a mixed muscle such as the quadriceps). It remains controversial, however, whether it is possible to cause conversion of
type IIa into
type I - the genetic "machinery" is obviously there, and animal studies using chronic electrical stimulation for 8+ h/d have clearly shown such inter-conversion to occur. On the other hand, it hasn't been possible to obtain definitive proof of such fiber
type conversion as a result of training in humans, although there is plenty of evidence (e.g., presence of fibers expressing both
type IIa and
type I myosin) suggesting that it does occur to at least a limited extent. My personal interpretation of the literature with respect to this question is therefore that the fast-vs-slow phenotype is one of the least "plastic" of muscle properties, and as such requires a very large stimulus to cause even relatively small changes.
Finally, note that while human fibers are "typed" based on the myosin isoform that they express, this is not the only factor that
determine the speed of contraction/relaxation of a muscle.
Specifically, even with endurance training type I, or slow-twitch, fibers tend to become faster contracting, whereas type II, or fast-twitch, fibers tend to become slower contracting, irrespective of any change in myosin. Thus, with respect to your real question - i.e., what changes in my muscles account for the changes in my performance as I've transitioned from road to track? - what happens to fiber
type as it is formally defined really doesn't matter.
That is, if the force-velocity properties of your muscleS have changed (and they almost certainly have), then you have effectively become more "fast twitch like", regardless of what a muscle biopsy might show.
One more section:
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The answer to that question is that the mechanical 'machinery' of muscle is composed of numerous proteins, and while the primary (well, along with actin) protein, i.e., may remain the same, others (e.g., the myosin light chains) do "switch" as a result of training, thus modifying the fiber's maximum speed of contraction. There are also changes in calcium handling (i.e., the rate at which it is pumped back into the SR) that influence the speed of relaxation, and hence how quickly you can repeatedly turn force production on and off.
These changes, of course, are in addition to changes in the pathways of ATP provision, although the effects of sprint training here are far, far less than the effects of endurance training (which can result in up to a doubling of mitochondrial respiratory capacity, and equalization of this pathway in
type II and
type I fibers).
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(Emphasis added) - so perhaps there aren't studies but the point is to make one's muscles behave more like FT regardless of their original content?
Also, is this question of 'leg speed' improvement an old-school belief ala SE training or does it have some validity? Yes I know many people do it, but is there something other than experience and tradition to show that it works?
