posted August 01, 2000 03:51 PM            

Anyone who has lifted weights, on and off, for several years is familiar
with the concept of "muscle memory".� Muscle memory in this context refers
to the observation that when a person begins lifting weights after a
prolonged lay off, it is much easier to return to their previous levels of
size and strength than it was to get there the first time around. Even
when significant atrophy (muscle shrinking) has taken place during the
layoff, previously hypertrophied muscle returns to its previous size more
quickly than usual.

A recent study looking at fiber type conversions during muscle hypertrophy
may have uncovered a possible mechanism for this phenomenon. For those of
you not crazy about scientific lingo bear with me. Towards the end you
will see what I'm getting at with this study. In this study the
distribution of myosin heavy chain (MHC) isoforms, fiber type composition,
and fiber size of the vastus lateralis muscle were analyzed in a group of
adult sedentary men before and after 3 months of resistance training and
then again, after 3 months of detraining. Following the period of
resistance training, MHC IIX content decreased from just over 9% to 2.0%,
with a corresponding increase in MHC IIA (42% to 49%). Following
detraining the amount of MHC IIX reached values that were higher than
before and during resistance training, over 17%! As expected, significant
hypertrophy was observed for the type II fibers after resistance training,
and even remained larger than baseline after 3 months of detraining.

Myosin heavy chain isoforms, or MHCs, refer to the types of contractile
protein you see in a given muscle fiber. MHCs determine how the muscle
fiber functions. MHCs are what make a fiber "fast twitch", "slow twitch",
or something in-between. Certain MHCs are known to undergo a change in
response to resistance exercise. In this case, fibers that contain MHC IIX
are fibers that aren't really sure what kind of fiber they are until they
are called to action. Once recruited, they become MHC IIAs. So, fibers
containg MHC IIX proteins serve as a reservoir of sorts for muscle
hypertrophy because the can transform themselves into fibers containing
MHC IIX which grow easily in response to training.

Like any great study, these researchers found what they expected as well
as a little extra that they didn't. I think this study caught my attention
because it showed a long-term alteration in skeletal muscle following
resistance training. It has been this long-term change that has been the
focus of my own training philosophy, which incorporates what I call
"strategic deconditioning". This study showed that resistance training
decreases the amount of MHC IIX while reciprocally increasing MHC IIA
content. This was expected and has previously observed with changes in
fiber type after resistance training. What they didn't expect was that
detraining following heavy-load resistance training seems to cause what
they refer to as an "overshoot" or doubling in the percentage of MHC IIX
isoforms, significantly higher than that measured at baseline. What does
this mean? It could mean that there are more fibers available for
hypertrophy (growth) after a lay off from training than there are before
you start training. This could very well explain the "muscle memory"
effect many of us have experienced ourselves. It may also have
implications for natural bodybuilders looking to overcome long-standing
plateaus.

There are a few questions that this study did not answer. For instance,
they waited until 3 months after they stopped training before they took
final measurements. It would have been nice if they had taken measurements
regularly so that the optimal period of detraining could be identified
corresponding to peak MHC IIX levels. Because it takes 3-4 weeks for these
contractile muscle proteins to turn over, it would take longer than one
month and probably less time than 6 months (previous research). Still the
optimal time remains to be elucidated.

posted August 01, 2000 04:12 PM            

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"The race is long... and in the end, it's only with yourself."

posted August 01, 2000 05:11 PM            

Nice post. Keep 'em coming.

Bjaarki

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"'Til the weard of the world, stands, unforgotten,
high under Heaven, the hero's name." - Hrolf Krakki's Saga (Iceland)