So what exactly is meant by “systemic?”
It means that when we lift a weight several things happen. At the level of the muscle, there
is controlled damage to the myofiber during muscular contraction. This damage (known as
micro-trauma) leads to remodeling (growth) of the muscle predominantly takes place during
the eccentric (negative) part of the rep.
Simply put, at the local level of the muscle fiber, it is the lowering
(negative) part of the exercise that is responsible for most of the
damage to the fiber that (hopefully) leads to muscle hypertrophy
and increases in strength.
From this information we can conclude that a controlled rep,
where the weight is lowered under full control, is a particularly
important part of a properly executed rep.
Now this is what is happening at the local level of the muscle fiber,
but as I said before, muscle growth is ultimately controlled by
the effects exercise has on the entire system. For example, as any
bodybuilder knows, growth hormone is one of several anabolic
hormones important for increasing muscle mass and shedding
body fat.
Growth hormone is a key anabolic and lipolytic (fat mobilizing) hormone that many bodybuilders
are injecting pre-contest and off season to build additional mass and burn fat. However,
growth hormone (GH), insulin, human growth factor one (IGF-1), and to a lesser degree
testosterone, can be partially manipulated by diet and exercise, so don’t think an elephant
pituitary extract enema is the only way you will ever add new muscle!
The metabolic costs of exercise can be shown in this example: When we lift weights we cause
a rise in lactic acid. Research suggests that the signal to release growth hormone in response
to exercise is related to the level of lactic acid in the blood. It is a system-wide response to the
exercise (i.e. the increasing level of lactic acid in the blood) that causes growth hormone to
be released.
In fact, the body produces many metabolites and metabolic byproducts in response to weight
lifting that contribute to the growth of lean tissues being trained.
What does this tell us?
It tells us that weight training does not just cause controlled damage to muscle fibers to stimulate
growth but has a systemic effect. It suggests weight training has a high metabolic cost
that stimulates the entire body to respond to the exercise in a positive way.
Another example of a systemic response to weight training is not commonly appreciated.
When a person first starts to train with weights, their strength climbs rather quickly, yet they
put on relatively little muscle. What is going on here? Scientists have postulated that this early
rise in strength in response to weight lifting takes place from an improved efficiency of the
nervous system, that it is a neural adaptive response.
Personally, I believe that the efficiency of the nervous system continues to play an important
role in the process of building muscle even after many years of training, but that’s another
story.
You see, this is an example that demonstrates it is not only what happens to the muscles
themselves when we train, but what happens to our entire system when we train. The nervous
system becomes more efficient, the endocrine system responds, and various enzymatic pathways
are affected. The body’s response to weight training is clearly not a local event relegated
simply to its direct effects on muscle fiber but is actively promoting a systemic response.
These are a few examples of how the systemic response to exercise leads to increases in size
and strength. The metabolic cost of exercise probably plays as crucial a role in muscle growth
as does the local stimulation to the muscles (i.e. myofiber damage caused by intense muscle
contraction).
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