This is the point in the article where I could go into a long and unusually boring dissertation
about muscle physiology: Muscle fiber types, controversies over whether the muscle gets
larger or divides into new muscle cells, or both.

Number of reps, volume of training, concentric, eccentric, isometric, etc.: this is important
information for the research scientist, but not all that relevant to the hard training bodybuilder.
I mean, what are we looking for here? In a nut shell, what we want is the correct level of
stimulation to a muscle to make it larger, right? Too little stimulus and the muscle won’t grow.

Too much stimulus and the muscle doesn't grow, or worse yet, gets smaller due to injury or
inability to recuperate. The proper stimulus within a given period of time is what we are looking
for.

This brings me to another point. It is not the amount of actual weight that is the most important
factor to muscle growth, but the actual amount of stress or tension the muscle must endure
during the rep that is the crucial stimulus for growth. But some might ask “ Doesn't using
more weight mean more stress on the muscle?”

The answer is no.

If you take 405 lbs. off the rack when bench pressing and bring it down quickly without control,
bounce it off your chest and lock the elbows out hard at the top for one rep, are you
creating more stimulus to the pec muscles than if you took 300 lbs. off the rack and brought it
down with full control, pressed it up without any bounce or momentum, and did not lock the
elbows out at the top for ten reps?

I think the answer to that question is obvious, and we will examine this particular topic in the
coming sections.

The point I am trying to make here is that weight is only a factor within the variable of how

the rep itself is performed. All things being equal (i.e., each rep is performed correctly for that
exercise) weight does matter.

The more weight you can use in a given exercise, with correct form, in a given time period, for
a specified number of reps, the more stimulus for growth the muscle will experience. However,
using more weight for the sheer sake of using more weight, not taking into account how
the rep is performed, does NOT equal more stress on the muscle.

When we talk about a stimulus for growth, we must look beyond the simple micro-environment
of the muscle fiber in question. This is where bodybuilders and scientists often fall short
when trying to examine the topic of muscle growth. An examination at the level of the muscle
fiber, where the actual damage occurs, is obviously important for any study of why and how
muscles grow from weight training.

However, it is not the only factor involved leading to the increase in size and/or number of
muscle fibers in response to weight training.

When we train with weights using sufficient loads and intensity, we cause micro-trauma to
the muscle fiber(s). That is, at the level of the fiber itself, we have caused a certain amount of
controlled damage to the fibers involved.

However, muscle growth is far more involved than simple breakdown and repair. This is the
point in the report where we need to look at the concept known as the “metabolic cost of exercise.”
This concept, though complex if you map it all out, can still be reduced to its most basic
definition: Muscle growth is not a local event that happens exclusively at the level of the
muscle fiber, but is ultimately a systemic response to exercise that leads to muscle growth.

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).