A muscle must be subjected to a stimulus that compels it to adapt and grow. If
there is no reason for a muscle to grow, no hypertrophy will occur. Muscles
increase their strength and size when they are forced to contract at levels
close to their maximum. Much more weight can be lifted with compound exercises
than isolation movements. More weight, more overload and in turn more muscle. A
compound exercise is a movement that involves more than one major muscle group.
It involves a primary muscle and one or more secondary muscles. An example of a
compound exercise would be the barbell squat. The primary muscles are the
quadriceps and the secondary muscles are the gluteus and hamstring muscles.
An isolation exercise targets just one muscle. Isolating a muscle during
resistance training limits overload and muscle fiber stimulation, therefore it
limits growth. Dumbbell flyes are an isolation movement for the chest, removing
the shoulders and triceps out of the movement. A common reason people do flyes
is to shape the muscle. This is impossible to do- you cannot change the
predetermined, genetic shape of your muscles. You can, however, make them bigger
which may appear to change the shape. Isolation movements require less weight
and limit overload. They have their place in any training regimen, but not to
increase muscle size.
Overload is the primary objective when muscle hypertrophy is the goal. Going
through the motions will not produce results, you have to push your body to new
limits in order to see increased development. Since heavy weight is the most
influential stimulus for muscle growth, you must continue to strive for greater
overload. Light weight doesn't do it, nor does moderate weight. Maximum overload
is the only method that will force a muscle to grow. The degree of this overload
ultimately determines the degree of muscle growth.
Muscle "burn" does not stimulate growth, overload stimulates growth. The burning
sensation that training brings on is believed by most to be a sign of a
successful growth promoting workout. Many seek it out and strive to achieve this
burning sensation as an indicator to building muscle. That muscle "burn" is not
an indicator of an optimum workout. This burn is caused by infusion of lactic
acid, a byproduct of glycogen metabolism in muscle tissue. Things like "feel the
burn" are not really what building muscle is about. The burn is a good indicator
of performing an exercise correctly and targeting the muscle properly. You can
get a good "burn" by doing 20 repetitions. However, training at that rep range
does not efficiently overload the muscle.
The muscle "pump" you experience when training is a result of blood actually
being "trapped" in the muscles being trained. It is certainly a good
psychological boost during training and accompanies just about all resistance
exercise. The pump will become greater as your muscles grow larger. Now while
this muscle pump is not really a bad thing, it is not necessarily an indicator
of optimum muscle overload. Many people seek out the muscle "pump" by doing high
repetition exercises. Numerous studies have shown that high-resistance,
low-repetition exercises are more effective than low resistance, high-repetition
exercises in promoting muscle hypertrophy.
The last point to consider is that muscles appear to have a memory effect that
is significantly influenced by the last set that you did. If you finish each
exercise with a heavy set, your muscles remember this and adapt accordingly.
Many people decrease the weight on their last set and "rep out". This is
detrimental to what you are trying to accomplish and will impede muscle growth.
The muscle memory effect is an important physiological phenomenon and should be
used to your advantage in gaining muscle size and strength.

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