8 Ways Strength
Training Creates Change in the Body
Provided
by American
Council on Exercise
Many people start working out to increase muscle size or
become stronger and capable of lifting heavier weights. Strength training with
external resistance can increase strength and stimulate muscle growth
simultaneously. However, there is a distinct difference between training for
maximum force output (strength) and an increase in muscle size. Resistance
training alone does not induce muscle growth; the training stimulus has to
cause either metabolic or mechanical fatigue to initiate the physiological
mechanisms responsible for increasing muscle mass.
Momentary muscle
fatigue is a signal that an appropriate amount of either metabolic or
mechanical stress has been applied. Metabolic and mechanical demand on muscle
tissue can stimulate the mechanisms responsible for muscle growth. Therefore,
knowing how to apply the stress in the right way is essential for achieving an
optimal response from a workout program. If you have a client stuck at a
plateau and you’re looking for a way to kick-start his or her workout program,
knowing how to create the proper stress stimulus on muscle tissue can help you
achieve the results your client wants.
Here are eight things
to know about how to place the appropriate demands on muscle tissue to achieve
your client’s desired results:
1.
Muscle
growth and improvements in strength require activating high numbers of fast
twitch (Type II) muscle fibers. Fast twitch fibers are capable of producing
significant levels of force and are frequently involved in anaerobic energy
production, which makes them most susceptible to both mechanical and metabolic
damage. Type IIb fibers are completely anaerobic
because they used stored adenosine triphosphate (ATP) to provide the energy to
produce a high amount of force in a short period of time. Type IIa fibers produce energy from glycogen in a process known
as glycolysis, which can take place both with (aerobically) and without (anaerobically)
oxygen. Fast twitch fibers have a greater diameter (cross-width) than slow
twitch fibers and are responsible for the hypertrophy, or increased fiber size,
of a particular muscle.
2.
Mechanical
stress refers to the physical forces applied to muscle fibers. Resistance
training causes microscopic damage to muscle tissue, which in turn signals the
biochemical reaction to produce new satellite cells responsible for repairing
the mechanical structures and building new muscle proteins. This is how strength
training to the point of momentary muscle fatigue initiates the physiological
mechanisms responsible for muscle growth.
3.
Metabolic
stress is caused by a muscle producing and using the energy required to fuel
contractions. Moderate- to high-intensity, high-volume strength training
programs use the glycolytic system for producing the energy required for the
involved muscles to work. Anaerobic energy is muscular energy produced without
the presence of oxygen. The result of sustained anaerobic glycolysis is an
accumulation of lactate, inorganic phosphates and hydrogen ions, which elevate
blood acidity leading to an effect known as acidosis. There is a strong
relationship between blood acidosis and the elevated levels of the hormones
that support muscle protein synthesis. When a muscle works to the point of
fatigue or “failure,” it has expended its supply of available energy. This
leads to metabolic stress on the involved tissue.
4.
Mechanical
stress is an important and essential stimulus for creating exercise-induced
muscle growth. Metabolic stress may also be responsible for signaling the body
to initiate the physiological mechanisms responsible for muscle growth. Similar
to the age-old quest of which came first, the chicken or the egg, we’re not
sure which plays a greater role in muscle growth—mechanical or metabolic
stress—because both occur simultaneously, making it difficult to identify which
is more important. However, using a weight heavy enough to cause momentary
fatigue after eight to 15 reps, combined with short between-set rest intervals,
will create both the mechanical and metabolic stimulus that could lead to the
desired adaptations.
5.
When
fast twitch muscle fibers create energy from anaerobic glycolysis, it can lead
to an important adaptation responsible for influencing muscle size. As muscle
cells continually use glycogen for fuel, they will adapt by storing more
glycogen during the recovery phase. One gram of glycogen will hold up to 3
grams of water when stored in muscle cells. Exercising to momentary fatigue not
only elevates mechanical damage to the muscle, it can also deplete stored
muscle glycogen. This results in an increase in muscle size once it is
replenished.
6.
One
of the long-term adaptations to strength training is an increase in muscle
fiber cross-width, which is also known as hypertrophy. As the cross-sectional
area increases in size, the fibers have more surface tension and become capable
of generating higher amounts of force. Muscles with a larger cross-sectional
area of individual muscle fibers are capable of producing greater amounts of
force. Myofibrillar hypertrophy refers to the
increase in size or thickness of individual actin and myosin protein filaments,
which can improve the force-production capacity of the myofibrils. Myofibrillar hypertrophy does not lead to larger muscles;
rather, it results in thicker muscle fibers capable of generating more force.
Sarcoplasmic hypertrophy is an increase in the volume of the fluid-containing
proteins responsible for tissue repair in the intercellular space that
surrounds an individual muscle fiber. Sarcoplasmic hypertrophy can cause the
cross-sectional area of muscle fibers to increase, but most of this growth is
due to the volume of the sarcoplasm and non-contractile proteins not directly
involved with force production. Despite a common misperception that lifting
weights can lead to an immediate increase in muscle size, it can take eight
weeks or longer for significant muscle growth to occur, even in a well-designed
program.
7.
Compound,
multijoint movements with free weights such as
barbells, dumbbells and kettlebells involve a number of different muscles and
can generate metabolic and metabolic stress during training. This is especially
true when performing eight to 15 repetitions, with momentary failure occurring
at the last repetition. Selectorized machines that
focus on muscle-isolation or single-joint movements allow mechanical stress to
be placed directly into localized tissue. Free weights involve a number of
contributing muscles, which can increase the metabolic demand, while the
stabilization provided by machines allows for heavier loads on specific
muscles. Short- to moderate-duration rest intervals of 30 to 120 seconds help
create a sizable metabolic demand. Completing three to four sets per exercise
ensures an effective amount of stress on the involved tissues. The tempo of
movement should be relatively short (i.e., one to two seconds) during the
concentric phase of muscle action, and should be longer (i.e., two to six
seconds) during the eccentric phase to ensure adequate mechanical strain.
Slower muscle-lengthening (eccentric) actions place a tremendous amount of both
mechanical and metabolic stress on muscle, which makes it an effective approach
when exercising for muscular growth. Specifically, lengthening under load can
create higher levels of damage, which leads to a rapid rise in protein
synthesis to repair the damage.
8.
Drop
sets are another technique for creating muscle growth. A drop set involves
using a set weight for as many reps as possible and then, when fatigue occurs,
lowering the amount of weight used and continuing. Drop sets keep a muscle
under tension for an extended period of time, which means they can induce
significant levels of metabolic and mechanical stress. However, drop sets can
also create extreme discomfort and should only be used by experienced
weightlifters at the end of a workout.
It is not completely
clear whether muscle growth is the result of mechanical or metabolic
overload. What is known
is that the mechanisms for muscle growth are best achieved when an exercise is
performed to the point of momentary muscle fatigue. To stimulate muscle growth,
a strength-training program must be applied in a manner that places a
significant amount of mechanical stress on the muscle tissue, while also
creating a sizable metabolic demand.
Identifying whether a
metabolic or mechanical stimulus is more appropriate for a client interested in
muscle growth will take some trial and error. Some clients may be capable of
tolerating the discomfort that comes with training to muscle failure, while
others may prefer a heavier load for fewer reps to induce mechanical stress.
While both mechanical and metabolic stimuli result in muscle growth, both can
also lead to significant muscle soreness. If a client wants to increase muscle
size or get stronger, he or she must understand what is involved and be willing
to put forth a tremendous effort, thus’ making the phrase “no pain, no gain”
completely appropriate.
Author
Pete
McCall
Pete McCall, MS, CSCS, is an ACE Certified
Personal Trainer and long-time player in the fitness industry. He has been
featured as an expert in the Washington Post, The
New York Times, Los Angeles Times, Runner's
World and Self. He holds a master's
degree in exercise science and health promotion, and several advanced
certifications and specializations with NSCA and NASM.