Hormones, secreted by endocrine glands in the body,
are substances that regulate the function of body cells, tissues, organs or
systems. Hormones are released from a number of “traditional” glands, such as
the pituitary, testes, ovaries, pancreas and thyroid and the adrenal cortex.
More recently, science has also documented hormone secretion from
“nontraditional” sites, such as the heart, kidney, liver and adipose tissue. In
reference to gender, the major distinctions between male and female
endocrinology (the study of hormone-secreting glands) come down to differences
in the reproductive structures (testes versus ovaries). Males produce high
levels of testosterone and much lower levels of estrogen and progesterone;
females produce high levels of estrogen and progesterone and much lower levels
of testosterone.

Exercise places a major challenge on the body owing to the
increased energy it requires and the physiological demands it puts on the
body’s nervous, muscular, cardiovascular, metabolic and respiratory systems. As
a body responds and subsequently adapts to exercise, a number of complex
hormonal interactions occur simultaneously. For example, hormones can increase
blood pressure, stimulate protein synthesis and increase the body’s metabolic
rate. Several hormonal responses and consequent adaptations to resistance
training are discussed in this article.

Energy Production

With resistance exercise, there are
immediate increases in epinephrine and norepinephrine (Kraemer & Ratamess
2005). These two hormones raise blood glucose and are important for increasing
force production, muscle contraction rate and energy production (i.e., the
synthesis of ATP—the energy currency of cells). Levels of these hormones
actually begin to rise prior to the resistance training workout (Kraemer &
Ratamess 2005); this is an anticipatory response of the body preparing for the
challenging exercise to follow. In­terestingly, the elevated blood glucose
levels do not typically lead to an increase in insulin unless
protein/carbohydrate supplementation precedes the workout (Kraemer &
Ratamess 2005). The greater uptake of blood glucose by the skeletal muscle
occurs because of an increase in function by the cell’s glucose transporters,
which raises metabolism in the muscle cell. Regular resistance exercise
training has been shown to increase insulin sensitivity, meaning the body can
take in and use glucose more effectively (Pollock et al. 2000).

Training Volume

In resistance exercise, total volume is
easily calculated by multiplying number of repetitions (reps) x
number of sets x weight in either a single session
of resistance exercise or a long-term resistance training program. Marx et al.
(2001) examined the long-term training (6-month training regime) adaptations
as­sociated with a low-volume (circuit) resistance training program versus a
periodized, high-volume resistance program in college-aged women. The study
found that subjects who followed the periodized, high-volume resistance program
had higher levels of testosterone and insulin-like growth factor-1 (a
muscle-building hormone) and lower levels of cortisol after 24 weeks of
training compared with subjects who followed the circuit program. Greater
increases in muscular strength, power and speed were also seen in the
high-volume group.

Smilios et al. (2003) examined the acute effects of the number of
sets on testosterone, cortisol and growth hormone responses after a maximum
strength protocol (5 reps at 88% 1RM, 3-minute rest) and a muscular hypertrophy
protocol (10 reps at 75% 1RM, 3-minute rest). The subjects—11 physically active
young men with 2–8 years’ resistance training experience—performed 2, 4 and 6
sets of each exercise. Subjects also did 2 and 4 sets of a strength endurance
protocol (15 reps at 60% 1RM, 1-minute rest). In the muscular strength
protocol, the number of sets did not affect the hormonal profile. In the
muscular hypertrophy and strength endurance protocols, there was an increase in
cortisol and growth hormone levels when 4 sets were performed versus 2. In this
study, none of the testing conditions resulted in a significant increase in
testosterone levels. Contrary to that finding, Kramer and Ratamess (2005) have
summarized that protocols high in volume do
tend to produce acute hormonal elevations in testosterone (as well as cortisol
and growth hormone).

Training to Failure Versus Not to Failure

In a unique study, Izquierdo et al.
(2006) examined hormonal responses to 11 weeks of resistance training either to
failure (one group) or not to failure (second group), followed by a 5-week
peaking period involving a maximal strength and power protocol (identical for
both groups). Subjects were 42 physically active males randomly assigned to the
two groups. The results showed that 11 weeks of training to failure or not to failure
resulted in similar gains in 1RM strength, muscle power output of the arm and
leg extensor muscles, and maximal number of repetitions in the squat. How­ever,
after the identical 5-week peaking period, the not-to-failure group showed
greater increases in strength, power and resting testosterone levels and
greater reductions in cortisol levels compared with the failure group. The
failure group did show a greater increase in muscular endurance measured by
bench press repetitions and a decrease in insulin-like growth factor 1.

Rest Period

In a recent 6-month crossover study,
Ahtiainen et al. (2005) examined the effects of a shorter rest period (2
minutes) versus a longer rest period (5 minutes) during a strength training
protocol that consisted of two heavy resistance training loading sessions per
week for the lower body. The subjects—13 recreationally trained men—trained for
3 months with either the short or the long rest period, and then they switched.
Workout volume (reps x sets x weight)
was equal in the two protocols. The study found that the length of the rest
period did not affect the magnitude of change in subjects’ strength, mass or
hormonal profile (testosterone, cortisol and growth hormone).

Concentric Versus Eccentric Training

During conventional resistance exercise,
there is sequential concentric and eccentric muscle action. Durand et al.
(2003) found that in training adaptations and hormonal responses, concentric
muscle action produced more growth hormone than eccentric muscle action. These
researchers used the same absolute
load when comparing the two types of muscle actions. Of interest, however: in a
study by Kraemer et al. (2006), which made the comparison using the same relative load, concentric and eccentric
muscle actions produced similar growth hormone and testosterone responses.

Forced Versus Maximum Repetitions

Forced repetitions are a popular method
for adding intensity to a resistance training program. Forced repetitions
are repetitions performed after a person has gone to failure. This type of
training requires the assistance of a trainer (or workout partner). Performing maximum repetitions
is synonymous with training to failure.

Ahtiainen et al. (2004) investigated the hormonal responses of
forced repetitions versus maximal repetitions in eight male weightlifters (with
several years of resistance training experience) compared with eight males who
were not weightlifters (physically active but with no weightlifting experience).
Although hormonal levels (testosterone, growth hormone and cortisol) increased
with both training loads (in both groups), the testosterone increases in the
experienced weightlifters were significantly greater from forced repetitions
than they were from maximal repetitions.

Final Considerations

Resistance exercise has been shown to
have a dramatic effect on acute hormonal responses in the body after training.
These responses play a huge role, not just in immediate tissue remodeling and
growth, but also in long-term strength, power and hypertrophy gains. Resistance
exercise protocols that stress large muscle mass (i.e., that use multijoint
exercises) and are high in volume and moderate to high in intensity tend to
produce the greatest hormonal elevations, thus resulting in optimal muscular
fitness benefits (Kraemer et al. 2005).

SIDEBAR: Practical Applications

There are a number of ways in which trainers can use the
research done on hormonal responses to resistance exercise when designing
client programs.

Energy Production.
During resistance exercise a cascade of events leads to an increase in several
hormones that very specifically help deliver needed glucose to the working
muscle cells for energy production. More energy results in greater work, which
in turn yields greater force production. Therefore, from a hormonal
perspective, personal trainers should encourage regular resistance training
sessions each week.

Training Volume.
Acute and chronic research shows that higher-volume resistance programs tend to
elicit the greatest hormonal responses. Different training regimes, as
accomplished with periodization models, are always encouraged in order to vary
the resistance training stimulus and thus the muscular fitness benefits. For
clients seeking greater muscularity (hypertrophy), trainers should design
programs that have greater volume; for example, by using multiple sets and/or
multiple exercises for body areas.

Training to Failure
Versus Not to Failure.
Taking each set to failure when trying to
increase muscular strength, power and hormonal response may not be as important
a factor for clients as once felt. By taking each set to failure, a trainer may
actually make clients more susceptible to overtraining and to decreased
hormonal and muscle power adaptations.

Rest Period.
Trainers are always working to create the most time-efficient workouts for
their busy clients. Previous research (Kraemer et al. 1990) suggested that a
shorter rest period (1 minute versus 3 minutes) elicited slightly higher acute
hormonal responses. However, a newer study (Ahtiainen et al. 2005) suggests
that changes in strength, mass and hormone elevations do not differ
significantly, whether the rest period is 2 minutes or 5 minutes.

Concentric Versus
Eccentric Training.
From the hormonal response perspective, trainers
are encouraged to vary resistance training schemes to incorporate and emphasize
concentric and eccentric training protocols.

Forced Versus
Maximum Repetitions.
Training programs in which clients take sets to
and beyond failure should be used in moderation. Always taking each set to
failure can have negative effects on strength, power and hormone responses
(Izquierdo et al. 2006). Then again, it appears that the more trained a client
is, the greater the muscle-developing hormonal response will be when forced
repetitions are periodically incorporated.

 


Luis M. Alvidrez is currently in the master’s program in exercise
science at the University of New Mexico (UNMA). He owns “Upward Motion Personal
Training,” which specializes in corrective exercise and lifestyle management.
His research interests include functional training and hormonal responses to
exercise.


Len Kravitz, PhD, is the program coordinator of exercise science
and a researcher at UNMA, where he recently won the Outstanding Teacher of the
Year Award. In 2006 he was honored as the Can-Fit-Pro Specialty Presenter of
the Year and as the ACE Fitness Educator of the Year.

References

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Ahtiainen, J.P., et al. 2005. Short vs.
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Durand, R.J., et al. 2003. Hormonal
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