Advances in Physical Education
2012. Vol.2, No.3, 99-102
Published Online August 2012 in SciRes (
Copyright © 2012 SciRes. 99
Investigation of Beta Endorphin Changes after Bruce Test in
Active and Sedentary Individuals
Parichehr Hanachi1*, Parvaneh Nazarali2, Roghyeh Ciyabi2
1Biochemistry Unite, Biology Department, Faculty of Basic Science, Alzahra University, Tehran, Iran
2Physiology Department, Faculty of Sport Science, Alzahra University, Tehran, Iran
Email: *
Received May 30th, 2012; revised June 30th, 2012; accepted July 14th, 2012
Opioid peptides have been implicated in many biological processes acting as hormones, neurohormones
or neurotransmitters. The aim of this research was to investigate effect of endurance training on plasma
beta endorphin (BA) changes in active and sedentary girls. 12 healthy physical education students as active
group (n = 12, active group with, 21.6 ± 0.6 year age, 162.25 ± 3.68 cm in height, and 54.13 ± 6.35 kg,
weight) and 12 healthy non physical education as sedentary group (n = 12, sedentary group, age 20.55 ±
0.69 year, high, 161.40 ± 3.14 cm, weight, 59.25 ± 4.45 kg) requited. Subjects entered the study on their
usual diet and after familiarization with training protocol, Bruce test (treadmill test) as aerobic test applied.
The blood sample was collected before and after training in both groups. Beta-endorphin concentration
was determined by radioimmunoassay kits. The analyses and data processing showed that there is no sig-
nificant difference within active (0.77 ± 0.1 pmol/l) and sedentary group (0.82 ± 0.01 pmol/l) in basal BE
at rest. The BE levels after endurance training in active group and sedentary group increase respectively
(0.83 ± 0.09 pmol/l), (compared with basal) however, significant difference was found between pre and
post test group in active group (P > 0.05). In this research, BE secretion increased in response to endur-
ance exercise both in active and sedentary girls.
Keywords: Beta Endorphin; Treadmill Test; Endurance Training; Active; Sedentary
Endogenous opioid peptides constitute a flexible and wide-
spread regulatory modulatory system. Opioid peptides have been
implicated in many biological processes acting as hormones,
neurohormones or neurotransmitters. Their influence is medi-
ated by specific opioid receptors. Three classes of endogenous
opioid peptides can be discriminated between: Enkephalins, En-
dorphins and Dynorphines (Hackney, 2006). Enkephalines are
found mainly in brain. In this tissue methione and leucine en-
kephalins (met- and leu-enkephalins) are purified and charac-
terized. None is very potent because of their rapid enzymatic
degradation. Met-enkephalin is also found in the blood plasma
and in a relatively high concentration in comparison with other
opioid peptides (Angelo et al., 2001). The circulating met-enke-
phalin is in a several fold molar excess over the circulating
endorphin. An extremely high concentration of enkephalins is
co-localized and co-released with catecholamines in adrenal me-
dulla. In this connection the met-enkephalin concentrations in
the adrenal vein is higher than in other parts of the circulation.
However the majority of the circulation met-enkephalin origin-
nates in the sympathetic nervous system (Bender et al., 2007;
Pierce et al., 1993).
Dynorphins are extended forms of leu-enkephalins. They are
among highly potent opioid peptides. The dynorphin family in-
cludes dynorphin A, dynorphin B, and neo-endorphin. A com-
mon precursor for endorphins and pituitary corticotropin, as well
as for β-lipotropin, β-melanotropin and probably also for met-
enkephalin is pro-opiomelanocortin (Farrel, 1998; Kraemer et
al., 1993).
Opioid peptides activate three different types of receptors;
mu, kappa and delta receptors, all of which act through a sec-
ond messenger (Andrea, 2006; Tamas et al., 2007).
Endorphins (endogenous morphines) are produced in various
brain structures, with the highest rate in the arculate nucleus of
the hypothalamus. The endorphin is synthesized in the hypophy-
sis and adrenals. It is not excluded that there are other sites.
However, the main source of blood endorphins is the hypophy-
sis. Endorphins primarily operate via the mu receptor. This re-
ceptor is known to mediate analgesic effects as well as play a
role in the reward system within the brain. Evidence showing
that endorphins can interfere with the release of other neuro-
transmitters, including norepinephrine, dopamine, and acetyl-
choline, have led to a belief that they work by modulating the
presynaptic membranes of synapses other than own (Tamas et
al., 2007; Goldfarb et al., 1997) The main opioid peptide is beta
endorphin. Products of its metabolic degradation are alpha and
gama endorphins.
The production of endorphins is stimulated by a hypotha-
lamic neuropeptide, corticoliberine. It acts via corticoliberine
receptors located in the hypophysis as well as in various nerv-
ous structures. In the hypophysis the result of the activity of
corticoliberine receptors is the formation from pro-opiomelano-
cortin of corticotropin, β-endorphin and β-lipotropin, as well as
the secretion of these substances into the circulation. The re-
sulting increase in the corticotrophin and β-endorphin blood
levels is rather parallel after endogenous administration of cor-
ticoliberine or under the influence of various stressors.
Blood-borne endorphins do not gain entry into the central
*Corresponding author.
nervous system. They actualize their regulatory/modulators func-
tion through peripheral receptor sites. Only a limited amount of
blood endorphins can reach neural receptors in sites not pro-
tected by the blood-brain barrier. Anyway, there are two dis-
crete parts of the endogenous opioid system: central nervous
and peripheral parts. The activities of these two parts may be in
good correlation, but the produced opioids are not transferred
from one compartment into the other. However, met-enkephalin
and dynorphin may cross the blood-brain barrier using an allos-
terically modulated saturable transport mechanism (Gorostiaga
et al., 2004; Taylor et al., 2000).
In order to establish the physiological function of endoge-
nous opioids, an opioid receptor antagonist, naloxane, is widely
used. In this way their role has been indicated in decreased pain
perception, suppression of affective disorders, promotion of
learning and memory, hunger and thirst influence, glucose ho-
meostasis, regulation of cardiovascular functions, respiration,
endocrine activities, renal function, gastrointestinal activity, lym-
phatic function/immunity, and sexual behavior as well as ther-
mal regulation.
The euphoric feelings generated by endorphins which may
result from strenuous exercise, are believed to play an impor-
tant role in addiction (Goldfarb et al., 1997; Farrel, 1998; Gor-
ostiaga et al., 2004; Anthony et al., 2006; Hegadon et al., 2009;
Courteny et al., 2004). While it is generally accepted that en-
dorphins induce euphoria, it is unclear whether exercise causes
an increase in endorphin levels (Armstrong, 2006). Addition-
ally, if exercise increases endorphin levels, few studies have
been performed to measure whether this increase plays a role in
exercise dependence. Because findings of endorphin elevations
are so inconsistent, researchers continually alter experimental
strategies. Unfortunately, this makes it difficult to determine
what, if any, strategies effectively measure endorphin and the
physiological response to exercise. Based on different research,
it appears that endorphin activity may be highly variable from
one individual to the next, making this analysis even more com-
plex (Taylor et al., 2000). Many researches have not found
significantly elevated endorphin levels after exercise (Heitkamp
et al., 1998; Harbach et al., 2000).
Farrell (1985) assessed the threshold by looking at the effects
of intensity and distance of running on endorphin release in male
subjects by compiling results from multiple studies with varied
time and distance of running. Analyses of these data indicated a
trend of elevated endorphin levels after exercise in all studies,
although not all were significant. Pierce et al. (1993) performed
a study measuring plasma endorphin levels before and after
endurance exercise, 45 minutes of high intensity aerobics. Re-
sults indicate a significant increase in endorphin levels after the
exercise while compared to levels before. These findings sup-
port the idea that opioid peptides may be released as a result of
exercising vigorously for a specific amount of time. A study by
Goldfarb et al., (1997) agrees with the conclusion, but claims
that a critical intensity of exercise must be attained to induce
elevation in plasma endorphin levels. However, contrary to the
data by Goldfarb et al., (1997), Farrell’s (1985) evidence shows
that the increase in endorphin release did not appear to be de-
pendent on the intensity of running.
While much data has been published about the relationship
between endorphins and intensity of the exercise, other researches
tested different forms of exercise, mostly the different between
running and bicycling. In fact Pierce et al. (1994) asserted that a
70% VO is required to significantly elevate endorphin levels in
the blood plasma.
All these studies demonstrate a variety of measurements on
human participants examining endorphin activity. Non indicate
strong evidence of increase of endorphin level release at a result
of vigorous exercise, although many suggest trend such a re-
sponse. This trend is enough to compel researchers to continu-
ally question if such a response exists.
So the aim of this research was to study changes of plasma
beta endorphin in response to endurance training in active and
sedentary girls.
Sixty volunteer female students in Alzahra University, Te-
hran Iran, were taken into the study. All subjects were asked to
complete a physical activity, medical examination and a medical
questionnaire to ensure that they were not taking any medica-
tion and free of endocrine or metabolic diseases. Menstrual cycle
was controlled and all the girls were in luteal phase to reduce
any side effect.
Calculated body mass index (BMI) (kg/m2) and waist hip ra-
tio (WHR) were measured to analyses anthropometry factors in
two groups. Waist circumference was measured in a horizontal
plane at the level of natural waist that was the narrowest part of
the torso. Hip circumference was measured at the largest pro-
trusion of the buttock without compressing the skin (Latifah &
Hanachi, 2008).
Finally 12 healthy physical education students as active group
(21.6 ± 0.6 year, 162.25 ± 3.68 cm, 54.13 ± 6.35 kg) and 12
healthy non physical education as sedentary group (20.55 ±
0.69 year, 161.40 ± 5.14 cm, 59.25 ± 6.45 kg) were studied
during a medical check up in order to measure their exercise
induced plasma beta endorphin responses. All students in active
group were following their regular university sport programs,
but were not involve vigorous and high intensity physical train-
ing. Non were receiving medication at the time of the study. The
training protocols acquainted to participants and inform consent
was obtained from all subjects. The anthropometrical charac-
teristics of active and sedentary groups were shown in Table 1.
Exercise Test
Bruce test (treadmill test) was exerted as endurance training
which had 10 steps with duration of 3 minutes in each steps.
The protocol of this test mentioned below in Table 2. Then
subjects warm up for 5 minutes and start doing (treadmill test)
protocol (Bruce et al., 1994). The test finished when subjects
could not continue the training sections. Prior to experimental
Table 1.
Mean values of anthropometric characteristics of active and sedentary
Sedentary group (n = 12) Active group (n = 12)
Age (year)20.55 ± 0.69 21.67 ± 0.65
Height (cm)161.40 ± 5.14 162.25 ± 3.68
Weight (kg)59.25 ± 6.45 54.13 ± 6.35
BMI (kg/m2)21.89 ± 2.40 20.52 ± 2.23
WHR 0.83 ± 0.04 0.80 ± 0.02
Copyright © 2012 SciRes.
trial, a flexible catheter was placed into an antecubital right hand
vein and two blood samples were collected in resting period
and after the training. The serum beta endorphin levels meas-
ured in both active and sedentary groups (Figure 1).
Serum Beta Endorphin Levels
Venous blood samples from the right hand arm of the sub-
jects were taken to measure levels of beta-endorphin before and
immediately after specialized training protocol under stress-free
condition, as possible.
Serum blood samples immediately were centrifuged at 5000
rpm for 10 min at 4˚C and serum were stored at –70˚C until beta
endorphin assayed. serum level of Beta-endorphin was deter-
mined with standard radioimmunoassay kit (Phonix Pharmaceu-
ticals, Inc., California, USA) with high affinity for beta endor-
phin and cross reactivity of less than 6.2% for B-lipotropin levels
and less than 0.01% for other peptides.
Statistical Analysis
The statistical analyses were performed with the SPSS 17 for
Windows program. The differences between groups and between
values before and after each group were calculated as mean ±
standard deviation. Independent samples t-test were used in the
statistical analyses. P < 0.05 was considered to be statistically
Table 2.
The experimental protocol of Bruce test.
Step Time (min) Speed (km/hr) Gradient
1 0 2.74 10%
2 3 4.02 12%
3 6 5.47 14%
4 9 6.76 16%
5 12 8.05 18%
6 15 8.85 20%
7 18 9.65 22%
8 21 10.42 24%
9 24 11.26 26%
10 27 12.07 28%
ActivegroupSede ntarygroup
Prete st
Postte s t
Be t aendorphin(pmol/l)
Figure 1.
Beta endorphin levels (pmol/l) before and after Bruce test as an endur-
ance training protocol in active and sedentary group. Data were mean ±
S.E.M. *Statistical significance was accepted at P 0.05.
The analyses and data processing showed that there is no
significant difference within active (0.77 ± 0.1 pmol/l) and sed-
entary group (0.82 ± 0.01 pmol/l) in basal BE at rest. BE levels
after endurance training in active group and sedentary group
increase respectively (0.83 ± 0.09 pmol/l), (compared with basal)
however, significant difference was found between pre and post
test group in active group (P > 0.05). The increase in beta en-
dorphin in active group after endurance training was higher
than sedentary group (Figure 1).
Discussion of Findings and Recommendations
The hormonal changes can have important effect on physical
activity functions. In particular, exercise leads to the release of
certain neurotransmitters in the brain that alleviate pain, both
physical and mental. Much of the research done in this area has
focused on running, but all types of aerobic exercise provide
benefits. Although the exact nature of these benefits is still being
determined, enough research has been done to provide even skep-
tics with a motivation to take up exercise. Exercise exerts its ef-
fects on the brain through several mechanisms, including neu-
rogenesis, mood enhancement, and endorphin release (Andrea,
Exercise-induced increases in the peripheral beta-endorphin
concentration and mainly associated both with changes in pain
perception and mood state. A more precise understanding of
opioid function during exercise can be achieved by investigat-
ing the changes in beta-endorphin concentrations dependent upon
intensity and duration of physical exercise and in comparison to
other stress hormones. Published studies reveal that incremental
graded and short term anaerobic exercise leads to an increase in
beta-endorphin levels, the extent correlating with the lactate
concentration (Goldfarb et al., 1997; Armstrong, 2006).
Many studies have examined the relationship between exer-
cise and endorphin release, studying the role of these peptides
in exercise induce euphoria as well as the reduction of pain
(Farrel, 1998; Bouix et al., 1993; Fry et al., 1997).
All these studies demonstrate a variety of measurements on
human participants examining endorphin activity. Non indicate
strong evidence of increase of endorphin level release at a result
of vigorous exercise, although many suggest trend such a response.
In this study the result showed that the levels of plasma beta
endorphin increases after exercises both in active and sedentary
groups. It could be related to physical stress produced by long
distance running. Other possible functions of beta endorphin
increase could be related to the endocrine response to exercise,
because a role in glucorticoid release and energy balance (An-
thony et al., 2006). It is possible that the release of beta endor-
phin is linked to other functions that must be controlled during
the practice of exercise, as are antihypertensive mechanisms,
respiratory response and immuno response. However, further
studies at biochemical and physiological levels are necessary in
order to elucidate the role played by B-end release during physic-
cal exercise. The main finding of this study was that experi-
mental inconsistence makes it nearly impossible to draw a dis-
tinct relationship between exercise and elevation in endorphin
blood plasma levels. Therefore further investigations are nec-
essary to determine the role of beta-endorphin in exercise-med-
iated physiological and psychological events.
Copyright © 2012 SciRes. 101
Copyright © 2012 SciRes.
The authors would like to thanks the Faculty of Sport Sci-
ences, Alzahra University, Tehran, Iran, for funding this study.
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