The Effect of Endurance Training on the Ratio of Serum Cortisol to

International Journal of Basic Sciences & Applied Research. Vol., 4(1), 38-43, 2015
Available online at http://www.isicenter.org
ISSN 2147-3749 ©2015
The Effect of Endurance Training on the Ratio of Serum Cortisol to
Dehydroepiandrosterone (DHEA) in Inactive Young Women
Somayeh Mahdaviyan1*, Laleh Behboodi1, Mojtaba Ezadi2
1
Department of Physical Education, Islamic Azad University, Islamshahr Branch, Tehran, Iran
Department of Sports Sciences and Physical Education, Saveh Branch, Islamic Azad University, Saveh, Iran
2
*
Corresponding Author Email: rauf1998@yahoo.com
Abstract
The aim of present study was to determine the effect of endurance training on
balance of anabolic to catabolic in inactive young woman's body (Ponjee, 1994).
Inactive young woman aged 24.50 ± 2.653 years, height 164.64 ± 5.624 cm,
weight 57.928 ± 4.921 kg, body mass index (BMI) 21.376±1.031 kg by the square
of height the meter, selected through purposive convenience sampling and
randomly divided into exercise and control groups (each group, n=10). Practice
group participated at 8 weeks of endurance training for 3 days a week with
highly increasing and the control group did not follow any regular physical
activity, and only performed the normal and routine activities. Before and after
training, was taken blood samples from subjects of and measured and
calculated cortisol, DHEA and ratio of serum cortisol to DHEA. T-test used for
comparison of variables. Cortisol in the exercise group compared with the
control group was significantly increased (P<0.05). Also the rate of DHEA and
ratio of serum cortisol to DHEA in the exercise group compared with the
control group significantly decreased. 8-week endurance training similar to the
present protocol providing a catabolic environment in the body of the inactive
young women. However, it appears that the results of this study is due to the
overtraining, and besides the psychological and physiological condition of
regnant the subjects may be according to the protocol of exercises, apply high
training intensity in the final weeks of exercise, especially for those who were
disabled before it can be considered overtraining.
Keywords: Endurance training, Ratio of DHEA to cortisol, DHEA, Serum cortisol.
Introduction
One of the most important methods for evaluating the intensity of the exercise and its effect on athletes is measure
biochemical variables, In this regard, biochemical variables can be divided into three general categories of enzymes,
hormones and metabolites. Among the hormones more concerned to anabolic and catabolic hormones, if so that
catabolic hormones increase subsequent exercise was signs of high pressure of activity or if the balance be established
between anabolic and catabolic hormones athlete is in good fitness condition. In this regard, testosterone and cortisol
hormones to order as anabolic and catabolic hormones are considered more than others hormones and the ratio of these
hormones is another useful indicator for determining the condition and pressure of work and training (Obminski, 1997).
Endurance training attention too many of people, especially women. This exercise causes physiological changes and
adaptations that most of it can be found in the neuromuscular system and hormones. Measuring the indexes of pressure
of practice followed by various training programs can contribute to a better understanding of the acute and chronic
effects of endurance training. For this purpose, in men used testosterone to cortisol ratio and said that if this ratio
decrease 30% or greater, indicate that overtraining syndrome, But in women because of this hormone secreted by the
ovaries and adrenal gland being used from another anabolic hormone that is the precursor of testosterone and called
DHEA. So in women DHEA to cortisol ratio as an indicator of exercise pressure (Urhausen, 1995). In this circumstance
the level of cortisol is dramatically increased that due to exercise stress, lack of adequate rest and nutrition
inappropriate, and it is well known energy reserves are not recovering well and retrieved, and in the next training athlete
38
Intl. J. Basic. Sci. Appl. Res. Vol., 4(1), 38-43, 2015
earlier exhausted and function is impaired (Obminski, 1997). Now, if athlete after exercise, has enough rest or good
nutrition lower this ratio decreases. On the other hand athlete who suddenly increase his exercise volume and intensity,
exposure decrease of ratio. Recently endurance training take into consideration by many of women that has effects for
health and fitness. If the exercise pressure was excess capacity of physiological not only improve performance but
impair the performance, and puts a person under the effects of overtraining. On the other hand, if the exercise pressure
was low, is not created significant improvements in performance and physiological adaptations.
Methodology
Subjects
The population of this research were consisted of all inactive healthy girl student of Azad University of Tehran
center (20 to 28 years old). Recall over 20 person have declared their readiness to participate in research. The number of
20 inactive student girls (20 to 28 years old) 24.50 ± 2.653 years, height 164.64 ± 5.624 cm, weight: 57.928 ± 4.921 kg
and body mass index (BMI) 21.376) ± 1.031 kg per cubic meter, selected through purposive convenience sampling and
randomly divided into exercise and control groups (each group, n = 10). All subjects had a complete physical health
(physician confirmation). Researcher with subjects Homogenization (exception genetic material), reduce probability of
influence disruptive variables on dependent variables. Demographic characteristics of the subjects are presented in
Table 1. Subject of two groups were similar in terms of age, height, weight and BMI (P> 0.05).
Table 1. Demographic characteristics of subjects.
Group
Exercise
Control
Total
Age
2.636±24.571
24.428±2.878
2.653±24.50
Height
4.790±165.43
163.86±6.644
5.624±164.64
Weight
58.571±5.503
57.285±4.608
4.921±57.928
BMI
21.412±1.488
21.34±0.295
21.376±1.031
Methods of data collection
One week before run study, subjects were familiar with exercise protocol in justification meeting. Also the
personal and demographic characteristics of the subjects were measured. Then, were taken blood samples, 48 hours
before the start of the test in the fasting state, the subjects conducted their exercise program for 8 weeks increasingly. At
this time the control group did not perform any physical activity and sport, and only do their daily activities. After
completing the 8 weeks of training, and after the proportional rest with gap of first day of sampling and the start of
training (48 hours), second test session done like to first test and obtained rest blood samples in the fasting status.
Exercise program
Endurance training was consisted of 8 weeks and 3 days each week. A percentage of maximum heart rate and
duration of exercise was considered as intensity and volume of training. Each run session was 35 minutes including a 5
minute warm up, 25 minutes main exercise and 5 minutes cool-down? 25 minutes of main exercise was include running
on the treadmill. For first to eight weeks done with 60%, 65%, 70%, 70%, 75%, 75%, 80% and 85% of maximum of
heart rate. To display the heart rate on the treadmill screen was used the belt. Each subject started and finished all
activities meetings at own time, that this time were the same for all. Hormonal analysis: 48 hours before and 48 hours
after training, were collected blood sample of subjects of both groups from central venous at a rate of 5 ml. It should be
noted that after each session, participants were considered to drink enough fluids to compensate for lost fluid.
Blood samples was poured in sterile tubes containing K3EDTA, heparin and EDTA tubes were placed in ice and
then for a few minutes left at room temperature, followed by centrifugation was separated serum from plasma for 10
minutes at around 3500 RPM. All blood samples were kept to be frozen at -20 ° C until to reach the laboratory, and
there began laboratory test immediately. Serum cortisol level was measured for each sample from using the ELISA way
and IBL kit with sensitivity of 2.5 ng ml, also DHEA was measured for each sample from using the ELISA way and
IBL kit with sensitivity of 0.108 ng ml. To calculate the ratio of cortisol to dehydroepiandrosterone, after the conversion
of unit of both hormone to nanomole per liter and also was used to formula of ng/ml * 275.9 = nmol/l for conversion
unit of cortisol and formula of ng/ml * 3.47 = nmol/l for conversion unit of dehydroepiandrosterone. Statistical
Methods: First the variables were described with the mean and standard deviation. Then was used Smirnov Kolmogorov test for the determine of normal distribution and license to use the parametric or non-parametric tests. Also
was used paired t-test to investigate the changes of variables in the exercise and control groups, also was used
independent t-test in order compared to the values of each variables between the exercise and control groups. For all
statistical tests was set the significance level equal to 0.05, also was used the statistical software SPSS version 16 for
statistical calculations.
39
Intl. J. Basic. Sci. Appl. Res. Vol., 4(1), 38-43, 2015
Results
Statistical description of the variables is presented in table 2. Results of dependent and independent t-test
(respectively to assess intragroup and intergroup comparisons of variables) are presented in tables 2 and 3. Weight and
BMI decreased in the exercise group compared with the control group (P <0.05). Cortisol increased in the exercise
group compared with the control group (P <0.05). DHEA and DHEA to cortisol ratio also decreased in the exercise
group compared with the control group (P> 0.05).
Table 2. Mean and standard deviation of variables.
Variables
Groups
Training
Control
Training
Control
Training
Control
Training
Control
Training
Control
Weight (kg)
BMI (kg/m2)
Cortisol (ng/ml)
DHEA (ng/ml)
DHEA to Cortisol Ratio
Pre
58.571±5.503
57.285±4.608
21.412±1.488
21.34±0.295
29.072±26.153
19.407±8.884
92.228±18.286
100.23±19.144
5.950±6.005
6.434±3.414
Post
54.428±5.912
57±4.932
19.870±1.363
21.230±0.557
31.837±26.837
19.45±8.988
85.157±16.411
100.57±20.562
4.474±3.928
6.524±3.702
Table 3. Results of t-tests to examine within-group variables.
Variables
Weight (kg)
BMI(kg/m2)
Cortisol (ng/ml)
DHEA (ng/ml)
DHEA to Cortisol Ratio
Groups
Training
Control
Training
Control
Training
Control
Training
Control
Training
Control
t
6.96
0.67
6.28
0.67
10.71
1.96
5.19
1.29
11.06
2.28
df
9
9
9
9
9
9
9
9
9
9
Sig.
0.000 *
0.52
0.001 *
0.52
0.000 *
0.08
0.001 *
0.22
0.000 *
0.04 *
* Significant in P≤0.05
Table 4. Results of t-test for comparison between groups of variables.
Variables
Weight (kg)
BMI(kg/m2)
Cortisol (ng/ml)
DHEA (ng/ml)
DHEA to Cortisol Ratio
* Significant in P≤0.05
∆: Changes before and after exercise
40
Groups
Before
After
∆
Before
After
∆
Before
After
∆
Before
After
∆
Before
After
∆
t
0.47
0.88
5.29
0.12
2.44
5.04
1.47
2.27
6.93
0.52
2.43
3.01
3.46
2.07
5.89
df
12
12
12
12
12
12
12
12
12
12
12
12
12
12
12
Sig.
0.64
0.39
0.000 *
0.90
0.03 *
0.000 *
0.15
0.03 *
0.000 *
0.61
0.02 *
0.007 *
0.003 *
0.053
0.000 *
Intl. J. Basic. Sci. Appl. Res. Vol., 4(1), 38-43, 2015
Discussion and Conclusion
Based on research findings, endurance training caused to increase serum cortisol levels significantly. In line with
the findings of this present, Hossieni et al (2009), also reported cortisol increases in the endurance training group, but
the Aghaalinejad et al (2013) showed that when resistance training implemented as endurance and consistently training,
can reduce serum cortisol in young women during 8 weeks. Also in Hiruntrakul and Ratanavadee (2010), showed
cortisol levels of rest had not significant difference between endurance training and control groups, they concluded that
12 weeks of moderate-intensity and low repetition don have effect on cortisol in inactive people. In Hejazi and
Attarzadeh Hosseini (2010) Thirteen elite male runners participated in a semi-endurance exercise program consisted of
14 weeks and 12 sessions per week (morning and afternoon), blood samples were collected in three stages, before
preparation, after preparations and before the competition.
Cortisol decreased significantly in the after stage of preparation, although increased in stage of before
competition. Unlike the present findings, Chatard (2002) reported that non-athletes are more cortisol concentration than
athletes in rest. Different results may be due to differences in the exercise protocols. The present results suggest that
exercise increases resting cortisol levels. The researchers stated that Cortisol has stressful role as a hormone, due to
hypothalamic-pituitary-adrenal axis stop will be used as a valid indicator for the diagnosis of overtraining and
prevention of mental increasing activities acquired of the tournaments. Two factors, intensity and duration of exercise
change the response of the adrenal pituitary-hypothalamic axis to exercise. It’s possible in the study that training
intensity up to 80 or 85% has partly caused overtraining in maximum rate at end session.
Recent studies have shown that it is better to practice with a uniform intensity in the final weeks of rehearsal as
the last 3 or 4 weeks and impose additional burden not done with higher intensity in sessions before the sampling, so
this leads to some kind of consistency. Other factors that alter the cortisol response to exercise include Hyper
Hydration, food and the circadian rhythm. Physiological loads (intensity and volume) non-proportional and intensities
exercise leads to increase cortisol due to raising the secretion of the adrenocorticotropic hormone that is a response to
increased susceptibility to stress on the hypothalamic-pituitary-adrenal axis.
Different workloads (intensity and volume) different exercises (strength, endurance, power) micro cycle training
courses, macro cycle and individual compatibility show different hormonal responses. Since the present study showed
an increase in cortisol, it can probably be due to the incompatibility of the hypothalamic - pituitary-adrenal axis to
training conditions and lack of lowering cortisol sensitive and lack of sensitivity change of tissue to the cortisol. On the
other hand, the results suggest that physical activity cause increasing the levels of releasing hormone of catecholamines
and cortisol .
 The time of increasing or their achieving to a base level is not same on the all of them. Some of them, such as
cortisol unlike the catecholamines have slower fluctuations will affect the physiology of the body for a few days.
 Based on the results of this study, slow drop of cortisol which lasts for several days is one possible reason for the
increase in cortisol levels.
This means that if the second sampling was performed 72 hours after the last training session insteade of 48 hours
after the last session, this result was not gained because disabled people spend a longer recovery period than active
people. Exercise load presented in this study for an ordinary athlete and for a normal and non-active person may be too
according to the principle of individual differences. Therefore, based on the findings of overtraining can effect on
anabolic and catabolic steroids such as cortisol (Khaledan, 2002). Some studies have considered the performance.
However, there are conflicting results in this area and as mentioned above, it can be related to the nature of the sport,
the exercise volume and intensity, measurement interval, subjects, the sampling manner( blood, saliva )and the
willingness of individuals(Engelmann, 2004).
Numerous studies have been conducted on factors of hormones overtraining, and overtrainings has caused an
increasing IL-6 and this leads to increase lipolysis and thus it stimulates cortisol and other cytokines (Asgarpour &
Nazarali, 2012). In the present study, lose weight and body mass index may also show an increase in IL 6 which is not
measured. Researchers have expressed that the lack of hormonal changes may be the result of appropriate and normal
exercises with proper recovery thereby cause to maintain the stability the hypothalamic-pituitary axis. Thus the
appropriate recovery allows adaptation to stress that occurs during the stress response (Halson & Jeukendrup, 2004).
However, the increase in cortisol in this study may come from the improper training or lack of proper recovery for this
group. Based on research findings, one endurance training period significantly reduce the levels of DHEA of serum.
Hosseini et al (2009) also reported a decrease in DHEA in the endurance training group.
In contrast, Sato (2013) reported that DHEA levels, 5 alpha Dihydrotestosterone and5-alpha reductase
Dihydroergotamine were significantly higher in skeletal muscle of diabetic rats after 6 weeks in exercise group. Also
Johansson and Lars-Eric (2013) reported that the DHEA sulfate and the ratio of DHEA sulfate to cortisol were
significantly higher than in amateur hockey players to professional hockey athletes but it was not like this in the case of
cortisol. Aghaalinejad (2013) in their study reported an increasing the DHEA serum of young women during 8 weeks.
In Hiruntrakul and Ratanavadee (2010), resting levels of total testosterone and free testosterone showed no significant
difference between the two endurance training and control groups. They concluded that 12 weeks of exercising with
moderate-intensity and low repetition have no effect on testosterone of disabled people. In Hejazi and Attarzadeh
41
Intl. J. Basic. Sci. Appl. Res. Vol., 4(1), 38-43, 2015
Hosseini (2010) testosterone after preparation and before the non-compete period was increased and decreased,
respectively.
Hakkinen and Pakarinen (2005), showed respectively, after 12 and 21 weeks of strength and endurance training
observed the increasing the amount of saliva di DHEA on disabled women. Arce and De Souza (1993) found that
subjects of endurance and resistance training have lower levels of testosterone than control group. In contrast to the
present findings, Keizer (1989) reported that the DHEA sulfate dioxide increases in response to endurance exercise.
Important characteristic of overtraining syndrome has listed reduction of function as a result of an imbalance between
anabolic and catabolic hormones with dysfunction in the hypothalamus-pituitary-adrenal axis.The role of testosterone
as an anabolic hormone, and cortisol is important as a catabolic hormone. Testosterone on hypertrophy muscle and
muscle glycogen synthesis is important and indicates the anabolic state in the body. According to the researchers’
results, the long-term exercises increase plasma cortisol levels and reduce their testosterone (Hakkinen & Pakarinen,
2005; Arce & De Souza, 1993; Keizer, 1989). Perhaps the time of practice of the present study was also long to prepare
participants. DHEA of blood can turn to Androstenedione, which can then be converted to testosterone. Researchers
have considered reduction of testosterone levels in the blood a key indicator of fatigue and overtraining (Katsuji, 2010;
Ponjee, 1994). Resting testosterone affected by several factors such as exercise varies (duration and intensity),
individual characteristics (age, sex) and diet. Testosterone reduction after exercise induced increases in intensity,
duration, repeat action the exercise load that do not give the opportunities to restoration and reset (Platen, 2002).
Testosterone levels can also reduce followed by intense endurance exercise and resistance exercise and
particularly when is associated with dietary restriction and negative energy balance (Engelmann et al., 2004). In the
present study the weight reduction and BMI of negative energy balance caused by diet may also not be controlled.
Mechanisms of reduction of testosterone levels may be because of gonad releasing hormone secreted by the
hypothalamus, prolactin increasing and inhibition of by the LH hormones secreted of pituitary or directly inhibition by
cortisol (Halson & Jeukendrup, 2004). Also increase in testosterone levels is mainly depends on the done work load,
involved muscle mass, and rest between repetitions and athletes preparation (Viru, 2005; Kraemer, 1988) said resting
concentration of testosterone levels may be a reflection of the current state of muscle tissue and whether establish the
anabolic conditions or not. In this present study also levels of DHEA reduced. This issue could be indicative of
catabolic conditions.
The results demonstrate that this reduction may relate to non-adjusted for action on the hypothalamic-pituitary
axis on the adrenal and ovary in response to the balance between the exercise activity and recovery or intensity and
volume of exercise (Pederson, 2000). On the other hand, DHEA has been used empirically in patients with depression
and has been successful in improving depression and memory. So regard to non- control the psychological conditions of
subjects may have changed estrogen rates due to mental conditions. Based on research findings, one endurance training
course significantly reduced levels of (DHEA) compared to serum cortisol. Hosseini et al (2009) also reported the
increase in de (DHEA) to cortisol in the endurance training group.
Johansson and Lars-Eric (2013) reported that the sulfate of (DHEA) and ratioof DHEA sulfate to cortisol was
significantly higher in amateur hockey players to professional hockey players. Aghaalinejad (2013) in their study
demonstrated an increase ratio of DHEA to serum cortisol during the 8 weeks. Hejazi and Attarzadeh Hosseini (2010)
showed that the testosterone has significantly increase compared to cortisol. Consistent with our findings, Ponjee (1994)
also has reported a significant decrease in DHEA and cortisol after long-term endurance activities. DHEA ratio to
cortisol is used as a marker of training stress in athletes. This ratio is influenced by the intensity and duration of
exercise, any change in this ratio can be associated with a probably change in immune function (Hossieni &
Aghaalinejad, 2009). Research shows that DHEA ratio reduced to cortisol, in the individuals who are suffering from
overtraining (Halson & Jeukendrup, 2004; Moore & Fry, 2007).
In this study, we observed a significant decrease in the ratio of these two hormones in the control and
experimental groups. This decrease reflects the imbalance of the anabolic/catabolic and creating conditions of catabolic
in the training phase of the research group. Mainly different in the various results may be due to differences in the type
of training and the individual's physical and psychological characteristics. The results show a lack of adaptation of
overtraining to the stress, training conditions and are a sign of an appropriate return to its original state and fatiguecausing factors (Hayes et al., 2010). It can also be stated since the subjects in this study(inactive women)has low
preparation levels, changes in the measured parameters affect by exercise can probably be attributed to their low fitness,
perhaps the exercise protocol in individual with better fitness will lead to overtraining.
Based on research findings, such it can be concluded that the 8-week endurance training creates a catabolic
environment in the non-active young woman's body and this practice can lead to weight loss due to hormonal changes
and are useful for people who need to lose weight. But it seems the results of the research indicate overtraining and
furthermore, physiological and psychological conditions of the study may be considered a form of overtraining
according to the exercise protocol of implying increase the training intensity in end weeks especially for those who
have already inactive. On the other hand, Cortisol, unlike Catecholamines has the slower fluctuations and will affect the
physiology of the body for a few days. Such an outcome was not achieved if the sampling at 72 h was performed after
the last training session instead of the second sampling which was performed at 48 h after the last session.
42
Intl. J. Basic. Sci. Appl. Res. Vol., 4(1), 38-43, 2015
References
Agha-Alinejad H, Kohanpour MA, 2013. Effects of resistance training on serum cortisol and dehydroepiandrosterone
levels in trained young women. Iranian Journal of Pathology. 8(1): 9–16.
Arce JC, De Souza MJ, 1993. Subclinical alterations in hormone and semen profile in athletes. Fertil Steril. 59: 398404.
Asgarpour S, Nazarali P, 2012. Relationship between IL-6 concentration after a short period of intensive training and
overtraining in elite female athletes. Sport Physilogy J. 16: 41-52.
Chatard JC, Atlaoui D, Lac G, Duclos M, Hooper S, Mackinnon L, 2002. Cortisol, DHEA, performance and training in
elite swimmers. Int J Sports Med. 23(7): 510-15.
Engelmann M, Landgraf R, Wotjak CT, 2004. The hypothalamic-neurohypophysial system regulates the hypothalamicpituitary-adrenal axis under stress: an old concept revisited. Frontiers in neuroendocrinology. 25(3): 132-149.
Hakkinen A, Pakarinen A, 2005. Effects of prolonged combined strength and endurance training on physical fitness,
body composition and serum hormones in women with rheumatoid arthritis and in healthy controls. Clin Exp
Rheumatol. 23(4): 505-512.
Halson SL, Jeukendrup AE, 2004. Does overtraining exist?: An analysis of overreaching and overtraining research.
Sports Medicine. 34(14): 967-981.
Hayes LD, Bickerstaff GF, Baker JS, 2010. Interactions of cortisol, testosterone, and resistance training: influence of
circadian rhythms. Chronobiology international. 27(4): 675-705.
Hejazi K, Attarzadeh Hosseini SR, 2010. Influence of selected exercise on serum immunoglobulin, testosterone and
cortisol in semi-endurance elite runners. Asian Journal of Sports Medicine. 3(3): 185-192.
Hiruntrakul A, Ratanavadee N, 2010. Effect of endurance exercise on resting testosterone levels in sedentary subjects.
Cent Eur J Public Health. 18(3): 169-172.
Hosseini M, Rostami R, 2009. Effects of strength and endurance training on serum immunoglobulin A, cortisol and
salivary DHEA in disabled girls. Journal of Babol University of Medical Sciences. 5: 38-44.
Hossieni M, Aghaalinejad H, 2009. Effects of aerobic exercise on serum IGA, cortisol, DHEA and DHEA: cortisol
ratio in untrained female. Iranian Journal of Endocrinology & Metabolism. 11(3): 293-299.
Johansson B, Lars-Eric U, 2013. Elite sport and biological age. Psychology J. 4(7): 613-618.
Katsuji A, Motoyuki I, Seiji Mc, 2010. Acute exercise activates local bioactive androgen metabolism in skeletal
muscle. Steroids J. 75: 219-223.
Keizer H, Janssen GM, Menheere P, Kranenburg G, 1989. Changes in basal plasma testosterone, cortisol, and
dehydroepiandrosterone sulfate in previously untrained males and females preparing for a marathon. Int J Sports
Med. 10(3): 139-145.
Khaledan A, Minansiyan V, 2002. Comparison of the biochemical and physiological changes in men over strength
training and endurance athletes. Harakat J. 5: 14-23.
Kraemer WJ, 1988. Endocrine responses to resistance exercise. Med Sci Sports Exercise. 20(5): 152-157.
Moore CA, Fry AC, 2007. Nonfunctional overreaching during off-season training for skill position players in collegiate
American football. J Strength Cond Res. 21(3): 793-800.
Obminski Z, Stupnicki R, 1997. Comparison of the testosterone-to- cortisol ratio values obtained from hormonal assays
in saliva and serum. J Sports Med Physical Fitness. 37(1): 50-55.
Pederson B, Hoffman k, 2000. Exercise and the immune system: regulation, integration, and adaptation. Physiol Rev.
80(3): 1055-1081.
Platen P, 2002. Overtraining and the endocrine system-Part 2. Review of the scientific studies. European Journal of
Sport Science. 2(1): 1-7.
Ponjee GA, Hans Rooya HA, Vader HL, 1994. Androgen turnover during marathon running. Med Sci Sport Exerc.
26(10): 1274-1277.
Sato K, Fujita S, 2013.The exercise-induced improvement in hyperglycemia is mediated by DHT produced in the
skeletal muscle of zucker diabetic fatty rats. J Diabetes Metab. 4: 239-247.
Urhausen A, Gabriel H, Kindermann W, 1995. Blood hormones as markers of training stress and over training. Sport
Med J. 20(4): 251-276.
Viru A, Viru M, 2005. Resistance exercise and testosterone. The endocrine system in sports and exercise. 56: 319-338.
43