• Users Online: 866
  • Home
  • Print this page
  • Email this page
Home About us Editorial board Ahead of print Current issue Search Archives Submit article Instructions Subscribe Contacts Login 


 
 Table of Contents  
ORIGINAL ARTICLE
Year : 2022  |  Volume : 7  |  Issue : 1  |  Page : 35-40

Effect of intense military exercise on physical proficiency and hormonal responses of soldiers: A pilot study


1 Department of Ergonomics, Defence Institute of Physiology and Allied Sciences, New Delhi, India
2 Department of Nutrition and Biochemistry, Defence Institute of Physiology and Allied Sciences, New Delhi, India

Date of Submission27-Jan-2021
Date of Decision10-Feb-2021
Date of Acceptance15-Feb-2021
Date of Web Publication27-Jun-2022

Correspondence Address:
Dr. Madhusudan Pal
Department of Ergonomics, Defence Institute of Physiology and Allied Sciences, Lucknow Road, Timarpur, New Delhi - 110 054
India
Login to access the Email id

Source of Support: None, Conflict of Interest: None


DOI: 10.4103/bjhs.bjhs_14_21

Rights and Permissions
  Abstract 


BACKGROUND: Military training activities are typically challenging and push the soldiers toward their maximum limits of capabilities to improve proficiency in real time situations. In terms of injury prevention, unit performance, and overall morale, the individual's physical capabilities must be in concert to the job demands. Hormones play an important role in regulating various physiological processes including fuel utilization by exercising muscles.
AIMS AND OBJECTIVES: This study was undertaken to quantify the hormonal demand of an intense military training event.
MATERIALS AND METHODS: The study was conducted at a military training center on 25 male healthy soldiers who had completed 11 week training. Venous blood samples were drawn before and immediately after the event.
RESULTS: In hormonal responses, the levels of epinephrine (P < 0.001), norepinephrine (P < 0.01), cortisol (P < 0.001), serotonin (P < 0.01), and aldosterone (P < 0.001) were significantly increased while testosterone (P < 0.001) was found significantly decreased after event. The present study demonstrated that the physical proficiency training activity was highly energy demanding due to significantly increased sympathoadrenergic responses and induced a high level of acute stress due to significant reduction of testosterone. In addition to this, the significantly increased serotonergic responses indicated that the level of fatigue was high during activity.
CONCLUSION: The findings of the present study may be helpful in screening of individuals before inducting into such intense military training activity to minimize the risk of injuries.

Keywords: Hormonal responses, military training event, physical proficiency


How to cite this article:
Yadav A, Arya K, Malhari A, Meena R, Chatterjee T, Bhattacharyya D, Singh SN, Pal M. Effect of intense military exercise on physical proficiency and hormonal responses of soldiers: A pilot study. BLDE Univ J Health Sci 2022;7:35-40

How to cite this URL:
Yadav A, Arya K, Malhari A, Meena R, Chatterjee T, Bhattacharyya D, Singh SN, Pal M. Effect of intense military exercise on physical proficiency and hormonal responses of soldiers: A pilot study. BLDE Univ J Health Sci [serial online] 2022 [cited 2022 Aug 16];7:35-40. Available from: https://www.bldeujournalhs.in/text.asp?2022/7/1/35/348283



Fitness requirements are mandatory for armed forces throughout the World. Training is a common method of preparing soldiers to be more resilient.[1] All soldiers are not equally capable of succeeding through and adapting to intense training at the same rate.[2] Exposure of various physical agents during combat training affects the performance and physical integrity of soldiers.[3] The mismatch of physical capability and demand of activity leads to high attrition in the least-fit soldiers.[4] Exercise tests are meant to train personnel progressively for improved endurance, reaction time, and coordination.[5] Therefore, quantification of physical fitness is critically important to know the buffering impact of stress.[6],[7]

Exercise is a form of physiological stress that requires hormonal and metabolic changes in order to adapt to disruptions in homeostasis.[8] Exercise-induced activation of the sympathetic nervous system results in increased production and secretion of epinephrine (Epi) and norepinephrine (NE) from the adrenal medulla and postganglionic neurons respectfully at the onset of exercise and continues to rise in an intensity and duration-dependent manner.[9],[10] High-intensity exercise leads to increase in plasma cortisol levels,[11] which is apparently required to cope with the higher energy demand.[12] It can be used as a biomarker to understand the level of stress exerted by high-intensity exercise. Exercise induces a significant loss of sodium and water through perspiration in a hot environment; this loss stimulates the renin–angiotensin–aldosterone axis.[13] During heavy exercise, the creatinine level increases due to muscle breakdown, high dehydration, reduction in renal blood flow, and glomerular filtration rate.[14] Therefore, the plasma level of aldosterone and creatinine quantification is necessary to understand the renal homeostasis of soldiers who underwent extreme military training activity. Testosterone is the gonadal anabolic hormone, which is extraordinarily sensitive to psychological stress and energy deficit with change in either direction depending on how the stressor is perceived.[15] A previous study said that the higher concentration of serotonin in the central nervous system (CNS) during exercise reflects more exertion and fatigue in participants.[16] Thus, the serotonin level in plasma plays an important role as a marker to understand the level of exertion and fatigue of soldiers undergoing intense activity. All together these hormonal and metabolic responses may be helpful in understanding the level of stress perceived during strenuous event.

It is very difficult to quantify the hormonal responses during real-time operations such as wars or peacekeeping missions.[17] Therefore, it is of utmost necessity to identify a kind of intense training activity similar to real-time conditions which can take the soldiers to their maximum level of resilience. Therefore, Physical Proficiency Test (PPT) activity was chosen to study the resilience level of soldiers. In this context, the present study was imperatively aimed to quantify the hormonal responses of soldiers undergoing the activity in order to depict the level of stress. It was intended to observe the impact of stress on resilience of soldiers during conduct of such intense activities.


  Materials and Methods Top


Study participants

Twenty-five healthy soldiers of SHAPE-1 standard as per Indian Army volunteered for this study. The characteristics of all the volunteers are represented in [Table 1]. Participants were well acclimatized to the study location 3 months before the commencement of the study. The participants wore t-shirt, shorts, and sports shoe. All volunteers were briefed about the risk and benefits involved with the experiment in the presence of their training instructors, and written informed consent was obtained before participation in the study. Soldier's fitness was checked by Army Medical Officer. According to the strict guidelines of Army Training Center, the minimum criterion for this special training course is: all volunteers must be in SHAPE-1 standard. It is a medical classification of a soldier, which determines the individual's fitness level. Those who fulfilled the criteria of SHAPE-1 standard were considered in this study.
Table 1: Physical characteristics (mean±standard error of mean) of volunteers (n=25)

Click here to view


Ethical approval

The study protocol conformed to the principles outlined by the Declaration of Helsinki protocol[18] and was also approved by the Institutional Ethical Committee (Ref no: IEC/DIPAS/D-1/2) on the use of human as study subjects.

Experimental details

The duration of training schedule was 12 weeks. At the end of 11 weeks of training, soldiers volunteered in this study. Volunteers were thoroughly explained about the purpose and significance of the study.

Participants reported to the training area in the morning at 5:00 a.m. Each participant was allotted a batch number before the start of the event. Baseline data were collected before commencing the experiment/training event. Training event was conducted in the presence of a training instructor from concerned training institute. The participants followed the standard training protocol of PPT, which is consisting of series of event such as 2.4 km run, 5 m shuttle run, and 100 m sprint and followed by other anaerobic events. All the training events were finished within the stipulated time as per the fulfillment criteria of training. Due to nature of secrecy, exact detail protocol cannot be provided. All the training events were conducted at 29°C–31°C temperature and 10%–20% relative humidity (RH).

Data collection and processing

The demographic data of all the participants were collected in front of training instructor in the training area before the start of the main experiment. All participants drank water ad libitum. The study was conducted during the morning hours between 05:00 and 06:00 a.m. The temperature and RH were recorded during training event using whirling psychrometer equipment (Dimple Thermometers, Delhi, India).

After finishing the event, each participant indicated his physical strain using the 15-point scale for rating of perceived exertion [Table 2]. The RPE scale value ranges from 6 to 20.
Table 2: Classification of physical strain using rating of perceived exertion score

Click here to view


Venous blood samples were drawn by a trained nursing assistant of the training institutions. Venous blood samples were drawn from each participant before and immediately after finishing the event. Approximately 5 mL blood from each subject was collected into ethylenediaminetetraacetic acid (EDTA)-coated tube. Then, EDTA tubes were centrifuged at 1000 g for 10 min. The separated plasma-containing tubes were placed in ice-cold condition and further stored at − 80°C until analyzed. Plasma samples were subsequently analyzed for Epi (CEA858Ge), NE (CEA907Ge), cortisol (Cayman-500360), serotonin (17-SEHRU-E01-FST), testosterone (CEA458Ge), aldosterone (CEA911Ge), and creatinine (DICT-500) using ELISA assay.

Statistical analysis

Data were passed the normality test followed by homogeneity of variance. Then, the Wilcoxon signed-rank sum test was performed for pre-post comparison. In the present study, the total numbers of participants were <30. The normality distribution of data was checked by Shapiro–Wilk test, and the homogeneity of variance of data was checked by Brown–Forsythe test. All the statistical analysis was conducted on GraphPad (Prism) version 5 (Prism version-5, GraphPad Software, California, USA). A level of significance was considered at P < 0.05.


  Results Top


The postexercise level of Epi (P < 0.001), NE (P < 0.01), cortisol (P < 0.001), serotonin (P < 0.01), aldosterone (P < 0.001), and creatinine (P < 0.05) was significantly increased, whereas the level of testosterone (P < 0.05) was significantly decreased as compared to its preexercise level [Figure 1].
Figure 1: Graphical representation of hormonal responses of pre- and postactivity (mean ± SEM). (a) Epinephrine; (b) Norepinephrine; (c) Cortisol; (d) Aldosterone; (e) Creatinine; (f) Testosterone; (g) Serotonin. SEM: Standard error of mean; Symbol: (*P ≤ 0.05); (**P ≤ 0.01); (***P ≤ 0.001)

Click here to view


The participants rated their perceived exertion as 15.20 ± 0.39 (mean ± standard error of mean) which provided the idea about the physical load experienced.


  Discussion Top


The present study was aimed to assess the hormonal responses of soldiers. Soldier's life is full of uncertain while the civilian personnel perform in very control and safe environment. The responses of military event are anomalous; such responses cannot be seen in any civilian events. Military trainings are composite of many activities. There are so many components meant to ensure and improve the flexibility and endurance of soldiers. The conjugated effect of all the components of training activity is demanding. The environmental thermal load is an additional burden to the combat training loads. All together are cumulative stressors that influence soldiers' performance. It is necessary to understand the hormonal responses of body adopting into such intense training event.

Cardiac and renal systems communicate bidirectionally and precisely to maintain hemodynamic stability and perfect perfusion in essential organs.[20] A previous study reported that the increased production and secretion of Epi and NE are required for cardiovascular and respiratory adjustments during intense exercise.[9],[10] Epi and NE bind to various G-protein-coupled receptors and subsequently activate the protein kinase A; further, it increases glycogenolysis and gluconeogenesis in skeletal muscle and liver, respectively, in order to fulfill the demand of energy required during exercise.[21],[22] Gomez-Merino et al. conducted a study on French Commando training program to assess the impact of training intensity on the Commandos, during which the Epi and NE increased by 1.2 and 2.3 folds as compared to their baseline level, respectively.[23] Similarly, Szivak et al.[24] have conducted a study on Survival, Evasion, Resistance, and Escape (SERE) training and found that the Epi and NE were increased by 1.7 and 2.9 folds, respectively. In the present study, the levels of Epi and NE were significantly increased by 1.8 and 1.9 folds, respectively, as compared to its preexercise level [Figure 1a and b]. Previous studies[23],[24] have observed the effect of entire training course on Epi and NE, whereas the present study was emphasized to quantify the impact of single bout of activity on Epi and NE level in circulation.

Cortisol is a catabolic hormone released in response to exercise by the adrenal cortex. Szivak et al. found that the cortisol was increased by 6.25 folds in soldiers during SERE training,[24] whereas in French commando, the cortisol level was increased by 1.06 folds as compared to pre-exercise level.[23] In the present study, the level of cortisol in plasma was also significantly increased by 1.45 folds as compared to its preexercise level [Figure 1c]. The cortisol level increases to cope up with the increased demand of energy during the exercise. In our study, the cortisol level was relatively lower as compared to SERE training and French commando training. The reason behind the difference between the responses of the present study and previously reported study would be the selection of type and training duration. A previous study revealed that difference in cortisol responses can be due to differences in the type of training and stimulus perceived.[25] It was assumed that more practicing physical exercises could be one of the causes behind decreasing cortisol in a chronic manner, and on the other hand, athletes present higher cortisol levels due to greater metabolic demands of sports practice.[26]

Cardiac and renal systems communicate bidirectionally and precisely to maintain hemodynamic stability and perfect perfusion in essential organs.[20] Aldosterone provides around 95% mineralocorticoid activity.[13] Kosunen et al.[27] have conducted a study on healthy runner and found that the aldosterone was increased by 1.23 times as compared to their basal level, whereas Patlar et al. (2019)[13] have conducted a study on ultra-marathon runner and found that aldosterone was increased by 6.08 times as compared to their basal level. In the present study, the plasma level of aldosterone was significantly increased by 1.88 folds as compared to its preexercise level [Figure 1d]. In addition to intense physical exercise, hot environment causes a significant loss of sodium and water.[13] This activity was done in the morning between 5:00 a.m. and 6:00 a.m., while the previously reported study was done for longer duration in relatively hot environment. The level of aldosterone is dependent on intensity and duration of exercise.[28] As the duration of exercise increased, the aldosterone may also increase in order to minimize the dehydration and mineral loss.[29]

The plasma level of creatinine is a commonly accepted measure of renal function.[30] The normal range of creatinine level in plasma is 0.7–1.3 mg/dL.[31] Banfi et al. (2006)[31] has conducted a study on basketball, racing, sailors, and soccer athletics and found that the basal level of creatinine was 1.3 mg/dL. In the present study, the creatinine level in plasma was 2.3 mg/dL and after exercise which was significantly high up to 3 mg/dL [Figure 1e]. It was found that the creatinine values are higher in elite athletics because of more release of creatinine from skeletal muscles. The increased concentration of creatinine may also be contributed by dehydration and reduction in renal blood flow.[14]

Testosterone level during military training can give understanding about the anabolic status of personnel.[24] Heavy physical demanding exercise can lower the resting concentrations of testosterone.[32] In the present study, the testosterone level was significantly decreased by 1.25 times as compared to their basal level [Figure 1f]. Gomez-Merino et al.[23] have conducted a 5-day military combat training; they have reported that the testosterone was significantly decreased by 1.54 times as compared to their baseline level. Friedl et al.[33] have conducted a study on US army ranger course, and they have reported that the testosterone level was significantly decreased by 4 times as compared to its preexercise level. Szivak et al.[24] have conducted a study on US soldiers during SERE training, and they have reported that the testosterone was significantly decreased by 2.7 times as compared to their basal level. The present study was conducted to observe the impact of single bout of intense activity on hormonal responses, whereas the previous studies were conducted to quantify the impact of entire training course. The basal level showed that soldiers were motivated before the exercise.[34] Soldiers in the present study would have felt exercise-induced anxiety as their basal level of testosterone revealed that they would regain their mental stability.

Fatigue is a complex phenomenon involving changes in the CNS.[35] According to the central fatigue hypothesis, increased concentration of serotonin in CNS during exercise increased exertion and fatigue.[16],[36] In the present study, the level of serotonin was significantly increased by 1.83 times as compared to its preexercise level [Figure 1g] and RPE score was 15.20 ± 0.39. Previous study conducted a study in a thermally controlled environment, during which serotonin was increased significantly by 3 folds as compared to its basal level, also the RPE score was observed to be 17; which indicating an overall decrease in the exercise capacity and an increased physical exertion of the participants.[36] The serotonin response was lower in the present study as compared to the finding reported by s previous study. Volunteers who participated in the present study might have more endurance power and capability to tolerate the stress imposed by the environment and intensity of the exercise. As the RPE score in the present study showed that the training activity was hard, which meant that in spite of hard activity, soldiers showed better resilience to counter in such extreme event and performed as per the set standards.


  Conclusion Top


The present study demonstrated that the physical proficiency training activity was highly energy demanding due to significantly increased sympathoadrenergic responses and induced a high level of acute stress due to significant reduction of testosterone. In addition to this, the significantly increased serotonergic responses indicated that the level of fatigue was high during activity. The findings of the present study may be helpful in screening of individuals before inducting into such intense military training activity to minimize the risk of injuries.

Limitation of this study

The present study was focused only on hormonal responses of the participants during intense military training activity.

Acknowledgments

The authors are thankful to the DRDO, Ministry of Defence and Ministry of Home Affairs, Government of India, for funding, infrastructure, and permission for this work. They are also thankful to the NSG Training Centre for providing logistics, technical support, and volunteers. They would like to express sincere gratitude to volunteers for their participation in the study. They are also acknowledging each and every individual who was indirectly involved in this work for their administrative and technical support. We are grateful for the cooperation and constant encouragement from Director, DIPAS, and other members of the Ergonomics Department.

Financial support and sponsorship

This study was financially supported by the Defence Research and Development Organization, Ministry of Defence, Government of India.

Conflicts of interest

There are no conflicts of interest.



 
  References Top

1.
Thomas JL, Adler AB, Wittels P, Enne R, Johannes B. Comparing elite soldiers' perceptions of psychological and physical demands during military training. Mil Med 2004;169:526-30.  Back to cited text no. 1
    
2.
Wilkinson DM, Rayson MP, Bilzon JL. A physical demands analysis of the 24-week British Army Parachute Regiment recruit training syllabus. Ergonomics 2008;51:649-62.  Back to cited text no. 2
    
3.
Bustamante-Sánchez Á, Tornero-Aguilera JF, Fernández-Elías VE, Hormeño-Holgado AJ, Dalamitros AA, Clemente-Suárez VJ. Effect of stress on autonomic and cardiovascular systems in military population: A systematic review. Cardiol Res Pract 2020;2020:1-9.  Back to cited text no. 3
    
4.
Blacker SD, Wilkinson DM, Bilzon JL, Rayson MP. Risk factors for training injuries among British Army recruits. Mil Med 2008;173:278-86.  Back to cited text no. 4
    
5.
Way of Ninja. The Modern Ninja's How to Guide to Training; 2020. Available from: https://www.wayofninja.com/. [Last accessed on 2020 Nov 10].  Back to cited text no. 5
    
6.
Holmes DS, Roth DL. Association of aerobic fitness with pulse rate and subjective responses to psychological stress. Psychophysiology 1985;22:525-9.  Back to cited text no. 6
    
7.
Brown JD, Siegel JM. Exercise as a buffer of life stress: A prospective study of adolescent health. Health Psychol 1988;7:341-53.  Back to cited text no. 7
    
8.
Silverman HG, Mazzeo RS. Hormonal responses to maximal and submaximal exercise in trained and untrained men of various ages. J Gerontol A Biol Sci Med Sci 1996;51:B30-7.  Back to cited text no. 8
    
9.
Leosco D, Parisi V, Femminella GD, Formisano R, Petraglia L, Allocca E, et al. Effects of exercise training on cardiovascular adrenergic system. Front Physiol 2013;4:1-7.  Back to cited text no. 9
    
10.
Howlett K, Galbo H, Lorentsen J, Bergeron R, Zimmerman-Belsing T, Bülow J, et al. Effect of adrenaline on glucose kinetics during exercise in adrenalectomised humans. J Physiol 1999;519:911-21.  Back to cited text no. 10
    
11.
Rojas Vega S, Strüder HK, Vera Wahrmann B, Schmidt A, Bloch W, Hollmann W. Acute BDNF and cortisol response to low intensity exercise and following ramp incremental exercise to exhaustion in humans. Brain Res 2006;1121:59-65.  Back to cited text no. 11
    
12.
Leers MP, Schepers R, Baumgarten R. Effects of a long-distance run on cardiac markers in healthy athletes. Clin Chem Lab Med 2006;44:999-1003.  Back to cited text no. 12
    
13.
Patlar S, Ünsal S. RAA system and exercise relationship. Turkish J Sport Exerc 2019;21:261-9.  Back to cited text no. 13
    
14.
Warburton DE, Welsh RC, Haykowsky MJ, Taylor DA, Humen DP. Biochemical changes as a result of prolonged strenuous exercise. Br J Sports Med 2002;36:301-3.  Back to cited text no. 14
    
15.
Kreuz LE, Rose RM, Jennings JR. Suppression of plasma testosterone levels and psychological stress. A longitudinal study of young men in Officer Candidate School. Arch Gen Psychiatry 1972;26:479-82.  Back to cited text no. 15
    
16.
Newsholme E, Acworth I, Blomstrand E. Amino-acids, brain neurotransmitters and a functional link between muscle and brain that is important in sustained exercise. In: Benzi G, editor. Advances in Myochemistry. London: John Libbey Eurotext Ltd.; 1987. p. 127-33.  Back to cited text no. 16
    
17.
Dyrstad SM, Giske R, Barlaug DG, Pensgaard AM. Relationship between soldiers' service performance and physical training volume. J Mil Vet Health 2010;18:7-11.  Back to cited text no. 17
    
18.
World Medical Association Declaration of Helsinki: Ethical Principles for Medical Research Involving Human Subjects; 2013. Available from: https://www.wma.net/policies post/ wma declaration-of-helsinki ethical principles for medical rese arch involving human subjects/. [Last accessed on 2020 Nov 10].  Back to cited text no. 18
    
19.
Borg GA. Psychophysical bases of perceived exertion. Med Sci Sports Exerc 1982;14:377-81.  Back to cited text no. 19
    
20.
Li LH, Kao WF, Chiu YH, Hou SK, Meng C, How CK. Impact of renin-angiotensin-aldosterone system activation and body weight change on N-terminal pro-B-type natriuretic peptide variation in 100-km ultramarathon runners. J Chin Med Assoc 2020;83:48-54.  Back to cited text no. 20
    
21.
Johanns M, Lai YC, Hsu MF, Jacobs R, Vertommen D, Van Sande J, et al. AMPK antagonizes hepatic glucagon stimulated cyclic AMP signalling via phosphorylation induced activation of cyclic nucleotide phosphodiesterase 4B. Nat Commun 2016; 7 (10856):1-12.   Back to cited text no. 21
    
22.
Xie W, Ye Y, Feng Y, Xu T, Huang S, Shen J, et al. Linderane Suppresses Hepatic Gluconeogenesis by Inhibiting the cAMP/PKA/CREB Pathway Through Indirect Activation of PDE 3 via ERK/STAT3. Front Pharmacol 2018;9:476.  Back to cited text no. 22
    
23.
Gomez-Merino D, Chennaoui M, Burnat P, Drogou C, Guezennec CY. Immune and hormonal changes following intense military training. Mil Med 2003;168:1034-8.  Back to cited text no. 23
    
24.
Szivak TK, Lee EC, Saenz C, Flanagan SD, Focht BC, Volek JS, et al. Adrenal stress and physical performance during military survival training. Aerosp Med Hum Perform 2018;89:99-107.  Back to cited text no. 24
    
25.
Papacosta E, Nassis GP. Saliva as a tool for monitoring steroid, peptide and immune markers in sport and exercise science. J Sci Med Sport 2011;14:424-34.  Back to cited text no. 25
    
26.
Moreira A, Freitas CG, Nakamura FY, Drago G, Drago M, Aoki MS. Effect of match importance on salivary cortisol and immunoglobulin A responses in elite young volleyball players. J Strength Cond Res 2013;27:202-7.  Back to cited text no. 26
    
27.
Kosunen K, Pakarinen A, Kuoppasalmi K, Näveri H, Rehunen S, Standerskjöld-Nordenstam CG, et al. Cardiovascular function and the renin-angiotensin-aldosterone system in long-distance runners during various training periods. Scand J Clin Lab Invest 1980;40:429-35.  Back to cited text no. 27
    
28.
Luger A, Deuster PA, Debolt JE, Loriaux DL, Chrousos GP. Acute exercise stimulates the renin-angiotensin-aldosterone axis: Adaptive changes in runners. Horm Res 1988;30:5-9.  Back to cited text no. 28
    
29.
Roy BD, Green HJ, Burnett M. Prolonged exercise following diuretic-induced hypohydration effects on fluid and electrolyte hormones. Horm Metab Res 2001;33:540-7.  Back to cited text no. 29
    
30.
Perrone RD, Madias NE, Levey AS. Serum creatinine as an index of renal function: New insights into old concepts. Clin Chem 1992;38:1933-53.  Back to cited text no. 30
    
31.
Banfi G, Del Fabbro M. Serum creatinine values in elite athletes competing in 8 different sports: Comparison with sedentary people. Clin Chem 2006;52:330-1.  Back to cited text no. 31
    
32.
Kraemer WJ, Fragala MS, Watson G, Volek JS, Rubin MR, French DN, et al. Hormonal responses to a 160-km race across frozen Alaska. Br J Sports Med 2008;42:116-20.  Back to cited text no. 32
    
33.
Friedl KE, Moore RJ, Hoyt RW, Marchitelli LJ, Martinez-Lopez LE, Askew EW. Endocrine markers of semistarvation in healthy lean men in a multistressor environment. J Appl Physiol 2000;88:1820-30.  Back to cited text no. 33
    
34.
Francis KT. The relationship between high and low trait psychological stress, serum testosterone, and serum cortisol. Experientia 1981;37:1296-7.  Back to cited text no. 34
    
35.
Cordeiro LM, Rabelo PC, Moraes MM, Teixeira-Coelho F, Coimbra CC, Wanner SP, et al. Physical exercise-induced fatigue: The role of serotonergic and dopaminergic systems. Braz J Med Biol Res 2017;50:e6432.  Back to cited text no. 35
    
36.
Zhao J, Lai L, Cheung SS, Cui S, An N, Feng W, et al. Hot environments decrease exercise capacity and elevate multiple neurotransmitters. Life Sci 2015;141:74-80.  Back to cited text no. 36
    


    Figures

  [Figure 1]
 
 
    Tables

  [Table 1], [Table 2]



 

Top
 
 
  Search
 
Similar in PUBMED
   Search Pubmed for
   Search in Google Scholar for
 Related articles
Access Statistics
Email Alert *
Add to My List *
* Registration required (free)

 
  In this article
Abstract
Materials and Me...
Results
Discussion
Conclusion
References
Article Figures
Article Tables

 Article Access Statistics
    Viewed260    
    Printed4    
    Emailed0    
    PDF Downloaded45    
    Comments [Add]    

Recommend this journal


[TAG2]
[TAG3]
[TAG4]