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 Table of Contents  
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
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/bjhs.bjhs_14_21

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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)

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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

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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)

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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.


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

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  [Figure 1]

  [Table 1], [Table 2]


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