Rev Bras Fisiol Exerc 2022;21(3):195-203

doi: 10.33233/rbfex.v21i3.5160

REVIEW

Effects of confinement on the physical conditioning and health of submariners: a systematic review

Efeitos do confinamento sobre o condicionamento físico e saúde de militares submarinistas: uma revisão sistemática

 

Maria Elisa Koppke Miranda1,2, Priscila dos Santos Bunn1,2,3, Allan Inoue Rodrigues1,2, Rodrigo Gomes de Souza Vale2

 

1Marinha do Brasil, Centro de Educação Física Almirante Adalberto Nunes, Rio de Janeiro, RJ, Brazil

2Universidade do Estado do Rio de Janeiro (UERJ), Rio de Janeiro, RJ, Brazil

3Comando da Aeronáutica, Universidade da Força Aérea, Rio de Janeiro, RJ, Brazil

 

Received: April 27, 2022; Accepted: August 30, 2022.

Correspondence: Maria Elisa Koppke Miranda, Rua Aristides Lobo 115/603, bloco 1,

20250450 Rio de Janeiro, RJ  

 

Maria Elisa Koppke Miranda: maria_koppke@yahoo.com.br

Priscila dos Santos Bunn: priscilabunn@yahoo.com.br

Allan Inoue Rodrigues: allan_inoue@hotmail.com

Rodrigo Gomes de Souza Vale: rodrigogsvale@gmail.com

 

Abstract

Introduction: Submariners tend to be exposed to a metabolically unfavorable environment and occupational confinement factors that can affect their health, such as a sedentary lifestyle and high levels of stress. Objective: This systematic review aimed to analyze the effects of confinement on the physical conditioning and health of submariners. Methods: A literature search (January 2022) was performed using Pubmed, Cochrane, Web of Science, SPORTDiscus e Embase. The protocol was registered in the International prospective register of systematic reviews (CRD42021225362). Studies were included that sampled submariners on mission, whose outcome was indicators of health or physical performance. Results: From a total of 2,334 articles, 5 studies were included in the review. The following were analyzed: cardiorespiratory fitness, body composition; the food frequency; the frequency of physical activity; the lipid profile, bone function markers and specific neuromotor tests; both in the comparison of onboard and non-embarked military personnel, as well as for only embarked personnel, or military personnel who worked on small or large submarines compared to military personnel who worked on aircraft carriers. Submariners show a negative change in the analysis of body composition, aerobic performance, biochemical analysis of lipids, bone function markers and endocrine regulators. Conclusion: Prolonged time aboard a submarine can compromise the health of the military.

Keywords: military personnel, submariner, physical training.

 

Resumo

Introdução: Os submarinistas tendem a ser expostos a um ambiente metabolicamente desfavorável e fatores ocupacionais de confinamento que podem afetar sua saúde, como o estilo de vida sedentário e altos níveis de estresse. Objetivo: Esta revisão sistemática teve como objetivo analisar os efeitos do confinamento sobre o condicionamento físico e saúde de militares submarinistas. Métodos: Uma pesquisa bibliográfica (janeiro de 2022) foi realizada usando Pubmed, Cochrane, Web of Science, SPORTDiscus e Embase. O protocolo foi registrado no Registro Internacional Prospectivo de Revisões Sistemáticas (CRD42021225362). Foram incluídos estudos que tinham como amostra submarinistas em missão, cujo desfecho era indicadores de saúde ou de desempenho físico. Resultados: De um total de 2.334 artigos, 5 estudos foram incluídos na revisão. Foram analisadas: a aptidão cardiorrespiratória, a composição corporal; a frequência alimentar; a frequência de atividade física; o perfil lipídico, os marcadores de função óssea e testes neuro motores específicos; tanto na comparação de militares embarcados com não embarcados; quanto para somente embarcados, ou militares que trabalhavam em submarinos de pequeno ou grande porte comparados com militares que trabalhavam em porta-aviões. Militares submarinistas apresentam alteração negativa na análise da composição corporal, desempenho aeróbio, análise bioquímica de lipídeos, marcadores de função óssea e reguladores endócrinos. Conclusão: O tempo prolongado a bordo de um submarino pode comprometer a saúde dos militares.

Palavras-chave: militares; submarinista; treinamento físico.

 

Introduction

 

The population of submariners is epidemiologically unique, whose initial health status is considered good, as they undergo a specialized selection process and specific professional training [1]. However, submariners tend to be exposed to a metabolically unfavorable environment and occupational confinement factors that can affect health, such as a sedentary lifestyle [2], sleep deprivation [3], shift work [3,4], and high levels of stress [4].

Underwater activities involve prolonged periods of submersion with limited opportunity for physical exercise and a compromised supply of fresh food. The environmental conditions inside the vessel can contribute to cardiometabolic health problems, mainly impacted by the decrease in the practice of physical activity [2,5]. Long periods at sea can reduce aerobic conditioning in submariners [6]. It can impair the performance related to the specific underwater task, especially concerning restricted oxygen consumption during missions [7]. In addition, there is a change in the Body Mass Index (BMI) [6], indicating an increase in body fat levels after a mission [8], which can compromise the health of the military, as well as work in a restricted workspace.

Bennett, Schlichting & Bondi [9] reviewed previous research that tried to measure physical deconditioning in submariners. A progressive increase in heart rate was observed after exercise, as a sign of cardiovascular compensation to maintain cardiac output. Knight et al. [10] reported a decrease of approximately 13% in maximal oxygen consumption (VO2max) measured by pre-and post-shipment levels. This implies that the health of these individuals may be compromised by the potential sedentary lifestyle. On the other hand, in adult men, a 1 MET increase in VO2max was associated with a 12% decrease in risk for all-cause mortality and cardiovascular diseases [11]. In this sense, the higher the VO2max, the better the individual's health status.

In this way, submariners need to adapt to working conditions and perform regular physical exercises in a confined environment. However, little is known about the physical conditioning and health of submariners [12]. Therefore, the objective of the present systematic review was to analyze the effects of confinement on the physical conditioning and health of submariners.

 

Methods

 

The present systematic review was written following the guidelines of the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) [13]. The study protocol was registered in the International Prospective Registry of Systematic Reviews (CRD42021225362).

 

 Search strategy

 

A search was performed in January 2022, in Pubmed, Cochrane, Web of Science, SPORTDiscus, and Embase databases. The following descriptors were used: "submariner" and “physical training” or “physical conditioning”, or “exercise tests”, together with their synonyms. The search phrases were obtained using the Boolean operators AND (between descriptors) and OR (between synonyms). In addition, the reference lists were explored to find additional relevant studies. There was no period and language delimitation for the search.

 

Eligibility criteria

 

The studies included in the review met the criteria described in Table I.

 

Table I - Inclusion criteria

 

 

Selection of studies and data extraction

 

Eligibility assessments of studies were performed independently by two reviewers. Studies were downloaded to Mendeley Desktop (version 1.19.8) and duplicates were removed before being sorted by title and abstract. The full texts of the remaining studies were retrieved and assessed for eligibility. Any disagreements regarding the inclusion of a particular study were resolved through a consensus meeting or decided by a third reviewer.

The following data were extracted from the included studies: author, year of publication, participant characteristics, sample size, study design, exposure, control, evaluation, follow-up, and results. Data extraction from selected studies was independently processed by two reviewers and disagreements were resolved through a consensus meeting or a decision by a third reviewer.

 

Assessment of the methodological quality of the studies

 

The National Institutes of Health (NIH) Quality Assessment Tool for observational cohort and cross-sectional studies (https://www.nhlbi.nih.gov/health-topics/study-quality-assessment-tools) was used to assess the risk of bias in included studies. Reviewers answered each question as “Yes”, “No”, “Unable to determine”, “Not applicable” or “Not reported”, based on the critical review of each study. Questions answered with “'Yes” received a score of 1, while questions answered with “No”, “Unable to determine”, or “Not reported” received a score of 0. The total score from each study was used to classify the risk of bias as low (10-14), moderate (5-9), or high (0-4). The methodological quality assessment was performed by two experienced evaluators independently. Any disagreements were resolved through a consensus meeting or a decision by a third evaluator.

 

Results

 

Selection of studies

 

A total of 2,334 articles were identified and 121 duplicate titles were removed. After screening citations, 2,193 did not meet the inclusion criteria and were excluded. A summary of search results and reasons for exclusion are shown in Figure 1. Five studies were included in this systematic review and are summarized in Table II.

 

 

Figure 1 - Flow diagram of the studies included in this systematic review about the effects of confinement on the physical conditioning and health of submariners

 

Table II - Characteristics of the studies included in the systematic review

 

 

Methodological quality of studies

 

The scores of the studies included in the present systematic review ranged from 7 (moderate risk of bias) to 5 (high risk of bias) out of 14 possible points (Table III). Three studies were classified as having a moderate risk of bias [5,7,14], while two studies were classified as having a high risk of bias [1,6]. All studies in this review included the research question or objective (item 1), clearly specified the study population (item 2), and all subjects were selected or recruited from the same or similar populations (item 4). All studies presented valid and reliable outcome measures (item 11). However, most studies did not justify the sample sizes (item 5) and did not show a control [measurement and adjustment] over confounding variables (item 14).

 

Table III - Quality assessment tool for observational cohort and cross-sectional studies

 

 

Discussion

 

The main results of this systematic review were: that military submariners showed a negative change in the analysis of body composition, aerobic performance, biochemical analysis of lipids, bone function markers, and endocrine regulators. In addition, the studies investigated factors such as food frequency; the frequency of physical activity; and specific neuromotor tests. There was a comparison of onboard and non-embarked military personnel, as well as the results only for embarked personnel, or military personnel who worked on small or large submarines compared to military personnel who worked on aircraft carriers.

The analysis of body composition was considered in most of the studies included. Fifty-three soldiers decreased their total body mass (5%) and fat mass (11%) after a three-month mission in an American nuclear submarine [5]. The authors justify this fact with the decrease in caloric intake. On the other hand, an increase in BMI was observed after a three-month mission of 52 military personnel in a non-nuclear American submarine [14]. In a cross-sectional study [6], the authors reported a higher BMI for submariners when compared to aircraft carrier military, corroborating the Korean study comparing submariners with non-submariners [1]. It is important to point out that high BMI is associated with many health problems such as diabetes and heart disease, and has been observed as a risk factor for musculoskeletal injuries, such as low back pain and lower limb injuries [15], in addition to being a labor complicating factor for environments with restricted spaces such as the interior of a submarine [16].

During a submarine mission, physical activity is severely reduced for most individuals because of the strictly reduced space and working hours [17]. Among the effects resulting from physical deconditioning can be mentioned the rapid decrease in VO2max [15]. Fothergill and Sims [7] applied the Cooper test before and after a 33-day mission and in a non-detached control group, they found a decrease in the distance covered, indicating a decrease in cardiorespiratory fitness, corroborating the results of the study by Gregg et al. [6], only for the 2000m test. The same study analyzed the heart rate (HR) variation during the test in both groups. The decrease in the performance of the standouts was not associated with any changes in mean HR and maximum HR, however, the HR recovery time was longer. In addition, recovery HR decreased for those highlighted after exposure.

A study brought a neuromotor assessment of the military, using the Navy Fitness Readiness Test as a way to assess the physical readiness of submariners [6]. As a result, the score in the physical test of small submarine soldiers was lower than that of aircraft carrier soldiers, indicating worse results for the abdominal and arm flexion tests.

Regarding the lipid profile and other blood markers, in biochemical analysis, after three months of mission in a nuclear submarine [5], modest improvements in serum lipids were observed, as well as an average reduction in protein 10 induced by interferon-gamma, in the protein 1 and monocyte chemotactic. This fact can also be explained by the fact that energy intake is reduced. A study that analyzed the Metabolic Syndrome in this population [1] showed lower High-Density Lipoprotein (HDL) Cholesterol and increased Fasting Glucose, compared to non-submariners.

Prolonged submersion led to a significant decrease in bone strength, accompanied by a decrease in bone metabolism, in a study after a 30-day mission aboard a non-nuclear submarine [14]. There was an increase in the levels of albumin and circulating calcium. Parathyroid hormone and 25-hydroxyvitamin D levels decreased significantly. Significant decreases were also observed in the levels of Acid Phosphatase 5 and C-terminal Telopeptide Fragment, markers of bone resorption, as well as in type I collagen N-terminal Propeptide.

The present study carried out an extensive search in the main databases related to health and related areas, using a large number of descriptors and synonyms in the search equations. However, the study is not free from limitations. Among them, we can highlight the lack of articles dealing with specific physical training for this submariner population. In addition, there were a small number of studies eligible for the review that had a moderate or low risk of bias.

 

Conclusion

 

Military submariners present changes in the analysis of body composition, biochemical analysis of lipids, bone function markers, and endocrine regulators. In addition, prolonged time aboard a submarine can compromise aerobic performance, which can affect the health of the military. It is suggested to carry out new studies, with a controlled and randomized design, with better methodological quality, especially taking precautions related to the control of confounding variables and justification for the sample sizes.

 

Conflicts of interest

There are no conflicts of interest.

 

Financing source

There is no funding.

 

Authors' contribution

Research conception and design: Miranda MEK, Bunn PS, Rodrigues AI, Vale RGS; Data collection: Miranda MEK, Bunn PS, Rodrigues AI; Data analysis and interpretation: Miranda MEK, Bunn PS, Rodrigues AI; Manuscript writing: Miranda MEK, Bunn PS, Rodrigues AI, Vale RGS; Critical review of the manuscript for important intellectual content: Miranda MEK, Bunn PS, Rodrigues AI, and Vale RGS

 

References

 

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