Occupational Medicine Advance Access published online on January 11, 2007
Occupational Medicine, doi:10.1093/occmed/kql170
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Short Report |
Smoking and injury in Royal Marines' training
Institute of Naval Medicine, Alverstoke, Gosport, Hampshire, UK
Correspondence to: Kathy Munnoch, Institute of Naval Medicine, Crescent Road, Alverstoke, Gosport, Hampshire PO12 2DL, UK. Tel: +44 2392 768 056; fax: +44 2392 504 823; e-mail: hsohf2{at}inm.mod.uk
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Abstract |
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Background Training for the Royal Marines (RMs) is considered to be one of the most arduous military training regimes in the world. Approximately 16% of the annual intake of recruits suffer an injury. Smoking has been found to be a predisposition to injury.
Objective To examine the relationship between recruits' smoking status on entry to training and subsequent incidence of injury.
Method Retrospective, longitudinal analysis of 1 year's intake of RM recruits at Commando Training Centre Royal Marines.
Results A significantly greater proportion of RM recruits who were smokers on entry to training experienced a physical injury during the course than their non-smoking counterparts (chi-square = 8.15, P < 0.01). A recruit who smoked on entry to training was almost twice as likely to acquire an injury during training [relative risk = 1.7 (95% CI = 1.2–2.8)].
Conclusion Smoking status of RM recruits in training was significantly associated with injury.
Keywords Armed forces; health psychology; injury; rehabilitation; smoking
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Introduction |
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Previous research has identified a number of factors associated with injury in military populations, including smoking. Jones et al. [1] found that cigarette smoking in US army trainees was related to traumatic injury (e.g. fractures and ankle sprains) with a relative risk of 1.7. Likewise, Knapik et al. [2] found smoking 20 cigarettes a day to have a relative risk of 2.8 for subsequent injury during army basic combat training. The Royal Marines' (RMs) 32-week training course is considered to be one of the most arduous military training regimes in the world. Approximately 16% of the annual intake of recruits suffer an injury and is ‘backtrooped’ to ‘Hunter Company’ for rehabilitation. Given that the average recovery time in Hunter Company is 14 weeks (almost half of the length of the entire training course), it is imperative that the Commando Training Centre Royal Marines (CTCRM) identifies predictors of injury and implements interventions to reduce its incidence. The aim of this study was to analyse data already available on a cohort of recruits, to investigate whether any of the variables were associated with injury. This paper confines itself to the role of smoking and injury.
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Methods |
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Ethical approval was obtained from the MoD Navy Personnel Ethics Research Committee and Data Protection Act 1998 requirements were met. All recruits from the training year 2001 to 2002 were informed of the study by post and given the opportunity to decline the inclusion of their data. The RM is an all-male elite fighting force; therefore, there were no females in the sample. Smoking status on entry to RM training and injury data were collected from a medical database held at CTCRM. NB. A recruit was classed as a non-smoker, if he reported on entry to training that he did not smoke cigarettes. Recruits were classed as smokers when they reported on entry to training that they smoked, and were categorized according to their daily cigarette consumption. Injury data included categorical information on specific injuries (e.g. numbers of stress fractures, etc.). While no data were available alluding to socio-economic status, educational test scores indicative of socio-economic status were available. These included English test scores, mathematics test scores, mechanical comprehension test scores and verbal reasoning test scores, as well as age. Physical fitness data were collected at the time of recruitment, including bleep test level, assault course time, height, weight and body mass index. These variables were analysed as possible confounders/covariates to smoking and injury. Alcohol consumption data were not collected. Using chi-square and Mann–Whitney U-tests, the data were analysed for differences between Hunter Company recruits and recruits who had completed mainstream training without suffering an injury sufficiently severe to warrant transfer to Hunter Company.
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Results |
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A total of 1115 male RM recruits were included in the study out of 1 year's intake of 1132 who could have been included in the study (mean age = 20, SD = 3). Table 1 summarizes the number of smokers and non-smokers in the sample by injury.
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One hundred and fifty recruits (13%) were smokers and 36 of these suffered an injury (24%). Of the non-smoking recruits, 15% suffered an injury (chi-square = 8.15, df = 1, P < 0.05).
Table 2 shows the numbers of injured smokers and non-smokers by type of injury.
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Even though 30% of the sample was suffering from stress fractures, categorical analysis revealed that there were no significant differences with respect to type of injury (fractures and stress fractures) and smoking habit. Analyses were carried out using smoking as a categorical outcome based on number of cigarettes smoked per day, as well as dichotomous (smoker/non-smoker). No significant relationships were found between educational test scores collected and smoking status or injury, respectively (Table 3). Smokers were not significantly older, less fit or overweight than their non-smoking counterparts. A significant difference (chi-square = 8.15, P < 0.01) was found between the smoking status of recruits who became injured and those who did not (24% of smokers became injured compared with 15% of non-smokers). Table 3 illustrates that (other than smoking) only age was significantly related to injury. Further analysis revealed that age and smoking status were not related (Mann–Whitney U-test = 444.500, P = 0.18: a non-parametric test was used because the distributions of the variables in Table 3 were not normal).
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Logistic regression revealed that age accounted for 2.4% and smoking accounted for 4% of the variance in injury (R2 = 0.024 and 0.04, respectively).
The relative risk of injury for recruits who smoked was 1.7 (95% CI = 1.2–2.8). The proportion of recruits in rehabilitation who smoked >10 cigarettes a day was almost twice that of uninjured recruits not in mainstream training with a similar habit. Smoking 1–9 cigarettes a day resulted in a relative risk of 1.2 (95% CI = 0.6–2.6). Smoking >10 cigarettes a day, however, resulted in a relative risk of injury of 1.9 (95% CI = 1.3–2.8).
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Discussion |
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Our study found that smokers undertaking training for the RMs were more likely to be injured than non-smokers. Those who smoked 10–19 cigarettes a day had a relative risk of injury of 1.9 (95% CI = 1.2–2.8). There are several possible explanations as to why smoking should be related to injury. Firstly, physical fitness and injury are inversely related and this relationship is potentiated by smoking [1]. Secondly, it has been suggested that smoking affects bone strength, although the present findings do not indicate that smoking is associated with fracture or stress fracture, in particular [3,4]. Finally, there is evidence that smoking is indicative of risk taking behaviour and that those who smoke are more likely to also take physical risks during training that may result in an injury [2].
We did have data available on possible confounders, including English test scores, mathematics test scores, mechanical comprehension test scores and verbal reasoning test scores, but none of them were related to smoking or to injury. Only age significantly differentiated between the injured and non-injured samples. It is possible that smoking is associated with socio-economic status. However, there is a paucity of literature relating socio-economic status to physical injury, whereas the mechanisms behind smoking and injury are better documented. Smoking status and age were not related.
The association between smoking and injury is remarkable in such a young and otherwise healthy population. Recruits are usually very fit on joining the RMs, partly not only because the stringent physical and medical selection tests exclude unfit individuals but also because most recruits are already keen sportsmen. The length of time to rehabilitate injured recruits was indicative of the severity of these injuries.
A possible intervention would be to reinforce the message, prior to and throughout training, that smokers are more prone to injury. Promulgation of information detailing the negative effects of smoking to recruits prior to them joining training, as well as advertisement of the smoking cessation clinics provided by the RMs could help to reduce the number of smokers and potentially reduce the likelihood of injury. The continuous monitoring of recruits' smoking behaviour would facilitate further study in this area. This could be carried out in conjunction with a study to ascertain what happens to injured smokers after rehabilitation, in terms of whether they become reinjured, how they perform during their remaining time in training and how they fare in-service.
Key points
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Conflicts of interest |
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None declared.
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Acknowledgements |
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Thanks to the staff of CTCRM for assisting with the project. This project was supported by the Ministry of Defence, Royal Navy.
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References |
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- Jones BH, Bovee MW, Harris III, et al. (1993) Intrinsic risk factors for exercise-related injuries among male and female army trainees. Am J Sports Med 21:705–710.
[Abstract/Free Full Text] - Knapik JJ, Sharp MA, Canham-Chervak M, et al. (2001) Risk factors for training-related injuries among men and women in basic combat training. Med Sci Sports Exerc 33:946–954.
- Rhee EJ, Oh KW, Lee WY, et al. (2004) Age, body mass index, current smoking history, and serum insulin-like growth factor-I levels associated with bone mineral density in middle-aged Korean men. J Bone Miner Metab 22:392–398.[Web of Science][Medline]
- Kanis JA, Johnell O, Oden A, et al. (2005) Smoking and fracture risk: a meta-analysis. Osteoporos Int 16:155–162.[CrossRef][Web of Science][Medline]
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