Body Mass Index, Physical Activity, and Smoking in Relation to Military Readiness

Transcription

1 MILITARY MEDICINE, 179, 8:901, 2014 Body Mass Index, Physical Activity, and Smoking in Relation to Military Readiness Cdt Audrey Colle e* ; Peter Clarys, PhD ; Lt Col Philippe Geeraerts*; Cdt Christian Dugauquier*; Patrick Mullie, PhD* ABSTRACT The objective of the study was to analyze the influence of excess weight, regular physical activity, and smoking on the military readiness of the Belgian Armed Forces in a cross-sectional online survey. A multinomial logistic regression was used to study the influence of modifiable risk factors on participation in the physical fitness test. In our study population (n = 4,959), subjects with a body mass index higher than 25 kg/m 2, smokers, and subjects with a lower level of vigorous physical activity were significantly more likely to have failed the physical fitness test. In the Belgian Armed Forces, serious efforts should be made to encourage vigorous physical activity, smoking cessation, and weight loss to preserve our military readiness. Instead of relying on civilian public health interventions, Belgian Defense should develop its own specific approaches to prevent weight gain, improve physical fitness, and influence smoking attitude. INTRODUCTION The role of the armed forces of European countries has changed since the Cold War. 1 A complex and unpredictable security environment has replaced the threat of large-scale interstate war. The structure of the armed forces has evolved from mass forces based on conscription to smaller, professional, volunteer forces. The fact that this smaller military force has to operate within the confines of economic austerity but yet faces increasingly frequent deployment in multinational operations has heightened the need to maintain a high state of readiness to guarantee projection capacities. Military physical fitness test (PFT) failure has the potential to negatively influence the operational readiness of the forces. In the Belgian Armed Forces, military personnel who fail the PFT are not eligible for deployment, and in cases of candidacy, failure can even lead to dismissal. Several studies in the general population have highlighted the negative influence of excess weight, smoking, and physical inactivity on physical condition. 2 4 In the military population, we would expect a lower prevalence of weight issues, smoking, or physical inactivity than in the general population because of the physical and medical selection criteria used at recruitment and the physically demanding conditions of the military role. However, prevalence studies have shown that weight problems are also present in several armed forces including the U.K. Armed Forces, 5 the U.S. Armed Forces, 6 the Royal Netherlands Army, 7 the Australian Defense Forces, 8 the German Bundeswehr, 9 the Finnish Armed Forces, 10 and the French Armed Forces. 11 The situation is no different in the Belgian Armed Forces. 12 Against our expectation, the rate of current smokers among active duty service members within the U.S. Armed Forces *Unit of Epidemiology and Biostatistics, Staff Department Well Being, Belgian Defence, Bruynstreet 1, B-1120 Brussels, Belgium. Faculty of Physical Education and Physiotherapy, Department of Human Biometry and Biomechanics, Vrije Universiteit Brussel, Pleinstraat 2, B-1050 Brussels, Belgium. doi: /MILMED-D was higher for younger service members compared to their civilian counterparts and similar for older members compared to the rate among the civilian population. 13 As expected, active duty military personnel reported higher rates of physical activity compared to the civilian population. 13,14 Few studies 15,16 have examined the relationships between excess weight, smoking, and physical fitness in an active duty military population. Macera et al 15 examined self-reported smoking status and change in objectively measured fitness over 1 to 4 years while controlling for body mass index (BMI) in a large sample of male U.S. Navy personnel. They found that higher BMI and smoking were associated with slower 1.5 miles run/walk times, poorer upper and core fitness, after adjustment for age and rank. Zajdowicz et al 16 investigated potential predictors of physical readiness test results and found that being obese or overweight was associated with physical readiness test failure after adjustment for sex, race, rank, and age. Crawford et al 17 compared PFT results between soldiers with a body fat (BF) > 18% and those with a BF 18% and found that only push-ups were significantly different between the two groups. To the best of our knowledge, no studies have been published on the association between excess weight, smoking, and PFT results while controlling for physical activity in an active duty military population. As military personnel are physically active, it is important to include physical activity in the multivariate analysis. In this study, we evaluated the combined relationships between BMI, smoking, level of physical activity, and PFT results in the Belgian Armed Forces. Our study attempted to quantify this relationship in a military occupational setting: how much do excess weight, smoking, and level of physical activity are related to the PFT results? METHODS In January 2013, a total of 26,566 military personnel with address, representing 84.6% of the 31,412 men and women in active service, were invited to MILITARY MEDICINE, Vol. 179, August

2 participate in an online survey with questions concerning BMI, smoking habits, and physical activity levels. The invitations presented the option to complete the survey using either an Internet or intranet questionnaire. Answers to the questionnaire were completely anonymous and the time limit to complete the questionnaire was 2 weeks. The outcome variable was PFT results. In the Belgian Armed Forces, all military personnel under the age of 50 are required to perform a PFT at least once a year. Participants are scored based on their performance in three tests consisting of push-ups, sit-ups, and a 2,400-m run. Scores range between 0 and 100 points for each exercise. A minimum score of 50 for each exercise is required to pass the test. A participant s overall score is the sum of the points from the three exercises. Self-reported PFT results in 2012 were based on responses to the question In the last year, did you pass your physical fitness test? Yes, No, or Did not participate response choices were provided. BMI was calculated by dividing self-reported weight (in kilograms) by self-reported height squared (in meters) and was used to define subjects as healthy (<25 kg/m 2 ), overweight ( kg/m 2 ), and obese (>29.9 kg/m 2 ). For smoking status, subjects were classified as current, former, or never smokers. The International Physical Activity Questionnaire (IPAQ) short form 18 was used to report frequency and duration of walking, as well as moderately and vigorously intensive activities performed for at least 10 minutes duration per session. IPAQ also collected information on total sitting time. Weekly minutes of walking and participation in moderately intensive and vigorous activities were calculated separately by multiplying the number of days per week by the duration on an average day. Reported minutes per week in each category were weighted by a metabolic equivalent (MET; multiples of resting energy expenditure) resulting in a physical activity estimate independent of body weight, expressed in MET-minutes per week and computed by multiplying METs by minutes per week. All physical activity variables in MET-minutes per week (walking, vigorous and moderate physical activity) were categorized into tertiles so that the relative difference in the outcome variable between the least and the most physically active groups could be observed. Demographic and military data were obtained from the questionnaire, including birth year, marital status (married/ cohabitation versus divorced/separated/widow or single), rank (officer, noncommissioned officer, or enlisted soldier), and percentage of daily administrative tasks. Statistical analysis was restricted to men under the age of 50 because of the small percentage of women and because only military personnel under 50 are required to perform a PFT. All descriptive data were presented as percentages, or as median and interquartile range when appropriate. Characteristics of the participants among PFT results were compared using c 2 and Kruskal Wallis tests. Multinomial logistic regression was used to study the association between BMI, smoking, physical activity, and PFT results (pass versus fail or did not participate). Smoking (never, former, current), walking, vigorous and moderate physical activity (low, medium, high), BMI (healthy, overweight, obese), and age (continuous) were forced into all models, and backward elimination (p 0.05) was used to obtain a final multivariate model. The following variables were evaluated as possible confounders in multivariate models: military rank (officer, noncommissioned officer, and enlisted soldier), marital status (single or married), and percentage of daily administrative tasks. Interactions of BMI and physical activity (vigorous, moderate, and walking) were tested. Results of the multinomial logistic regression were presented as odds ratios (ORs) with 95% confidence intervals. Tests for trends across categories of variables present in the model were executed by assigning equally spaced values (e.g., 1, 2, 3, or 4) to the categories and treating the variables as continuous variables in the multinomial logistic regression analysis. All p values were two-sided, and a 5% level of statistical significance was used. The data were analyzed by using IBM SPSS statistics for Windows Version 19.0 (IBM Corp, Armonk, New York). This study was conducted according to the guidelines laid down in the Declaration of Helsinki, and all procedures involving the participants were approved by the Bioethical Committee of the University of Brussels (Vrije Universiteit Brussel). RESULTS Out of 6,558 participants in the study, 4,959 military men under 50 responded to the survey. The distribution of the participants within the three PFT categories was as follows: 70% passed the PFT, 9.6% failed the PFT, and 18% did not participate. Table I shows characteristics of the study population according to categories of participation in PFT. 75 % of them were older than 38 years and the median age was 44 years. The majority of the participants belonged to the category of officers or noncommissioned officers (79%), and was married or in cohabitation (76%). Six out of 10 participants were obese or overweight (61%), and one out of two participants was never smoker (59%). The median for walking, moderate and vigorous physical activity was respectively 346.5, 300, and 960 MET-min/wk. Participants who declared having passed the PFT were more likely to be officers and nonsmokers, to have a healthy weight and to participate in both vigorous and moderate physical activities. Results from the multinomial logistic regression are presented in Table II. The multivariate model (multivariable OR) included age as a continuous variable, rank (officer, noncommissioner officer, enlisted soldier), BMI (healthy weight, overweight, obese), smoking status (current, former, never), vigorous physical activity (low, medium, high), moderate physical activity (low, medium, high), and walking (low, medium, high). In multinomial logistic regression adjusting for age, rank, and physical activity, subjects who failed or 902 MILITARY MEDICINE, Vol. 179, August 2014

3 TABLE I. Characteristics of the Study Participants by Categories of PFT Outcome Total PFT n (%) No. % Pass Fail Did Not Participate p Value* Median Age in Years (IQR) 44 (9) 43 (11) 45 (6) 46 (5) <0.001 Military Rank Officers 1, (85) 58 (6) 97 (9) Noncommissioned Officers 2, ,849 (69) 315 (12) 515 (19) Enlisted Soldiers (59) 102 (11) 281 (30) <0.001 Marital Status Single 1, (69) 122 (11) 221 (20) Married 3, ,481 (71) 353 (10) 672 (19) NS Smoking Status Never 2, ,769 (77) 193 (8) 351 (15) Former 1, (67) 140 (12) 261 (22) Current 1, (61) 142 (13) 281 (26) <0.001 BMI (kg/m 2 ) Healthy Weight (<25.0) 1, ,533 (84) 75 (4) 212 (12) Overweight ( ) 2, ,510 (69) 240 (11) 439 (20) Obese (³30) (32) 160 (27) 242 (41) <0.001 Vigorous Physical Activity (MET-Minutes/Week) Low 1, (51) 215 (16) 457 (33) Medium 1, ,242 (77) 157 (10) 212 (13) High 1, ,292 (80) 103 (6) 224 (14) <0.001 Moderate Physical Activity (MET-Minutes/Week) Low 1, (65) 173 (13) 294 (22) Medium 1, ,154 (68) 172 (10) 364 (22) High 1, ,196 (77) 130 (8) 235 (15) <0.001 Walking (MET-Minutes/Week) Low 1, (72) 150 (11) 235 (17) Medium 1, ,105 (71) 165 (11) 290 (18) High 1, ,152 (69) 160 (9) 368 (22) <0.05 IQR, interquartile range. *p value (two sided) for c 2 test (categorical variables) or Kruskal Wallis test (continuous variable). who did not participate in the PFT were more likely to be obese or overweight or to smoke than subjects who passed the PFT (Table II). After adjustment for age, rank, smoking, and BMI, subjects in the moderate-to-high tertile of vigorous physical activity had a 50% to 72% lower odds of failing the PFT and a 65% to 75% lower odds of not taking the PFT compared with the lowest tertile (p for trend < 0.001). After adjustment for age, rank, BMI, smoking, moderate physical activity, and vigorous physical activity, no statistical-significant association was noted between walking and performance in the PFT except for subjects with a high level of walking who had an increased odds of not participating in the PFT versus passing the PFT. After adjustment for age, rank, BMI, smoking, walking, and vigorous physical activity, moderate physical activity was not significantly associated with failing the PFT versus passing the PFT or with not participating in the PFT versus passing the PFT. After multivariate adjustment, no interaction of BMI and physical activity was statistically significant. Finally, subjects who failed the PFT were more likely to be overweight or obese, to smoke, and to participate in fewer vigorous physical activities compared with subjects who passed the PFT. Subjects who did not participate in the PFT were more likely to be overweight or obese, to smoke, and were also less likely to perform vigorous physical activities. Adjustment for potential confounding factors did not alter these associations. DISCUSSION Our findings suggest that subjects who were both overweight and who smoked had an increased risk of failure or nonparticipation in the PFT. In this cross-sectional study, subjects who performed vigorous physical activity had a significantly reduced risk of failure or nonparticipation in the PFT. Against expectation, subjects who walked frequently had an increased risk of nonparticipation in the PFT. A possible explanation could include medical conditions such as back or knee pain forcing the subjects into walking instead of doing other sports. These conditions could then explain the higher rate of nonparticipation in the PFT. Another possible explanation could be that military strenuous marching was reported as walking in the questionnaire and military training activities, such as marching, are known risk factors of injuries, resulting in days of limited duty. 19 Some limitations of this study must be taken into account. Only 21% of participants were enlisted soldiers, which is far below the 42% of enlisted soldiers in the Belgian Armed Forces as a whole. Rank is an indicator of the socioeconomic status of a participant and is inversely associated with MILITARY MEDICINE, Vol. 179, August

4 TABLE II. Multinomial Logistic Regression With Results for PFT as Categorical Dependent Variable: Effects of BMI, Physical Activity, and Smoking (n = 4,959) Fail Versus Pass Did Not Participate Versus Pass Age-Adjusted OR a Multivariable OR a,b 95% CI Age-Adjusted OR a Multivariable OR a,b 95% CI BMI (kg/m 2 ) Healthy Weight (<25.0) Referent Referent Overweight ( ) Obese (³30) Smoking Status Never Referent Referent Former Current Vigorous Physical Activity Medium High Moderate Physical Activity Medium High p for Trend NS NS Walking Medium High p for Trend NS <0.001 CI, confidence interval. a OR from multinomial logistic regression. b Adjusted for age, rank, and mutually adjusted for all variables listed in the table. physical fitness. 15 The study participants were also more likely to be slightly older than the average Belgian Armed Forces personnel. The median age of study participants was 44 years with P25 and P75 respectively 38 and 47 years versus 40 years for the total Belgian Armed Forces personnel under 50 with P25 and P75 respectively 30 and 46 years. As older military personnel are more likely to do office work and to have military addresses, it is not surprising that participants in our study tended to be older. Because of the differences between the participants of the study and the Belgian Armed Forces personnel under 50, it may not be correct to apply our prevalence results to the military population under 50 as a whole. However, this does not affect the reliability of the statistical associations between rank/age and physical fitness as we had sufficient subjects in each subcategory. The use of self-reporting in our study for BMI, physical activity, smoking, and PFT could be seen as another limitation. However, different studies have shown that self-reporting of smoking status 20 and BMI 21 is accurate enough to use in epidemiological studies. The IPAQ short form showed acceptable to good results for both reliability and validity. 18 Self-reported values of PFT results are also adequate for military epidemiological studies involving larger sample size. 22 To counter any imbalance caused by self-reporting, these variables were categorized for the analysis. Our finding of an association between BMI and a poor performance on PFTs is consistent with 3 studies carried out in civilian population 2 4 and in military population, 15,16,23 but the association was not adjusted for physical activity in the five studies 2,4,15,16,23 and not adjusted for smoking in three studies. 2 4,16 Duvigneaud et al 3 confirmed the impaired cardiorespiratory fitness in obese adults compared to their lean counterparts after adjustment for physical activity, in a more age-diversified population (18 75 years). Crawford et al 17 only found an association between BF and passing the push-ups test but they didn t study the association between BF and the global PFT outcome, and they didn t adjust for smoking or physical activity. In a study evaluating a physical fitness screening test for army applicants before basic training, Wang et al 2 found a significant increase in estimated VO 2 max by reported leisure-time physical activity (LTPA) levels only for people who reported a high level of LTPA (³1,000 MET-min/wk) compared with those who reported no or less than 500 MET-min/wk of LTPA, but they didn t adjust for BMI, age, and smoking. Gubata et al 23 found that after adjustment for age and smoking status, those who met the physical activity recommendations were more likely to pass the physical fitness screening test, and that these findings were similar between applicants exceeding BF (greater than 30% BF for male) and those weight qualified. They didn t adjust the results for BF as they stratified the analysis according to BF limits. The adverse effect of smoking on PFT results was also found in a study in military population. 15,23 Macera et al 15 also found that smokers experienced a greater 904 MILITARY MEDICINE, Vol. 179, August 2014

5 rate of decrease in fitness over time after adjustment for age, BMI, and rank. One new interesting finding of our study was that only vigorous physical activity was associated with lower rate of PFT failure and nonparticipation. After adjustment for age, rank, smoking, BMI, walking, and vigorous physical activity, moderate physical activity was not associated anymore with passing the PFT. To our knowledge, this was the first study to examine simultaneously the impact of excess weight, smoking, and physical activity on the military PFT in a population of active duty military personnel. Our study also quantified this relationship and demonstrated the importance of performing frequent vigorous physical activity to pass the PFT. The conclusion of this study is that being a vigorously active nonsmoker with normal weight is related to a higher rate of passing the PFT. To maintain the military readiness of the Belgian Armed Forces, serious efforts should be made to encourage vigorous physical activity, smoking cessation, and weight control. Despite years of public health prevention campaigns against obesity, smoking, and physical inactivity conducted in the civilian society, all of these problems are still an important issue in the armed forces because they are strongly related with PFT failure and nonparticipation in the PFT. Instead of relying on civilian public health interventions, Belgian Defense should develop its own specific approaches to prevent weight gain, improve physical fitness, and influence smoking attitude. ACKNOWLEDGMENTS We are indebted to the participants of this study. The authors would like to thank Chief Warrant Officer Willy Lienard from the Unit of Epidemiology and Biostatistics of the Staff Department Wellbeing for designing the online survey and the database. This work was supported by the Belgian Armed Forces. 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