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Exercise during military training improves cardiovascular risk factors in young men
Atherosclerosis 216 (2011) 489–495
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Exercise during military training improves cardiovascular risk factors in young men Henna Cederberg a,∗ , Ilona Mikkola a,b , Jari Jokelainen a,c , Mauri Laakso a,c , Pirjo Härkönen d , Tiina Ikäheimo a , Markku Laakso e , Sirkka Keinänen-Kiukaanniemi a,c,f a
Institute of Health Sciences, Faculty of Medicine, University of Oulu, Finland Rovaniemi Health Centre, Rovaniemi, Finland Unit of General Practice, Oulu University Hospital, Oulu, Finland d Oulu Deaconess Institute/Diapolis Oy Research Unit, Oulu, Finland e Department of Medicine, University of Eastern Finland and Kuopio University Hospital, 70210 Kuopio, Finland f Oulu Health Center, Diabetes Unit, Saaristonkatu, Oulu, Finland b c
a r t i c l e
i n f o
Article history: Received 29 December 2010 Received in revised form 17 February 2011 Accepted 18 February 2011 Available online 24 February 2011 Keywords: Exercise Intervention Obesity Body composition Cardiovascular risk factors Risk reduction
a b s t r a c t Objective: Physical activity is a key component of lifestyle intervention but its independent contribution to weight loss and prevention of cardiovascular disease (CVD) remains unclear. We conducted a populationlevel follow-up study among young healthy Finnish men undergoing an intensive exercise intervention to examine the independent contribution of exercise to common CVD risk factors. Methods: A prospective study of 1112 young men with mean age of 19.3 years (range 19–28) undergoing military service with structured exercise training program. Endurance (12-min running test) and muscle fitness performance (MFI), body composition, blood pressure and biochemical measurements were obtained at baseline and follow-up (range 6–12 months). Results: Both endurance performance and MFI improved during follow-up (+170 m (SD 269) and 1.5 points (2.3), respectively, p < 0.001 for both). Both improvement in endurance and MFI performance correlated with a reduction in weight, body mass index, waist circumference, fat mass and percentage, visceral fat area (VFA) and diastolic blood pressure (p < 0.001 for all). Improvement in endurance performance also correlated with reduction in systolic blood pressure (p = 0.042), total and LDL cholesterol (p = 0.024 and p < 0.0001, respectively) and improvement in MFI with a reduction in triglyceride levels (p = 0.012). The 12-min running test correlated with changes in CVD risk factors better than did MFI. Associations between improved exercise performance and reduction in blood pressure, and changes in lipid levels were attributable to reduced weight and VFA. Conclusion: We observed that an isolated, intensive exercise intervention, especially endurance training, significantly improved CVD risk factor levels, attributable to weight loss and reduced visceral fat area. © 2011 Elsevier Ireland Ltd. All rights reserved.
1. Introduction Excess weight and weight gain during adolescence and adult life, even within the normal BMI range, significantly modifies the individual’s risk for cardiovascular disease (CVD) [1,2], and premature mortality [3]. Along with increased weight, a decrease in physical activity is observed among adolescents and young adults [4]. Sedentary behaviour is independently associated with increased metabolic risk factors [5]. The increasing prevalence of overweight, obesity and obesity-related disorders among young adults [6] high-
∗ Corresponding author at: University of Oulu, Faculty of Medicine, Institute of Health Sciences, P.O. Box 5000, FIN-90014 University of Oulu, Finland. Tel.: +358 8 537 5654; fax: +358 8 537 5661. E-mail address: henna.cederberg@oulu.fi (H. Cederberg). 0021-9150/$ – see front matter © 2011 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.atherosclerosis.2011.02.037
lights the need of effective tools to improve cardiovascular health of this age group. Lifestyle intervention with dietary modifications and exercise is a key tool in the treatment of overweight and obesity, and the prevention of type 2 diabetes and CVD [7]. The role of exercise may be more important in groups less receptive to nutritional advice, such as young men. The independent effects of physical activity and adiposity (‘fitness’ versus ‘fatness’) on the CVD risk factors are in a focus of intensive research [8]. Physical activity has been suggested to attenuate, but not eliminate, the adverse effects of obesity on cardiovascular health [3]. Most recent studies have investigated the effects of mild to moderate physical activity on cardiometabolic risk profile, while earlier studies have observed cardiovascular risk factor reduction in association with regular vigorous exercise [9]. The type of exercise, aerobic or endurance versus resistance train-
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ing, has different contributions to the reduction of cardiometabolic risk and modification of body composition [10], but large-scale population-based studies are lacking. Therefore, we conducted a large exercise intervention study in 1112 young men. We aimed (1) to determine whether exercise alone without dietary intervention can be used as an effective tool to reduce CVD risk factors in young adults, (2) to compare the efficacy of endurance and resistance training as modifiers of cardiovascular risk, and (3) to determine whether exercise per se, or weight loss, is associated with changes in CVD risk profile. 2. Methods 2.1. Research design A prospective study with an intensive exercise intervention and 6–12 month follow-up was performed on a population of young men entering military service at the Sodankylä Jaeger Brigade (67◦ N, 27◦ E), Finland. The population is representative of the age group since approximately 80% (25,000/year) of the male population complete military service. In 2005, 1467 men with mean age of 19.2 (SD 1.0 years, range 18–28) mainly from northern Finland attended the Brigade. All conscripts (1467) were invited to participate in the present study, and 79% (1160) were enrolled, all of Caucasian origin. Paired data of exercise and weight was available for 1112 men. Dropout was mainly caused by 140 conscripts who discontinued their military service due to physical or psychological reasons. These individuals did not significantly differ from the study cohort [11]. All participants gave a written consent to use the collected data for scientific purposes. The study protocol was approved by the Ethics Committee of Lapland Central Hospital, Rovaniemi, Finland. 2.2. Study protocol Data were collected at the beginning and at the end of military service. The follow-up period was 6, 9 or 12 months. The length of military service depends on the tasks and type of military training. Of all study subjects 58% served for 6 months (privates), 9% for 9 months (privates in need of special knowledge and skills) and 33% for 12 months (officers, non-commissioned officers, and privates in need of special professional skills). Participants answered questionnaires on background, demographics and smoking. Anthropometric, body composition, blood pressure and exercise performance measurements were taken and venous blood samples collected at baseline and follow-up. Weight (to nearest 0.1 kg) in light clothing and height (to nearest 0.5 cm) were measured. Waist circumference (cm) was measured midway between the lowest rib and the iliac crest. Body mass index (BMI) was calculated dividing body weight (kg) by the square of the height (m2 ). Body composition was analyzed by multifrequency bioelectric impedance analysis (BIA; InBody720, Biospace, Korea), as described in detail elsewhere [11]. The following body composition indices were derived: fat percentage (fat %), fat mass (FM, kg), skeletal mass (SM, kg), lean body mass (LBM, kg) and visceral fat area (VFA, cm2 ). VFA was calculated by the InBody720 which has been previously validated against a cross-sectional area of VFA measured by CT (Somaton Plus 24, Siemens, Germany). In the validation study including 332 subjects the correlation between these measurements was r = 0.922. Systolic and diastolic blood pressure levels were measured with an automated blood pressure measuring device (Omron Healthcare, model HEM-757, Japan) by a trained observer after 5–10 min in a sitting position. Venous blood samples were drawn by physicians or medical personnel after 12 h of overnight fasting, centrifuged immedi-
ately at 1500 × g for 15 min, and frozen at −20 ◦ C. Biochemical assessments were performed in the laboratory of Oulu Deaconess Institute by using commercially available, homogeneous enzymatic test (HDL cholesterol), enzymatic colorimetric test (triglyceride) and enzymatic tests (total and LDL cholesterol) (KonelabTM analyzers, Thermo Electron Oy, Vantaa, Finland) according to national quality standards. 2.3. Exercise performance Aerobic performance was measured by the Cooper 12-min running test [12]. The test was performed outdoors and controlled by educated supervisors. The test timing and circumstances were standardized. Participants were instructed to run 12 min with a maximal effort, and the test result was reported by the distance run with 10 m’ accuracy. The Cooper 12-min running test was developed for military use, and it provides a fairly good estimation for maximal oxygen uptake (VO2max ) without treadmill testing, which is considered as a “gold standard” (correlation coefficients are 0.84–0.92 with the treadmill VO2max ) [12,13]. Muscle fitness was measured by 5 tests: sit-ups, a back-muscle test (testing endurance of abdominal, back, and hip-flexor muscles), push and pull-ups (testing upper extremities), and standing long jump (testing explosive muscle strength), as described in detail elsewhere [14]. Participants were asked to perform a maximum number of repetitions of concentric muscle actions possible during 60 s, with a 5 min break for recovery between each component. Results were recorded to the accuracy of the nearest repetition and for the long jump, to the nearest 1 cm. Muscle fitness performance was graded for each component (0 = poor, 1 = satisfactory, 2 = good, 3 = very good), and a sum of scores of individual components was calculated to determine the total muscle fitness index (MFI, 0–4 = poor, 5–8 = satisfactory, 9–12 = good and 13–15 = very good). 2.4. Amount of physical exercise Physical activity during military training consists of exercise training (includes running, Nordic walking, strength training, martial arts, orienteering, swimming, cross-country skiing, and recovery training), as well as combat training and marching. The estimated amount of physical activity during the 8-week basic training period in the beginning of the military service corresponds on average to approximately 4 h of sports-related physical activity and 12 h of military-related physical training (such as combat training and marching) per week. After the basic training period, the total amount of physical activity varies slightly during subsequent special training and unit training periods, and also depending on the branch of service. 2.5. Statistical analysis Continuous variables are presented as mean ± standard deviation (SD) or range. Paired t-test was used to evaluate the difference between mean values at baseline and at follow-up. Associations between changes in dependent and independent variables (change in weight, VFA, 12-min running test or MFI) were assessed by Pearson correlation coefficients. Linearity assumptions of the model were evaluated by means of standard scatter plots, with linear and nonlinear fit. Multivariate linear regression analysis, adjusting for length of service, smoking, and baseline value of the independent variable, was used to estimate the association of independent variables with the dependent variables. A change in exercise performance as an independent variable was adjusted by change in weight and vice versa. p < 0.05 was considered statistically sig-
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Fig. 1. Associations between change () in weight and endurance performance (12-min running test), and changes in cardiovascular risk factors. Multiple linear regression analysis for the association between change in weight and CVD risk factor, and as adjusted for exercise performance (MFI, muscle fitness index). Association between change in 12 min running test and CVD risk factor, and as adjusted for change in weight. (R and P values are in parentheses.)
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Table 1 Characteristics of the cohort at baseline and absolute changes in cardiovascular risk factors from baseline to follow-up. Values are mean (SD), unless stated otherwise. Variable
n
Baseline
Change from baseline to follow-up
P-value
Age (years) (mean, range) Weight (kg) (mean, range) BMI (kg/m2 ) (mean, range) Waist circumference (cm) Fat mass (kg) Fat % Lean body mass (kg) Skeletal mass (kg) Visceral Fat Area (cm2 ) Systolic blood pressure (mmHg) Diastolic blood pressure (mmHg) Total serum cholesterol (mmol/L) LDL-cholesterol (mmol/L) HDL-cholesterol (mmol/L) Triglycerides (mmol/L) 12-min running test (m) (mean, range) Muscle fitness index (points) (mean, range)
1070 1070 1070 1056 1030 1030 1030 1030 1030 1060 1061 998 986 998 1000 1146 1137
19.3 (18–28) 75.1 (47.2–140.0) 23.9 (16.3–46.0) 81.6 (10.2) 13.4 (9.2) 16.7 (8.2) 58.3 (6.9) 34.9 (4.4) 65.7 (50.8) 128.8 (13.5) 69.8 (9.8) 3.89 (0.83) 2.23 (0.74) 1.29 (0.30) 0.79 (0.36) 2482 (1000–3910) 8.0 (1–15)
−0.42 (5.19) −0.30 (1.69) 0.10 (5.8) −1.3 (4.7) −1.1 (4.6) 0.8 (2.4) 0.6 (1.5) −28.4 (33.3) −2.1 (13.2) 2.0 (9.9) 0.43 (0.79) 0.18 (0.64) 0.08 (0.26) 0.42 (0.76) 170 (269) 1.5 (2.3)
0.008 <0.001 0.589 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001
Table 2 Pearson correlations between changes () in weight, visceral fat area (VFA), 12-min running test (Cooper test) and muscle fitness index (MFI), and body composition and cardiovascular risk factors (P values are in parentheses). Change in variable
Weight
VFA
Cooper test
MFI
Weight (kg) BMI (kg/m2 ) Waist circumference (cm) Fat mass (kg) Fat % Lean body mass (kg) Skeletal mass (kg) Visceral fat area (cm2 ) Diastolic blood pressure (mmHg) Systolic blood pressure (mmHg) Total serum cholesterol (mmol/L) LDL-cholesterol (mmol/L) HDL-cholesterol (mmol/L) Triglycerides (mmol/L) 12-min running test (m) Muscle fitness index (points)
1.000 0.977 (<0.001) 0.81 (<0.001) 0.877 (<0.001) 0.779 (<0.001) 0.435 (<0.001) 0.459 (<0.001) 0.645 (<0.001) 0.203 (<0.001) 0.155 (<0.001) 0.251 (<0.001) 0.339 (<0.001) −0.165 (<0.001) 0.043 (0.174) −0.31 (<0.001) −0.173 (<0.001)
0.645 (<0.001) 0.664 (<0.001) 0.394 (<0.001) 0.695 (<0.001) 0.631 (<0.001) 0.042 (0.176) 0.073 (0.018) 1.000 0.248 (<0.001) 0.106 (<0.001) 0.128 (<0.001) 0.236 (<0.001) −0.152 (<0.001) −0.058 (0.073) −0.469 (<0.001) −0.181 (<0.001)
−0.31 (<0.001) −0.305 (<0.001) −0.183 (<0.001) −0.296 (<0.001) −0.266 (<0.001) −0.093 (0.004) −0.114 (<0.001) −0.469 (<0.001) −0.217 (<0.001) −0.065 (0.042) −0.074 (0.024) −0.115 (<0.001) 0.04 (0.219) 0.029 (0.370) 1.000 0.216 (<0.001)
−0.173 (<0.001) −0.163 (<0.001) −0.116 (<0.001) −0.178 (<0.001) −0.187 (<0.001) −0.013 (0.690) −0.02 (0.547) −0.181 (<0.001) −0.155 (<0.001) −0.005 (0.887) −0.059 (0.0770) −0.063 (0.059) 0.031 (0.349) −0.083 (0.012) 0.216 (<0.001) 1.000
Table 3 Associations of changes in weight, visceral adiposity, aerobic and muscle fitness, with changes in cardiovascular risk factors. Effect size is B coefficient (standard error) and standardized beta (ˇ), calculated by linear regression. Analyses were adjusted for baseline value of the independent variable, length of follow-up and smoking. Changes in 12-min running test and muscle fitness index were adjusted for changes in weight. Changes in weight and visceral fat were adjusted for change in 12-min running test and muscle fitness index. VFA = visceral fat area, Cooper test = 12-min running test, MFI = muscle fitness index. Variable
Weight B (SE)
VFA ˇ
Crude Systolic blood pressure (mmHg) 0.394 (0.077) 0.155 Diastolic blood pressure (mmHg) 0.388 (0.058) 0.203 Total serum cholesterol (mmol/L)* 0.379 (0.047) 0.251 LDL-cholesterol (mmol/L)* 0.417 (0.037) 0.339 HDL-cholesterol (mmol/L)* −0.081 (0.016) −0.165 Triglycerides (mmol/L)* 0.062 (0.046) 0.043 Adjusted Systolic blood pressure (mmHg) 0.722 (0.113) 0.275 Diastolic blood pressure (mmHg) 0.217 (0.083) 0.110 Total serum cholesterol (mmol/L)* 0.485 (0.067) 0.308 LDL-cholesterol (mmol/L)* 0.426 (0.053) 0.340 HDL-cholesterol (mmol/L)* −0.056 (0.023) −0.111 Triglycerides (mmol/L)* 0.202 (0.065) 0.139
P value B (SE)
Cooper test ˇ
P value B (SE)
MFI ˇ
P value B (SE)
ˇ
P value
<0.001 0.042 (0.012) 0.106 <0.001 0.074 (0.009) 0.248 <0.001 0.030 (0.008) 0.128 <0.001 0.046 (0.006) 0.236 <0.001 −0.001 (0.002) −0.152 0.174 −0.013 (0.007) −0.058
<0.001 <0.001 <0.001 <0.001 <0.001 0.073
−0.031 (0.016) −0.083 (0.012) −0.023 (0.010) −0.029 (0.001) 0.004 (0.003) 0.008 (0.009)
−0.065 0.042 −0.026 (0.187) −0.005 0.887 −0.217 <0.001 −0.676 (0.138) −0.155 <0.001 −0.074 0.024 −0.199 (0.112) −0.059 0.077 −0.115 <0.001 −0.174 (0.092) −0.063 0.059 0.040 0.219 0.034 (0.037) 0.031 0.349 0.029 0.370 −0.264 (0.105) −0.083 0.012
<0.001 0.070 (0.024) 0.172 0.009 0.045 (0.017) 0.144 <0.001 0.042 (0.015) 0.173 <0.001 0.038 (0.012) 0.192 0.013 −0.004 (0.005) −0.048 0.002 0.007 (0.001) 0.029
0.003 0.010 0.004 0.001 0.416 0.631
−0.012 (0.020) −0.041 (0.015) −0.013 (0.012) −0.004 (0.001) −0.002 (0.004) −0.012 (0.012)
−0.024 −0.109 −0.041 −0.017 −0.019 −0.042
0.546 0.005 0.294 0.660 0.639 0.302
−0.019 (0.212) −0.449 (0.156) −0.173 (0.126) −0.053 (0.101) −0.037 (0.042) −0.363 (0.123)
−0.003 −0.102 −0.051 −0.019 −0.033 −0.113
0.929 0.004 0.169 0.596 0.379 0.003
B coefficients (SE) are for change per one unit for weight, VFA and MFI; for 10 m change in the 12 min running test (Cooper test), * and for 0.1 mmol/L change in lipids.
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nificant. Statistical analysis was performed using SAS 9.1.3. for Windows (SAS Institute Inc. Gary NC). 3. Results 3.1. Total changes in exercise performance, body composition and CVD risk profile Anthropometric characteristics and cardiovascular risk profile of the cohort at baseline are shown in Table 1. At baseline the participants had a normal mean BMI (23.9 kg/m2 , range from 16.3 to 46.0 kg/m2 ). An improvement in both aerobic capacity and muscle performance was observed during the follow-up (Table 1). Mean aerobic performance in the 12-min running test at baseline was 2482 m (range 1000–3910) and improved by 170 m (SD 269) during the follow-up. Mean muscle fitness index at baseline was 8.0 points (range 1–15) and improved by 1.5 points (SD 2.3). During the follow-up, significant reductions were observed in weight (p = 0.008), fat mass, fat percentage, and VFA (p < 0.0001 for all) (Table 1). Systolic blood pressure decreased and HDL cholesterol increased significantly (p < 0.001 for both). In contrast, diastolic blood pressure, total and LDL cholesterol and triglycerides increased. 3.2. Association between weight loss, body composition and CVD status Weight loss strongly correlated with the reduction of BMI, waist circumference, FM, fat %, and VFA (Table 2). Weight loss significantly correlated with a decrease in both systolic and diastolic blood pressure (r = 0.203 and 0.155, respectively, p < 0.001), with a decrease in total and LDL cholesterol and triglycerides, and an increase in HDL cholesterol (p < 0.0001 for all). Decrease in VFA correlated with reductions in blood pressure and lipid levels similarly to those of weight loss (p < 0.001 for all), with the exception of triglycerides (NS). 3.3. Associations between the changes in exercise performance, body composition and CVD status Improvement in endurance and muscle performance significantly correlated with weight loss, decrease in waist circumference, and decreases in FM, fat % and VFA (p < 0.0001 for all) (Table 2). Correlations for the change in the 12-min running test were substantially higher than for the change in MFI. Decrease in blood pressure levels, particularly systolic blood pressure, correlated more strongly with the improvement in endurance performance than with muscle performance. Compared to the improvement in muscle performance, improvement in 12min running test correlated more strongly with improvement in lipid parameters. 3.4. Comparison of the effects of weight loss and exercise on CVD risk factors Associations between the changes in weight, endurance performance, blood pressure levels, and lipids were linear (data not shown), and therefore linear regression analysis was applied in the subsequent statistical analysis. Multiple linear regression analysis showed that the improvement in blood pressure and lipid levels with increased aerobic capacity was attributable to weight loss (Fig. 1). Additional adjustment for changes in either aerobic or muscle performance did not alter the effect of weight loss on CVD risk factors. The association of weight loss with changes in blood pressure and lipid levels
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remained significant after the adjustment for baseline weight, changes in both exercise parameters, length of follow-up and smoking (Table 3). The effects of the reduction in VFA on changes in blood pressure and lipid levels were smaller than that of weight loss (Table 3), but remained significant for blood pressure, LDL and total cholesterol levels after adjustment for confounding factors. Effects of the improvement in 12-min running test as a modifier of CVD risk factors were small, and were significant only for diastolic blood pressure after the adjustment for confounding factors. Increase in muscle performance was associated with the reduction of diastolic blood pressure and triglyceride levels, even after the adjustment for confounding factors.
4. Discussion In our prospective study of 1112 young Finnish men an intensive exercise program during military service significantly improved CVD risk profile. Particularly beneficial was aerobic exercise resulting in the reduction of visceral fat area. The beneficial changes in body composition and CVD risk factors were attributable to an exercise program without a dietary intervention. Therefore, this study provides population-level evidence for an independent contribution of exercise intervention to the improvement of CVD risk factors levels. Both endurance and muscle fitness performance improved during the 6–12 months exercise intervention, and both of them significantly reduced weight, central adiposity, total fat mass, and visceral fat area. Weight loss and beneficial body composition changes were greater in association with an improvement in endurance performance than with an improvement in muscle fitness performance. Similar body composition changes have previously been reported with moderate to vigorous exercise [15]. While the mean total weight loss in our cohort was modest, it was more pronounced in the overweight and obese young men (−3.2 kg for BMI of 25–29.9 kg/m2 , and −8.9 kg for BMI of ≥30 kg/m2 , respectively) [11]. The overall improvement in physical performance in our cohort was relatively modest, reflecting the heterogeneous physical activity background of study participants entering the military service. Similar studies from other military cohorts with similar methods are lacking, data are conflicting and thus direct comparison of the changes in physical performance is difficult. Physical activity is known to be protective against premature mortality and morbidity [16], but with most lifestyle intervention studies combining diet with weight loss and physical activity [17], the independent contribution of physical activity to improved health outcomes has remained unclear. In our study both weight loss and reduction in central adiposity, as well as improvement in physical performance were associated with a decrease in blood pressure levels and favourable changes in the lipid profile. The effect of improved exercise performance on the lowering of blood pressure and altering lipids was, however, attributable mainly to weight loss and reduction of VFA. This is most likely due to increased energy expenditure induced by exercise. Studies regarding changes in individual CVD risk factors in response to physical activity have been controversial. Exercise has not lowered blood pressure in some of the previous studies [18,19]. However, a meta-analysis by Whelton et al., reported that aerobic exercise lowered blood pressure levels both in hypertensive and normotensive individuals [20]. In our exercise-only intervention study of non-diabetic young men, we demonstrated that improvement in aerobic performance was associated with a reduction in abdominal obesity and blood pressure levels. Previous exercise intervention studies have observed an overall beneficial effect on the lipid profile, particularly with respect to
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HDL cholesterol and also triglycerides, but the effect has been variable and overall small across the studies. The dose and intensity of exercise required to achieve the desired changes in the lipid profile remain unclear [21]. Furthermore, it has also been unclear as to whether these effects are independent of the changes in body composition. In our study, we observed an increase in HDL and decrease in total and LDL cholesterol levels, which were attributable to weight loss and reduction of visceral fat mass. Our findings suggest that the effect of exercise on lipid profile is mediated by changes in weight and body composition. Central adiposity provides the key link between the improvement in exercise performance and reduction in CVD risk factors. Visceral fat has an independent curvilinear association with mortality [22]. Compared to total fat mass, high amounts of visceral fat have been associated more strongly with blood pressure, the HDL/total cholesterol ratio and insulin resistance [23]. Central adiposity has also been linked with elevated systolic blood pressure levels in the Nurses’ Health Study, and decreased visceral fat has been associated with a reduction in blood pressure [24]. Obesity and particularly visceral fat are associated with qualitative and quantitative changes in lipids and lipoproteins, such as increases in total cholesterol, very low-density lipoproteins (VLDL), small dense LDL particles, triglycerides and decreases in high-density lipoprotein (HDL) cholesterol levels [25]. Our study is in agreement with these findings showing that exercise intervention reduced VFA and resulted in favourable changes in lipid and lipoprotein levels. Diet is important for both weight loss and changes in cardiovascular risk factors, particularly lipid profile [26]. Our study was carried out in a military setting and did not include a dietary intervention. The intended content of energy in the food served to every conscript by the military forces is 3200–3600 kcal/day, of which 30–35% consist of fat [27]. Hence, the importance of exercise as a modifier of CVD risk factors is highlighted in this setting with no caloric restriction. Caloric restriction has been reported to have an independent effect and also a combined effect with exercise to improve CVD risk in healthy non-obese individuals [28]. Reports from the United States and Scandinavia have shown an increase in the prevalence of obesity among men entering military service [29,30], and a simultaneous gradual decline in aerobic fitness in the past decade [14]. In contrast, our results demonstrate weight loss, favourable changes in body composition and cardiovascular risk factor levels in association with improved exercise performance during the military service. Albeit these changes on average were modest, they were pronounced in overweight and obese men, and if maintained, these relatively small changes could potentially translate into substantial health benefits over time. The challenge, however, is the maintenance of the required levels of physical activity beyond the intervention period. This study has several strengths. It was a large intervention study to investigate the independent contribution of exercise on CVD risk factor levels among healthy young adults. The cohort was a representative sample of healthy Finnish male adults. Exercise performance was objectively measured both for endurance and muscle fitness. Moreover, the main meals and living circumstances were standardized for all participants. However, the study has limitations. We did not have a control group due to the study design. VFA was evaluated by InBody720 (BIA). More studies are needed to validate this method in different ethnic groups. Inevitable changes in diet and environment associated with military service may have had some effects on cardiovascular risk factors or body weight. Approximately 10% of the age group are exempt from military service during medical examination due to physical or mental reasons, and therefore it is likely that the most obese are not represented in our cohort. Our results are also limited to men, as the number of women entering military service in Finland is small and therefore women were excluded from statistical analysis.
In conclusion, our large study of young healthy men shows that high amounts of exercise, and particularly endurance training, were associated with reductions in blood pressure levels and favourable changes in the lipid profile during a 6–12-month follow-up period. The changes were attributable to weight loss and the reduction of abdominal fat area. Thus, exercise resulting in weight loss provides a successful tool to reduce the epidemic of obesity and to improve CVD risk factor levels among young men. Conflict of interest The authors have no conflict of interest relevant to the article. Acknowledgements The authors would like to thank Medical Colonel, M.D. Ph.D. Ari Peitso from the Finnish Defence Forces for his assistance with the study. Author Ilona Mikkola would like to thank the Finnish Cultural Foundation for its support to the study. References [1] Berenson GS, Srinivasan SR, Bao W, et al. Association between multiple cardiovascular risk factors and atherosclerosis in children and young adults. The Bogalusa Heart Study. N Engl J Med 1998;338:1650–6. [2] Olshansky SJ, Passaro DJ, Hershow RC, et al. A potential decline in life expectancy in the United States in the 21st century. N Engl J Med 2005;352:1138–45. [3] Hu FB, Willett WC, Li T, et al. Adiposity as compared with physical activity in predicting mortality among women. N Engl J Med 2004;351:2694– 703. [4] Tammelin T, Ekelund U, Remes J, et al. Physical activity and sedentary behaviors among Finnish youth. Med Sci Sports Exerc 2007;39:1067–74. [5] Healy GN, Wijndaele K, Dunstan DW, et al. Objectively measured sedentary time, physical activity, and metabolic risk: the Australian Diabetes, Obesity and Lifestyle Study (AusDiab). Diabetes Care 2008;31:369–71. [6] James PT, Rigby N, Leach R. The obesity epidemic, metabolic syndrome and future prevention strategies. Eur J Cardiovasc Prev Rehabil 2004;11:3–8. [7] Tuomilehto J, Lindstrom J, Eriksson JG, et al. Prevention of type 2 diabetes mellitus by changes in lifestyle among subjects with impaired glucose tolerance. N Engl J Med 2001;344:1343–50. [8] Blair SN, Church TS. The fitness, obesity, and health equation: is physical activity the common denominator? JAMA 2004;292:1232–4. [9] Oberman A. Healthy exercise. West J Med 1984;141:864–71. [10] Ko GT. Short-term effects after a 3-month aerobic or anaerobic exercise programme in Hong Kong Chinese. Diabetes Nutr Metab 2004;17:124–7. [11] Mikkola I, Jokelainen JJ, Timonen MJ, et al. Physical activity and body composition changes during military service. Med Sci Sports Exerc 2009;41:1735– 42. [12] Cooper KH. A means of assessing maximal oxygen intake. Correlation between field and treadmill testing. JAMA 1968;203:201–4. [13] Grant S, Corbett K, Amjad AM, et al. A comparison of methods of predicting maximum oxygen uptake. Br J Sports Med 1995;29:147–52. [14] Santtila M, Kyrolainen H, Vasankari T, et al. Physical fitness profiles in young Finnish men during the years 1975–2004. Med Sci Sports Exerc 2006;38:1990–4. [15] Slentz CA, Houmard JA, Kraus WE. Exercise, abdominal obesity, skeletal muscle, and metabolic risk: evidence for a dose response. Obesity (Silver Spring) 2009;17(Suppl. 3):S27–33. [16] Wei M, Kampert JB, Barlow CE, et al. Relationship between low cardiorespiratory fitness and mortality in normal-weight, overweight, and obese men. JAMA 1999;282:1547–53. [17] Yates T, Khunti K, Bull F, et al. The role of physical activity in the management of impaired glucose tolerance: a systematic review. Diabetologia 2007;50:1116–26. [18] Church TS, Earnest CP, Skinner JS, et al. Effects of different doses of physical activity on cardiorespiratory fitness among sedentary, overweight or obese postmenopausal women with elevated blood pressure: a randomized controlled trial. JAMA 2007;297:2081–91. [19] Ilanne-Parikka P, Laaksonen DE, Eriksson JG, et al. Leisure-time physical activity and the metabolic syndrome in the Finnish diabetes prevention study. Diabetes Care 2010;33:1610–7. [20] Whelton SP, Chin A, Xin X, et al. Effect of aerobic exercise on blood pressure: a meta-analysis of randomized, controlled trials. Ann Intern Med 2002;136:493–503. [21] Kraus WE, Slentz CA. Exercise training, lipid regulation, and insulin action: a tangled web of cause and effect. Obesity (Silver Spring) 2009;17(Suppl. 3):S21–6.
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Atherosclerosis journal homepage: www.elsevier.com/locate/atherosclerosis
Exercise during military training improves cardiovascular risk factors in young men Henna Cederberg a,∗ , Ilona Mikkola a,b , Jari Jokelainen a,c , Mauri Laakso a,c , Pirjo Härkönen d , Tiina Ikäheimo a , Markku Laakso e , Sirkka Keinänen-Kiukaanniemi a,c,f a
Institute of Health Sciences, Faculty of Medicine, University of Oulu, Finland Rovaniemi Health Centre, Rovaniemi, Finland Unit of General Practice, Oulu University Hospital, Oulu, Finland d Oulu Deaconess Institute/Diapolis Oy Research Unit, Oulu, Finland e Department of Medicine, University of Eastern Finland and Kuopio University Hospital, 70210 Kuopio, Finland f Oulu Health Center, Diabetes Unit, Saaristonkatu, Oulu, Finland b c
a r t i c l e
i n f o
Article history: Received 29 December 2010 Received in revised form 17 February 2011 Accepted 18 February 2011 Available online 24 February 2011 Keywords: Exercise Intervention Obesity Body composition Cardiovascular risk factors Risk reduction
a b s t r a c t Objective: Physical activity is a key component of lifestyle intervention but its independent contribution to weight loss and prevention of cardiovascular disease (CVD) remains unclear. We conducted a populationlevel follow-up study among young healthy Finnish men undergoing an intensive exercise intervention to examine the independent contribution of exercise to common CVD risk factors. Methods: A prospective study of 1112 young men with mean age of 19.3 years (range 19–28) undergoing military service with structured exercise training program. Endurance (12-min running test) and muscle fitness performance (MFI), body composition, blood pressure and biochemical measurements were obtained at baseline and follow-up (range 6–12 months). Results: Both endurance performance and MFI improved during follow-up (+170 m (SD 269) and 1.5 points (2.3), respectively, p < 0.001 for both). Both improvement in endurance and MFI performance correlated with a reduction in weight, body mass index, waist circumference, fat mass and percentage, visceral fat area (VFA) and diastolic blood pressure (p < 0.001 for all). Improvement in endurance performance also correlated with reduction in systolic blood pressure (p = 0.042), total and LDL cholesterol (p = 0.024 and p < 0.0001, respectively) and improvement in MFI with a reduction in triglyceride levels (p = 0.012). The 12-min running test correlated with changes in CVD risk factors better than did MFI. Associations between improved exercise performance and reduction in blood pressure, and changes in lipid levels were attributable to reduced weight and VFA. Conclusion: We observed that an isolated, intensive exercise intervention, especially endurance training, significantly improved CVD risk factor levels, attributable to weight loss and reduced visceral fat area. © 2011 Elsevier Ireland Ltd. All rights reserved.
1. Introduction Excess weight and weight gain during adolescence and adult life, even within the normal BMI range, significantly modifies the individual’s risk for cardiovascular disease (CVD) [1,2], and premature mortality [3]. Along with increased weight, a decrease in physical activity is observed among adolescents and young adults [4]. Sedentary behaviour is independently associated with increased metabolic risk factors [5]. The increasing prevalence of overweight, obesity and obesity-related disorders among young adults [6] high-
∗ Corresponding author at: University of Oulu, Faculty of Medicine, Institute of Health Sciences, P.O. Box 5000, FIN-90014 University of Oulu, Finland. Tel.: +358 8 537 5654; fax: +358 8 537 5661. E-mail address: henna.cederberg@oulu.fi (H. Cederberg). 0021-9150/$ – see front matter © 2011 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.atherosclerosis.2011.02.037
lights the need of effective tools to improve cardiovascular health of this age group. Lifestyle intervention with dietary modifications and exercise is a key tool in the treatment of overweight and obesity, and the prevention of type 2 diabetes and CVD [7]. The role of exercise may be more important in groups less receptive to nutritional advice, such as young men. The independent effects of physical activity and adiposity (‘fitness’ versus ‘fatness’) on the CVD risk factors are in a focus of intensive research [8]. Physical activity has been suggested to attenuate, but not eliminate, the adverse effects of obesity on cardiovascular health [3]. Most recent studies have investigated the effects of mild to moderate physical activity on cardiometabolic risk profile, while earlier studies have observed cardiovascular risk factor reduction in association with regular vigorous exercise [9]. The type of exercise, aerobic or endurance versus resistance train-
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ing, has different contributions to the reduction of cardiometabolic risk and modification of body composition [10], but large-scale population-based studies are lacking. Therefore, we conducted a large exercise intervention study in 1112 young men. We aimed (1) to determine whether exercise alone without dietary intervention can be used as an effective tool to reduce CVD risk factors in young adults, (2) to compare the efficacy of endurance and resistance training as modifiers of cardiovascular risk, and (3) to determine whether exercise per se, or weight loss, is associated with changes in CVD risk profile. 2. Methods 2.1. Research design A prospective study with an intensive exercise intervention and 6–12 month follow-up was performed on a population of young men entering military service at the Sodankylä Jaeger Brigade (67◦ N, 27◦ E), Finland. The population is representative of the age group since approximately 80% (25,000/year) of the male population complete military service. In 2005, 1467 men with mean age of 19.2 (SD 1.0 years, range 18–28) mainly from northern Finland attended the Brigade. All conscripts (1467) were invited to participate in the present study, and 79% (1160) were enrolled, all of Caucasian origin. Paired data of exercise and weight was available for 1112 men. Dropout was mainly caused by 140 conscripts who discontinued their military service due to physical or psychological reasons. These individuals did not significantly differ from the study cohort [11]. All participants gave a written consent to use the collected data for scientific purposes. The study protocol was approved by the Ethics Committee of Lapland Central Hospital, Rovaniemi, Finland. 2.2. Study protocol Data were collected at the beginning and at the end of military service. The follow-up period was 6, 9 or 12 months. The length of military service depends on the tasks and type of military training. Of all study subjects 58% served for 6 months (privates), 9% for 9 months (privates in need of special knowledge and skills) and 33% for 12 months (officers, non-commissioned officers, and privates in need of special professional skills). Participants answered questionnaires on background, demographics and smoking. Anthropometric, body composition, blood pressure and exercise performance measurements were taken and venous blood samples collected at baseline and follow-up. Weight (to nearest 0.1 kg) in light clothing and height (to nearest 0.5 cm) were measured. Waist circumference (cm) was measured midway between the lowest rib and the iliac crest. Body mass index (BMI) was calculated dividing body weight (kg) by the square of the height (m2 ). Body composition was analyzed by multifrequency bioelectric impedance analysis (BIA; InBody720, Biospace, Korea), as described in detail elsewhere [11]. The following body composition indices were derived: fat percentage (fat %), fat mass (FM, kg), skeletal mass (SM, kg), lean body mass (LBM, kg) and visceral fat area (VFA, cm2 ). VFA was calculated by the InBody720 which has been previously validated against a cross-sectional area of VFA measured by CT (Somaton Plus 24, Siemens, Germany). In the validation study including 332 subjects the correlation between these measurements was r = 0.922. Systolic and diastolic blood pressure levels were measured with an automated blood pressure measuring device (Omron Healthcare, model HEM-757, Japan) by a trained observer after 5–10 min in a sitting position. Venous blood samples were drawn by physicians or medical personnel after 12 h of overnight fasting, centrifuged immedi-
ately at 1500 × g for 15 min, and frozen at −20 ◦ C. Biochemical assessments were performed in the laboratory of Oulu Deaconess Institute by using commercially available, homogeneous enzymatic test (HDL cholesterol), enzymatic colorimetric test (triglyceride) and enzymatic tests (total and LDL cholesterol) (KonelabTM analyzers, Thermo Electron Oy, Vantaa, Finland) according to national quality standards. 2.3. Exercise performance Aerobic performance was measured by the Cooper 12-min running test [12]. The test was performed outdoors and controlled by educated supervisors. The test timing and circumstances were standardized. Participants were instructed to run 12 min with a maximal effort, and the test result was reported by the distance run with 10 m’ accuracy. The Cooper 12-min running test was developed for military use, and it provides a fairly good estimation for maximal oxygen uptake (VO2max ) without treadmill testing, which is considered as a “gold standard” (correlation coefficients are 0.84–0.92 with the treadmill VO2max ) [12,13]. Muscle fitness was measured by 5 tests: sit-ups, a back-muscle test (testing endurance of abdominal, back, and hip-flexor muscles), push and pull-ups (testing upper extremities), and standing long jump (testing explosive muscle strength), as described in detail elsewhere [14]. Participants were asked to perform a maximum number of repetitions of concentric muscle actions possible during 60 s, with a 5 min break for recovery between each component. Results were recorded to the accuracy of the nearest repetition and for the long jump, to the nearest 1 cm. Muscle fitness performance was graded for each component (0 = poor, 1 = satisfactory, 2 = good, 3 = very good), and a sum of scores of individual components was calculated to determine the total muscle fitness index (MFI, 0–4 = poor, 5–8 = satisfactory, 9–12 = good and 13–15 = very good). 2.4. Amount of physical exercise Physical activity during military training consists of exercise training (includes running, Nordic walking, strength training, martial arts, orienteering, swimming, cross-country skiing, and recovery training), as well as combat training and marching. The estimated amount of physical activity during the 8-week basic training period in the beginning of the military service corresponds on average to approximately 4 h of sports-related physical activity and 12 h of military-related physical training (such as combat training and marching) per week. After the basic training period, the total amount of physical activity varies slightly during subsequent special training and unit training periods, and also depending on the branch of service. 2.5. Statistical analysis Continuous variables are presented as mean ± standard deviation (SD) or range. Paired t-test was used to evaluate the difference between mean values at baseline and at follow-up. Associations between changes in dependent and independent variables (change in weight, VFA, 12-min running test or MFI) were assessed by Pearson correlation coefficients. Linearity assumptions of the model were evaluated by means of standard scatter plots, with linear and nonlinear fit. Multivariate linear regression analysis, adjusting for length of service, smoking, and baseline value of the independent variable, was used to estimate the association of independent variables with the dependent variables. A change in exercise performance as an independent variable was adjusted by change in weight and vice versa. p < 0.05 was considered statistically sig-
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Fig. 1. Associations between change () in weight and endurance performance (12-min running test), and changes in cardiovascular risk factors. Multiple linear regression analysis for the association between change in weight and CVD risk factor, and as adjusted for exercise performance (MFI, muscle fitness index). Association between change in 12 min running test and CVD risk factor, and as adjusted for change in weight. (R and P values are in parentheses.)
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Table 1 Characteristics of the cohort at baseline and absolute changes in cardiovascular risk factors from baseline to follow-up. Values are mean (SD), unless stated otherwise. Variable
n
Baseline
Change from baseline to follow-up
P-value
Age (years) (mean, range) Weight (kg) (mean, range) BMI (kg/m2 ) (mean, range) Waist circumference (cm) Fat mass (kg) Fat % Lean body mass (kg) Skeletal mass (kg) Visceral Fat Area (cm2 ) Systolic blood pressure (mmHg) Diastolic blood pressure (mmHg) Total serum cholesterol (mmol/L) LDL-cholesterol (mmol/L) HDL-cholesterol (mmol/L) Triglycerides (mmol/L) 12-min running test (m) (mean, range) Muscle fitness index (points) (mean, range)
1070 1070 1070 1056 1030 1030 1030 1030 1030 1060 1061 998 986 998 1000 1146 1137
19.3 (18–28) 75.1 (47.2–140.0) 23.9 (16.3–46.0) 81.6 (10.2) 13.4 (9.2) 16.7 (8.2) 58.3 (6.9) 34.9 (4.4) 65.7 (50.8) 128.8 (13.5) 69.8 (9.8) 3.89 (0.83) 2.23 (0.74) 1.29 (0.30) 0.79 (0.36) 2482 (1000–3910) 8.0 (1–15)
−0.42 (5.19) −0.30 (1.69) 0.10 (5.8) −1.3 (4.7) −1.1 (4.6) 0.8 (2.4) 0.6 (1.5) −28.4 (33.3) −2.1 (13.2) 2.0 (9.9) 0.43 (0.79) 0.18 (0.64) 0.08 (0.26) 0.42 (0.76) 170 (269) 1.5 (2.3)
0.008 <0.001 0.589 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001
Table 2 Pearson correlations between changes () in weight, visceral fat area (VFA), 12-min running test (Cooper test) and muscle fitness index (MFI), and body composition and cardiovascular risk factors (P values are in parentheses). Change in variable
Weight
VFA
Cooper test
MFI
Weight (kg) BMI (kg/m2 ) Waist circumference (cm) Fat mass (kg) Fat % Lean body mass (kg) Skeletal mass (kg) Visceral fat area (cm2 ) Diastolic blood pressure (mmHg) Systolic blood pressure (mmHg) Total serum cholesterol (mmol/L) LDL-cholesterol (mmol/L) HDL-cholesterol (mmol/L) Triglycerides (mmol/L) 12-min running test (m) Muscle fitness index (points)
1.000 0.977 (<0.001) 0.81 (<0.001) 0.877 (<0.001) 0.779 (<0.001) 0.435 (<0.001) 0.459 (<0.001) 0.645 (<0.001) 0.203 (<0.001) 0.155 (<0.001) 0.251 (<0.001) 0.339 (<0.001) −0.165 (<0.001) 0.043 (0.174) −0.31 (<0.001) −0.173 (<0.001)
0.645 (<0.001) 0.664 (<0.001) 0.394 (<0.001) 0.695 (<0.001) 0.631 (<0.001) 0.042 (0.176) 0.073 (0.018) 1.000 0.248 (<0.001) 0.106 (<0.001) 0.128 (<0.001) 0.236 (<0.001) −0.152 (<0.001) −0.058 (0.073) −0.469 (<0.001) −0.181 (<0.001)
−0.31 (<0.001) −0.305 (<0.001) −0.183 (<0.001) −0.296 (<0.001) −0.266 (<0.001) −0.093 (0.004) −0.114 (<0.001) −0.469 (<0.001) −0.217 (<0.001) −0.065 (0.042) −0.074 (0.024) −0.115 (<0.001) 0.04 (0.219) 0.029 (0.370) 1.000 0.216 (<0.001)
−0.173 (<0.001) −0.163 (<0.001) −0.116 (<0.001) −0.178 (<0.001) −0.187 (<0.001) −0.013 (0.690) −0.02 (0.547) −0.181 (<0.001) −0.155 (<0.001) −0.005 (0.887) −0.059 (0.0770) −0.063 (0.059) 0.031 (0.349) −0.083 (0.012) 0.216 (<0.001) 1.000
Table 3 Associations of changes in weight, visceral adiposity, aerobic and muscle fitness, with changes in cardiovascular risk factors. Effect size is B coefficient (standard error) and standardized beta (ˇ), calculated by linear regression. Analyses were adjusted for baseline value of the independent variable, length of follow-up and smoking. Changes in 12-min running test and muscle fitness index were adjusted for changes in weight. Changes in weight and visceral fat were adjusted for change in 12-min running test and muscle fitness index. VFA = visceral fat area, Cooper test = 12-min running test, MFI = muscle fitness index. Variable
Weight B (SE)
VFA ˇ
Crude Systolic blood pressure (mmHg) 0.394 (0.077) 0.155 Diastolic blood pressure (mmHg) 0.388 (0.058) 0.203 Total serum cholesterol (mmol/L)* 0.379 (0.047) 0.251 LDL-cholesterol (mmol/L)* 0.417 (0.037) 0.339 HDL-cholesterol (mmol/L)* −0.081 (0.016) −0.165 Triglycerides (mmol/L)* 0.062 (0.046) 0.043 Adjusted Systolic blood pressure (mmHg) 0.722 (0.113) 0.275 Diastolic blood pressure (mmHg) 0.217 (0.083) 0.110 Total serum cholesterol (mmol/L)* 0.485 (0.067) 0.308 LDL-cholesterol (mmol/L)* 0.426 (0.053) 0.340 HDL-cholesterol (mmol/L)* −0.056 (0.023) −0.111 Triglycerides (mmol/L)* 0.202 (0.065) 0.139
P value B (SE)
Cooper test ˇ
P value B (SE)
MFI ˇ
P value B (SE)
ˇ
P value
<0.001 0.042 (0.012) 0.106 <0.001 0.074 (0.009) 0.248 <0.001 0.030 (0.008) 0.128 <0.001 0.046 (0.006) 0.236 <0.001 −0.001 (0.002) −0.152 0.174 −0.013 (0.007) −0.058
<0.001 <0.001 <0.001 <0.001 <0.001 0.073
−0.031 (0.016) −0.083 (0.012) −0.023 (0.010) −0.029 (0.001) 0.004 (0.003) 0.008 (0.009)
−0.065 0.042 −0.026 (0.187) −0.005 0.887 −0.217 <0.001 −0.676 (0.138) −0.155 <0.001 −0.074 0.024 −0.199 (0.112) −0.059 0.077 −0.115 <0.001 −0.174 (0.092) −0.063 0.059 0.040 0.219 0.034 (0.037) 0.031 0.349 0.029 0.370 −0.264 (0.105) −0.083 0.012
<0.001 0.070 (0.024) 0.172 0.009 0.045 (0.017) 0.144 <0.001 0.042 (0.015) 0.173 <0.001 0.038 (0.012) 0.192 0.013 −0.004 (0.005) −0.048 0.002 0.007 (0.001) 0.029
0.003 0.010 0.004 0.001 0.416 0.631
−0.012 (0.020) −0.041 (0.015) −0.013 (0.012) −0.004 (0.001) −0.002 (0.004) −0.012 (0.012)
−0.024 −0.109 −0.041 −0.017 −0.019 −0.042
0.546 0.005 0.294 0.660 0.639 0.302
−0.019 (0.212) −0.449 (0.156) −0.173 (0.126) −0.053 (0.101) −0.037 (0.042) −0.363 (0.123)
−0.003 −0.102 −0.051 −0.019 −0.033 −0.113
0.929 0.004 0.169 0.596 0.379 0.003
B coefficients (SE) are for change per one unit for weight, VFA and MFI; for 10 m change in the 12 min running test (Cooper test), * and for 0.1 mmol/L change in lipids.
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nificant. Statistical analysis was performed using SAS 9.1.3. for Windows (SAS Institute Inc. Gary NC). 3. Results 3.1. Total changes in exercise performance, body composition and CVD risk profile Anthropometric characteristics and cardiovascular risk profile of the cohort at baseline are shown in Table 1. At baseline the participants had a normal mean BMI (23.9 kg/m2 , range from 16.3 to 46.0 kg/m2 ). An improvement in both aerobic capacity and muscle performance was observed during the follow-up (Table 1). Mean aerobic performance in the 12-min running test at baseline was 2482 m (range 1000–3910) and improved by 170 m (SD 269) during the follow-up. Mean muscle fitness index at baseline was 8.0 points (range 1–15) and improved by 1.5 points (SD 2.3). During the follow-up, significant reductions were observed in weight (p = 0.008), fat mass, fat percentage, and VFA (p < 0.0001 for all) (Table 1). Systolic blood pressure decreased and HDL cholesterol increased significantly (p < 0.001 for both). In contrast, diastolic blood pressure, total and LDL cholesterol and triglycerides increased. 3.2. Association between weight loss, body composition and CVD status Weight loss strongly correlated with the reduction of BMI, waist circumference, FM, fat %, and VFA (Table 2). Weight loss significantly correlated with a decrease in both systolic and diastolic blood pressure (r = 0.203 and 0.155, respectively, p < 0.001), with a decrease in total and LDL cholesterol and triglycerides, and an increase in HDL cholesterol (p < 0.0001 for all). Decrease in VFA correlated with reductions in blood pressure and lipid levels similarly to those of weight loss (p < 0.001 for all), with the exception of triglycerides (NS). 3.3. Associations between the changes in exercise performance, body composition and CVD status Improvement in endurance and muscle performance significantly correlated with weight loss, decrease in waist circumference, and decreases in FM, fat % and VFA (p < 0.0001 for all) (Table 2). Correlations for the change in the 12-min running test were substantially higher than for the change in MFI. Decrease in blood pressure levels, particularly systolic blood pressure, correlated more strongly with the improvement in endurance performance than with muscle performance. Compared to the improvement in muscle performance, improvement in 12min running test correlated more strongly with improvement in lipid parameters. 3.4. Comparison of the effects of weight loss and exercise on CVD risk factors Associations between the changes in weight, endurance performance, blood pressure levels, and lipids were linear (data not shown), and therefore linear regression analysis was applied in the subsequent statistical analysis. Multiple linear regression analysis showed that the improvement in blood pressure and lipid levels with increased aerobic capacity was attributable to weight loss (Fig. 1). Additional adjustment for changes in either aerobic or muscle performance did not alter the effect of weight loss on CVD risk factors. The association of weight loss with changes in blood pressure and lipid levels
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remained significant after the adjustment for baseline weight, changes in both exercise parameters, length of follow-up and smoking (Table 3). The effects of the reduction in VFA on changes in blood pressure and lipid levels were smaller than that of weight loss (Table 3), but remained significant for blood pressure, LDL and total cholesterol levels after adjustment for confounding factors. Effects of the improvement in 12-min running test as a modifier of CVD risk factors were small, and were significant only for diastolic blood pressure after the adjustment for confounding factors. Increase in muscle performance was associated with the reduction of diastolic blood pressure and triglyceride levels, even after the adjustment for confounding factors.
4. Discussion In our prospective study of 1112 young Finnish men an intensive exercise program during military service significantly improved CVD risk profile. Particularly beneficial was aerobic exercise resulting in the reduction of visceral fat area. The beneficial changes in body composition and CVD risk factors were attributable to an exercise program without a dietary intervention. Therefore, this study provides population-level evidence for an independent contribution of exercise intervention to the improvement of CVD risk factors levels. Both endurance and muscle fitness performance improved during the 6–12 months exercise intervention, and both of them significantly reduced weight, central adiposity, total fat mass, and visceral fat area. Weight loss and beneficial body composition changes were greater in association with an improvement in endurance performance than with an improvement in muscle fitness performance. Similar body composition changes have previously been reported with moderate to vigorous exercise [15]. While the mean total weight loss in our cohort was modest, it was more pronounced in the overweight and obese young men (−3.2 kg for BMI of 25–29.9 kg/m2 , and −8.9 kg for BMI of ≥30 kg/m2 , respectively) [11]. The overall improvement in physical performance in our cohort was relatively modest, reflecting the heterogeneous physical activity background of study participants entering the military service. Similar studies from other military cohorts with similar methods are lacking, data are conflicting and thus direct comparison of the changes in physical performance is difficult. Physical activity is known to be protective against premature mortality and morbidity [16], but with most lifestyle intervention studies combining diet with weight loss and physical activity [17], the independent contribution of physical activity to improved health outcomes has remained unclear. In our study both weight loss and reduction in central adiposity, as well as improvement in physical performance were associated with a decrease in blood pressure levels and favourable changes in the lipid profile. The effect of improved exercise performance on the lowering of blood pressure and altering lipids was, however, attributable mainly to weight loss and reduction of VFA. This is most likely due to increased energy expenditure induced by exercise. Studies regarding changes in individual CVD risk factors in response to physical activity have been controversial. Exercise has not lowered blood pressure in some of the previous studies [18,19]. However, a meta-analysis by Whelton et al., reported that aerobic exercise lowered blood pressure levels both in hypertensive and normotensive individuals [20]. In our exercise-only intervention study of non-diabetic young men, we demonstrated that improvement in aerobic performance was associated with a reduction in abdominal obesity and blood pressure levels. Previous exercise intervention studies have observed an overall beneficial effect on the lipid profile, particularly with respect to
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HDL cholesterol and also triglycerides, but the effect has been variable and overall small across the studies. The dose and intensity of exercise required to achieve the desired changes in the lipid profile remain unclear [21]. Furthermore, it has also been unclear as to whether these effects are independent of the changes in body composition. In our study, we observed an increase in HDL and decrease in total and LDL cholesterol levels, which were attributable to weight loss and reduction of visceral fat mass. Our findings suggest that the effect of exercise on lipid profile is mediated by changes in weight and body composition. Central adiposity provides the key link between the improvement in exercise performance and reduction in CVD risk factors. Visceral fat has an independent curvilinear association with mortality [22]. Compared to total fat mass, high amounts of visceral fat have been associated more strongly with blood pressure, the HDL/total cholesterol ratio and insulin resistance [23]. Central adiposity has also been linked with elevated systolic blood pressure levels in the Nurses’ Health Study, and decreased visceral fat has been associated with a reduction in blood pressure [24]. Obesity and particularly visceral fat are associated with qualitative and quantitative changes in lipids and lipoproteins, such as increases in total cholesterol, very low-density lipoproteins (VLDL), small dense LDL particles, triglycerides and decreases in high-density lipoprotein (HDL) cholesterol levels [25]. Our study is in agreement with these findings showing that exercise intervention reduced VFA and resulted in favourable changes in lipid and lipoprotein levels. Diet is important for both weight loss and changes in cardiovascular risk factors, particularly lipid profile [26]. Our study was carried out in a military setting and did not include a dietary intervention. The intended content of energy in the food served to every conscript by the military forces is 3200–3600 kcal/day, of which 30–35% consist of fat [27]. Hence, the importance of exercise as a modifier of CVD risk factors is highlighted in this setting with no caloric restriction. Caloric restriction has been reported to have an independent effect and also a combined effect with exercise to improve CVD risk in healthy non-obese individuals [28]. Reports from the United States and Scandinavia have shown an increase in the prevalence of obesity among men entering military service [29,30], and a simultaneous gradual decline in aerobic fitness in the past decade [14]. In contrast, our results demonstrate weight loss, favourable changes in body composition and cardiovascular risk factor levels in association with improved exercise performance during the military service. Albeit these changes on average were modest, they were pronounced in overweight and obese men, and if maintained, these relatively small changes could potentially translate into substantial health benefits over time. The challenge, however, is the maintenance of the required levels of physical activity beyond the intervention period. This study has several strengths. It was a large intervention study to investigate the independent contribution of exercise on CVD risk factor levels among healthy young adults. The cohort was a representative sample of healthy Finnish male adults. Exercise performance was objectively measured both for endurance and muscle fitness. Moreover, the main meals and living circumstances were standardized for all participants. However, the study has limitations. We did not have a control group due to the study design. VFA was evaluated by InBody720 (BIA). More studies are needed to validate this method in different ethnic groups. Inevitable changes in diet and environment associated with military service may have had some effects on cardiovascular risk factors or body weight. Approximately 10% of the age group are exempt from military service during medical examination due to physical or mental reasons, and therefore it is likely that the most obese are not represented in our cohort. Our results are also limited to men, as the number of women entering military service in Finland is small and therefore women were excluded from statistical analysis.
In conclusion, our large study of young healthy men shows that high amounts of exercise, and particularly endurance training, were associated with reductions in blood pressure levels and favourable changes in the lipid profile during a 6–12-month follow-up period. The changes were attributable to weight loss and the reduction of abdominal fat area. Thus, exercise resulting in weight loss provides a successful tool to reduce the epidemic of obesity and to improve CVD risk factor levels among young men. Conflict of interest The authors have no conflict of interest relevant to the article. Acknowledgements The authors would like to thank Medical Colonel, M.D. Ph.D. Ari Peitso from the Finnish Defence Forces for his assistance with the study. Author Ilona Mikkola would like to thank the Finnish Cultural Foundation for its support to the study. References [1] Berenson GS, Srinivasan SR, Bao W, et al. Association between multiple cardiovascular risk factors and atherosclerosis in children and young adults. The Bogalusa Heart Study. N Engl J Med 1998;338:1650–6. [2] Olshansky SJ, Passaro DJ, Hershow RC, et al. A potential decline in life expectancy in the United States in the 21st century. N Engl J Med 2005;352:1138–45. [3] Hu FB, Willett WC, Li T, et al. Adiposity as compared with physical activity in predicting mortality among women. N Engl J Med 2004;351:2694– 703. [4] Tammelin T, Ekelund U, Remes J, et al. Physical activity and sedentary behaviors among Finnish youth. Med Sci Sports Exerc 2007;39:1067–74. [5] Healy GN, Wijndaele K, Dunstan DW, et al. Objectively measured sedentary time, physical activity, and metabolic risk: the Australian Diabetes, Obesity and Lifestyle Study (AusDiab). Diabetes Care 2008;31:369–71. [6] James PT, Rigby N, Leach R. The obesity epidemic, metabolic syndrome and future prevention strategies. Eur J Cardiovasc Prev Rehabil 2004;11:3–8. [7] Tuomilehto J, Lindstrom J, Eriksson JG, et al. Prevention of type 2 diabetes mellitus by changes in lifestyle among subjects with impaired glucose tolerance. N Engl J Med 2001;344:1343–50. [8] Blair SN, Church TS. The fitness, obesity, and health equation: is physical activity the common denominator? JAMA 2004;292:1232–4. [9] Oberman A. Healthy exercise. West J Med 1984;141:864–71. [10] Ko GT. Short-term effects after a 3-month aerobic or anaerobic exercise programme in Hong Kong Chinese. Diabetes Nutr Metab 2004;17:124–7. [11] Mikkola I, Jokelainen JJ, Timonen MJ, et al. Physical activity and body composition changes during military service. Med Sci Sports Exerc 2009;41:1735– 42. [12] Cooper KH. A means of assessing maximal oxygen intake. Correlation between field and treadmill testing. JAMA 1968;203:201–4. [13] Grant S, Corbett K, Amjad AM, et al. A comparison of methods of predicting maximum oxygen uptake. Br J Sports Med 1995;29:147–52. [14] Santtila M, Kyrolainen H, Vasankari T, et al. Physical fitness profiles in young Finnish men during the years 1975–2004. Med Sci Sports Exerc 2006;38:1990–4. [15] Slentz CA, Houmard JA, Kraus WE. Exercise, abdominal obesity, skeletal muscle, and metabolic risk: evidence for a dose response. Obesity (Silver Spring) 2009;17(Suppl. 3):S27–33. [16] Wei M, Kampert JB, Barlow CE, et al. Relationship between low cardiorespiratory fitness and mortality in normal-weight, overweight, and obese men. JAMA 1999;282:1547–53. [17] Yates T, Khunti K, Bull F, et al. The role of physical activity in the management of impaired glucose tolerance: a systematic review. Diabetologia 2007;50:1116–26. [18] Church TS, Earnest CP, Skinner JS, et al. Effects of different doses of physical activity on cardiorespiratory fitness among sedentary, overweight or obese postmenopausal women with elevated blood pressure: a randomized controlled trial. JAMA 2007;297:2081–91. [19] Ilanne-Parikka P, Laaksonen DE, Eriksson JG, et al. Leisure-time physical activity and the metabolic syndrome in the Finnish diabetes prevention study. Diabetes Care 2010;33:1610–7. [20] Whelton SP, Chin A, Xin X, et al. Effect of aerobic exercise on blood pressure: a meta-analysis of randomized, controlled trials. Ann Intern Med 2002;136:493–503. [21] Kraus WE, Slentz CA. Exercise training, lipid regulation, and insulin action: a tangled web of cause and effect. Obesity (Silver Spring) 2009;17(Suppl. 3):S21–6.
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