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MEDICINE AARMS Vol. 6, No. 4 (2007) 687–697 The aerobic capacity and fitness of Hungarian soldiers LÁSZLÓ KOHUT National Healthcare Center, Cardiological Rehabilitation Institute, 1st Cardiological Rehabilitation Unit, Balatonfüred, Hungary Regular exercise plays an important role in health maintenance. Physical activity decreases the emergence and progression of hypertension, ischemic heart disease, diabetes, stroke, some tumors, osteoporosis and depression. According to exercise physiology studies, regular exercise at the anaerobic threshold increases performance and improves aerobic output. Aerobic capacity reflects the endurance, fitness and aerobic metabolic activity in the body, which is determined by the cardiac output, the adaptation of the respiratory system and the oxygen utilization of the skeletal muscle. The goal of this study was to compare the respiratory and metabolic parameters of young, healthy soldiers that regularly participate in dynamic or resistance type physical activity to those living a sedentary lifestyle. 38 healthy soldiers (average age: 26.4 years) were included in the study. Spiroergometric studies were performed according to Bruce protocol and the results were statistically analyzed (duration of exercise, performance, minute ventilation (VE), oxygen uptake (VO2), carbon dioxide output (VCO2), metabolic equivalent (MET), respiratory quotient (RQ), maximal oxygen uptake (VO2max), VO2/kg, VCO2/kg, anaerobic threshold (AT), heart rate (HR), blood pressure (RR)). It has been found that during strenuous exercise the parameters pertaining to the aerobic capacity (performance, VE, VO2, VCO2, VO2max, VO2/kg, VCO2/kg, HR) draw nearer to each other in soldiers used to regular exercise, while in sedentary soldiers there is still a large difference at the end of the exercise. In conclusion, the aerobic capacity and performance was higher in those soldiers that were used to regular dynamic or resistance type activity, compared to those age- and assignment-matched subjects that did not participate in regular exercise. Received: October 1, 2007 Address for correspondence: LÁSZLÓ KOHUT National Healthcare Center Cardiological Rehabilitation Institute 1st Cardiological Rehabilitation Unit Balatonfüred, Hungary E-mail: [email protected] L. KOHUT: The aerobic capacity and fitness of Hungarian soldiers Introduction The army is typically the type of organization, where a certain level of fitness is necessary for doing routine daily tasks. Greater and greater level of participation in international missions especially increased the importance of the physical fitness of the soldiers. Today it is expected of soldiers to do their assignment continuously, for hours at a time. Several international studies have shown that good physical condition also has an important role in health maintenance. Regular physical activity decreases the occurrence of hypertension, coronary artery disease, diabetes mellitus, stroke, osteoporosis and depression.1,2 In a 27-year-long prospective study, a multi-level physical activity score was established that could quantify young adults. Low level cardio-respiratory function is a strong and independent marker of cardiovascular disease and total mortality.3 According to one estimation of the WHO, in the background of early mortality 40% is lifestyle, 25% genetics, 25% environmental pollutants. The remaining 10% could be avoided by the improvement of healthcare worldwide. Accurate measurement of fitness in a population could play an important role in determining their health status and prognosticating later risks to their health.4 Both the active professional and contract soldiers of the army have to participate in regular testing of their physical fitness. It is expected that they should be fit. Moreover, some members of the armed forces train at a high level, regularly and semiprofessionally. One practical and sensitive method of measuring their fitness and endurance is the spiroergometric measurement.5 Measuring gas exchange during stepwise increasing exercise load (during which, in case of proper oxygen supply, skeletal muscle makes energy with the help of the Krebs cycle and terminal oxidation) there is a possibility of measuring personal performance, their aerobic capacity, acidbase status and monitoring the process of restitution.6,7 The maximal oxygen uptake (VO2 max) is a basic measure of stress physiology, a measuring unit of cardiovascular and anaerobic capacity. Howley et al. have developed the definition of VO2 max. in their earlier works, where they measured the gas exchange parameters in 3 minute intervals of men running at different speeds.8,9 The aim of our study is to measure aerobic capacity and endurance with the help of spiroergometry in soldiers that train regularly, compared to those living a sedentary lifestyle. 688 AARMS 6(4) (2007) L. KOHUT: The aerobic capacity and fitness of Hungarian soldiers Methods 38 healthy soldiers (all men) participated in the study. Their average age was 26.4 years (range 21–32). The soldiers have been sorted into two groups of 19 each, based on their level of physical and sporting activity (bicycling and/or jogging and/or wrestling). The soldiers that exercised regularly, have done so at least 3 times a week minimum 3 hours each time. A spiroergometric study has been done according to Bruce protocol on each man after acquainting them with the machine, a Shiller spiroergometer. The gotten results have been analyzed.10 The stress test was continued to the target heart rate or until symptoms of fatigue appeared. The exercise was started at 2.7 km/h at an incline of 10% for 3 minutes, then the velocity (4.0–5.4–6.7–8.0 km/h), and incline (12–14–16–18%) was increased until the target heart rate was reached or until symptoms of fatigue appeared.11 Oxygen consumption, carbon dioxide production, ventilation and heart rate was measured with each breath on a SCHILLER CS 200 Ergo-Spirometry (Ganshorn Medizin Electronic, Baar, Switzerland) metabolic unit. During the measurement the gas exchange parameters, the time of exercise, performance, minute ventilation (VE), oxygen consumption (VO2), carbon dioxide production (VCO2), metabolic equivalent (MET), respiratory quotient (RQ), maximal oxygen consumption (VO2 max), aerobic threshold (AT), heart rate (HR) and blood pressure (RR) were determined.12–14 Gas exchange data The gas exchange was measured by standardized methods. VO2 max was determined at the plateau of the VO2 curve (delta VO2 60 ml/min at VO2 max), at this point the maximal air exchange rate was larger than 1.1.15,16 There are no generally accepted criteria for measuring VO2 max, therefore we have used the data coming from our laboratory, measured on 150 subjects of different age, gender and level of training. Age-specific maximal heart rate as a secondary criterion at determining VO2 max has been used.17 Demographic data 38 healthy soldiers (all men) participated in the study. Their demographic data are the following: average age 26.4±5.3 yrs, average height 176.8±4.1 cm, average body surface area 1.83±3.2 m2, average mass 76.9±4.2 kg, average BMI 25.16±1.7. The regularly exercising soldiers trained 3–5 times a week (3–6 hours each time), the sedentary soldiers trained 1–2 times a week (1–2 hours each time) (Table 1). AARMS 6(4) (2007) 689 L. KOHUT: The aerobic capacity and fitness of Hungarian soldiers Table 1. Demographic data of the subjects Regularly excercising soldiers 19 25.8±4.7 1.86±0.2 177±5.2 76.7±3.7 24.9±1.7 3–5 6.4±3.4 Dynamic/static 11 (57%) 121±14.5 71±6.3 Men Age (years) Body surface area (m2) Hight (cm) Weight (kg) BMI (kg/m2) Training/week Total time of training (hours) Type of exercise Smoking Systolic blood pressure (Hgmm) Diastolic blood pressure (Hgmm) Sedentary soldiers 19 27.2±5.3 1.79±0.1 175±4.3 77.2±5.1 25.2±1.8 1–2 1.9±1.1 Dynamic/static 15 (79%) 122±12.7 75±9.4 Inclusion criteria: Healthy professional or contract soldiers; Not on medication; Normotensive; Normal lab parameters; Number of times per week doing exercise: Regularly, 3–5 times per week; Irregularly, 1–2 times per week; Negative stress test done within a year. Exclusion criteria: Non-compliance; Abnormal lab results; Exercising less than once a week; BMI>27. Statistical analysis All data are presented as the average ± standard deviation, and were analyzed by the Student two sample t-test. The p<0.05 was considered significant. Results All 38 subjects reached or surpassed the goal exercise level (target HR 94–100%). The duration of the exercise ranged between 14 and 25 minutes. VO2 max changed between 38.02±9.37 ml/kg/min. The minute ventilation (VE) increased from its baseline level of 13.5±1.1 l/min to 78±6 l/min. These values are presented in Table 2. 690 AARMS 6(4) (2007) L. KOHUT: The aerobic capacity and fitness of Hungarian soldiers Table 2. Results of the exercise testing Duration of exercise (min) Performance (MET) Power (Watt) VE l/min VO2 l/min VCO2 l/min RQ VO2 ml/kg/min VCO2 ml/kg/min Heart rate (HR) Regularly exercising N=19 21.50±4.1 18.2 405±24 85.14±13.9 3.092±0.43 3.401±0.42 1.31±0.16 41.74±2.18 44.52±3.53 174±11 Not exercising regularly N=19 19.04±5.3 17.1 340±35 72.58±24.7 2.967±0.54 3.264±0.87 1.20±0.23 35.35±2.88 39.74±5.61 185±19 p value p=NS p=0.005 p=0.043 p=NS p=0.043 p=0.07 p=NS p=0.017 p=0.023 p=NS These data show as a percentage that these percentages get closer to each other at maximal load, while for those not in training they still had significant differences at the end of the exercise (Table 3). Table 3. Data in percentages. Power (Watt) VE l/min VO2 l/min VCO2 l/min VO2 ml/kg/min VCO2 ml/kg/min Heart rate (HR) Regularly exercising N=19 149±13 70±9.4 109±11.4 115±12.6 109±11.4 115±12.6 91±4 Not exercising regularly N=19 134±25 64±15.3 101±15.7 110±17.2 101±15.7 110±17.2 93±8 p value p=0.005 P=0.004 p=0.007 p=0.003 p=0.006 p=0.004 p=0.005 The maximum load reached was significantly higher among regularly exercising soldiers as compared to their sedentary comrades (149±13 Watt versus 134±25 Watt p=0.005). However, there was no significant difference in the duration of the exercise (21.50±4.1 min versus 19.04±5.3 min, p=NS). The regularly exercising soldiers did not just fare better as a group as compared to their sedentary comrades, but even their data points were consequently closer to each other, while for the other group the SD was significantly higher (Figure 1). The change in the ratio of carbon dioxide production to oxygen consumption (respiratory quotient RQ) did not show significant differences between the regularly exercising and sedentary soldiers (1.31±0.16 versus 1.20±0.23, p=NS). This number changed on average from the baseline 0.75±0.04 to 1.26±054. The increase of RQ to above 1 means also the prioritizing of the anaerobic metabolism, since the growing AARMS 6(4) (2007) 691 L. KOHUT: The aerobic capacity and fitness of Hungarian soldiers amount of lactic acid releases more and more carbon dioxide from the blood bicarbonate pool, which in turn increases the amount of carbon dioxide in the exhaled air (Figure 2). Figure 1. The change in power as a function of time. Figure 2. The change of RQ as a function of exercise time. The maximal oxygen uptake is by definition the largest amount of oxygen taken up by the body, whose amount cannot be increased by increasing the workload. VO2 max is calculated by multiplying the minute volume with the arterio-venous difference. Not surprisingly, the maximal oxygen uptake was higher in case of regularly exercising 692 AARMS 6(4) (2007) L. KOHUT: The aerobic capacity and fitness of Hungarian soldiers soldiers when compared with their sedentary comrades (3.092±0.43 l/min versus 2.967±054 l/min, respectively, p=0.043) (Figure 3). Figure 3. The change of maximal oxygen uptake during exercise. Figure 4. The relationship among the heart rate, oxygen consumption and pulse rate. In summary, the physiological cardiovascular and pulmonary response to increasing exercise load is an increase in blood pressure, heart rate and minute ventilation. Oxygen AARMS 6(4) (2007) 693 L. KOHUT: The aerobic capacity and fitness of Hungarian soldiers consumption increases parallel with the exercise load, since minute volume and tissue oxygen extraction equally increases.18 During early exercise the increase in minute volume is combination of the increase in pump volume and heart rate, but in later stages the increase of minute volume comes mostly from a further increase in heart rate. The regularly exercising soldiers showed significantly better cardio-respiratory adaptation as compared to their sedentary counterparts. The oxygen consumption was higher at lower heart rates, which means better usage of the aerobic capacity, and thus providing greater energy source (Figure 4). Discussion The training of soldiers and keeping up their level of fitness costs a lot of money and energy, moreover it also requires a high level of competency. One has to do their utmost to ensure the flawless execution of these goals. Human resources are especially important in this system. Measuring the psychological and physical stress endurance of soldiers on operative duty is highly important in a world in which requirements are changing rapidly. The personnel of the army have to comply with orders even in extreme climactic conditions and in all kinds of fighting situations. Measuring their fitness is singularly important for them to do their duty. It is also important to discover special talents and prognosticate maximum exercise tolerance in choosing people for the force. It has been proven the validity of using stress testing by BRUCE protocol, using 38 young, healthy soldiers in determining their cardio-respiratory fitness.19 This study shows the adaptability of the body in increasing amounts of exercise from baseline to maximal exercise. The components of this adaptation are the pulmonary gas exchange, the pump function of the heart, the peripheral adaptation of circulation and the oxygen uptake of the skeletal muscle. There was a significant difference between the two (regularly exercising and sedentary) study groups in work load, maximum power, amount of exercise, oxygen consumption and in carbon dioxide production. A significant difference in the time of exercise, in the respiratory quotient and in the reached maximal pulse rate has not been found. The kinetics of the changes in the cardiovascular and respiratory systems shows the state and fitness of the body. The rise in the heart rate even at lower exercise levels predicts the fitness of the subject (HR max 174±11 l/min versus 185±19 l/min, respectively, p=NS). The regularly exercising soldiers showed significantly better cardio-respiratory adaptation compared to the sedentary control group. The spiroergometric data measured during exercise show very sensitive parameters for 694 AARMS 6(4) (2007) L. KOHUT: The aerobic capacity and fitness of Hungarian soldiers prognosticating the aerobic capacity, for example, the minute ventilation was higher (85.14±13.9 l/min) in regularly exercising soldiers versus their sedentary controls (72.58±24.7 l/min), but this difference was not clinically significant (p=NS). Oxygen consumption was significantly higher in the trained group (3.401±0.42 l/min versus 3.264±0.87 l/min, p=0.07, and 41.74±2.18 ml/kg/min versus 35.35±2.88 ml/kg/min, p=0.017). The carbon dioxide production also showed significant differences between the two groups (44.52±3.53 ml/kg/min versus 39.74±5.61 ml/kg/min, p=0.023). The compared results in percentages showed convergence among regularly exercising soldiers. There was a very little SD in this group, and thus their curves run almost on each other. These results showed a larger SD in the sedentary group, thus the curves diverged at higher aerobic capacities. Williams et al. found that regular training programs among soldiers improved the maximal oxygen uptake.20 Kraemer et al. compared resistance-type and dynamic-type training among soldiers, and found that in those that did dynamic exercises became more physically fit.21 Pang N Shek et al. studied the effect of basic training on soldiers’ lifestyles, and he found that this significantly improves their health and decreases their morbidity.5 Our own study also showed that aerobic fitness is higher in those subjects who train regularly, since when regularly moving large muscle groups, it increases their fitness and health.22,23 Our study conclusively showed that regularly exercising soldiers are able to improve their oxygen consumption compared to those that are sedentary. This is the result of improved gas exchange. Knapik et al. also proved that a new training program based on dynamic exercises showed significantly better results than the traditional basic physical training.24 Kang et al. detected significantly shorter restitution time and better gas exchange parameters in those subjects who had larger aerobic capacity.25 We have continued the testing in our study to maximal or close to maximal pulse rate, and during this we measured the maximal oxygen consumption of the subject. Hurley et al. did similar studies, in which they concluded that the intensity and time of the exercise determines the rate of adjustment.4 This results from the fact that those subjects who do sports regularly, stress their body’s homeostatic mechanisms more than those that are sedentary.26 These findings were confirmed in our studies. Aerobic fitness also improves gas exchange parameters. Olds and Abernethy have also proven this fact when they compared subjects doing aerobic sports at medium and high intensities.27 Therefore, in practice aerobic fitness is crucial for soldiers, thus they should be encouraged to do fitness plans that include more aerobic type activity, this way increasing their level of fitness and readiness. AARMS 6(4) (2007) 695 L. KOHUT: The aerobic capacity and fitness of Hungarian soldiers Conclusions The results of our study show the following: Analyzing performance results in accurate prediction of the fitness of a soldier. Soldiers that trained on a regular basis had significantly better cardio-respiratory adaptation as compared to those who are sedentary. Spiroergometric parameters measurable during the stress test have accurate predictive value to judge aerobic capacity. At maximal training level those soldiers that train regularly had their percentage values approximate each other with a much smaller SD, thus they can practically be considered equal, but these values of the sedentary soldiers there remained a large difference in their aerobic capacity. With the use of spiroergometrics we can greatly help to use military human resources more effectively and safely. It is important for success for soldiers on a military mission to reach approximately similar level of fitness. List of abbreviations: AT – anaerobic (respiratory) threshold BMI – body mass index HR – heart rate MET – metabolic equivalent RQ – respiratory quotient RR – blood pressure VCO2 – carbon dioxide output VE – minute ventilation VO2 – oxygen uptake VO2 max – maximal oxygen uptake References 1. BUCHFUHRER, M.J., HANSEN, J.E., ROBINSON, T.E., SUE, D.Y., WASSERMAN, K., WHIPP, B.J.: Optimizing the exercise protocol for cardiopulmonary assessment. J. Appl. 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HAURET et al.: Evaluation of a standardized physical training program for basic combat training. J. Strength Cond. Res., 19(2) (2005) 246. 25. JIE KANG, HOFFMAN, J.R., JOOHEE, I.M., SPIERING, B.A. et al.: Evaluation of physiological responses during recovery following three resistance exercise programs. J. Strength Cond. Res., 19(2) (2005) 305. 26. WILMORE, J.H., ROBY, F.B., STANFORTH, P.R. et al.: Ratings of perceived exertion, heart rate, and treadmill speed in the prediction of maximal oxygen uptake during submaximal treadmill exercise. J. Cardiopulm. Rehab., 5 (1985) 540–546. 27. OLDS, T.S., ABERNETHY, P.J.: Postexercise oxygen consumption following heavy and light resistance exercise. J. Strength Cond. Res., 7 (1993) 147–152. AARMS 6(4) (2007) 697