Download The aerobic capacity and fitness of Hungarian soldiers

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.
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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).
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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.
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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
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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
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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
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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
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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.
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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
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