cardio - pulmonary fitness is related to the ability to perform large muscle , dynamic , moderate - to - high exercises for a prolonged period .
the performance of such exercises depends on the functional state of the cardiovascular , respiratory , and skeletal muscle systems .
a variety of tests have been used to check cardio - pulmonary fitness and some of these tests are quite popular , such as , the cooper 12-minute test .
the procedure of this test involves the participants running with maximal effort for 12 minutes exactly .
the advantages of cooper test are that the whole team can participate together , and compete against each other .
the test is relatively easy to carry out , and does not involve too much time or equipment .
it can also be used easily for training ; and , any improvements can be easily appreciated .
the disadvantages include that it is an indirect test , the results of which are not very accurate . also , it is suitable only for well trained individuals due to the fact it requires maximal effort for the entire length of the test .
another disadvantage is that the test does not give actual maximum oxygen consumption values ; it only gives a classification of poor to excellent .
hence , it has been suggested that this test is best for comparing athlete 's individual scores against each other to monitor improvements , rather than comparing the scores of the whole team . in the laboratory ,
maximum oxygen consumption is the gold standard in the assessment of cardio - pulmonary fitness .
normally , heart rate is controlled by autonomic nervous system activity . heart rate variability ( hrv )
hrv demonstrates a relationship between autonomic nervous system function ( sympathetic or vagal activity ) and cardiovascular system . on the other hand ,
hrv has been recognized as a predictor of cardiovascular events , both in symptomatic and asymptomatic population.[36 ] also , it was found that reduced hrv predicts hypertension and hyperglycemia in the future .
the simplest variable is the standard deviation of normal - to - normal qrs intervals ( sdnn ) in a continuous electrogram ( ecg ) recording .
traditionally , hrv is recorded over a longer period ( 24 hour ) ; however , some investigators have reported that ultra - short hrv ( 2 - 15 minutes ) is strongly correlated with the 24-hour hrv .
the aim of this study was to assess the cardio - pulmonary fitness by ultra - short hrv .
study population was divided into 3 groups : group-1 ( n = 40 ) consisted of military sports man who volunteered to participate in this study . group-2 ( n = 40 ) were healthy age - matched sedentary male subjects who had a normal bmi [ bmi = 19 - 25 kg / m ) .
group-3 ( n = 40 ) consisted of healthy age - matched obese male subjects [ bmi > 29
the subjects of the research were all free of cardiovascular and pulmonary disease , alcohol use , and diabetes mellitus ; and , were not taking any kind of medication , and did not present with any abnormal electrocardiographic patterns .
, all the subjects rested in a supine position for a minimum of 15 minutes in a room with a constant temperature of 25 degree c. for the holter recording , standard digital devices were used .
after holter recording , bruce protocol treadmill test was used . at timed stages during the run , the slope of the treadmill is increased as detailed in table 1 .
maximum oxygen consumption ( vo2max ) , which has been shown to be an objective criterion of cardiopulmonary fitness , was calculated by foster equation : bruce protocol treadmill test vo2max ( ml / kg / min ) = 14.8  [ 1.379  t ] + [ 0.451  t ]  [ 0.012  t ] 
t is the total time of the test expressed in minutes and fractions of a minute .
comparisons between groups were made using student 's t - test and mann - whitney u test as appropriate .
study population was divided into 3 groups : group-1 ( n = 40 ) consisted of military sports man who volunteered to participate in this study . group-2 ( n = 40 ) were healthy age - matched sedentary male subjects who had a normal bmi [ bmi = 19 - 25 kg / m ) .
group-3 ( n = 40 ) consisted of healthy age - matched obese male subjects [ bmi > 29
the subjects of the research were all free of cardiovascular and pulmonary disease , alcohol use , and diabetes mellitus ; and , were not taking any kind of medication , and did not present with any abnormal electrocardiographic patterns .
before the test , all the subjects rested in a supine position for a minimum of 15 minutes in a room with a constant temperature of 25 degree c. for the holter recording , standard digital devices were used .
after holter recording , bruce protocol treadmill test was used . at timed stages during the run , the slope of the treadmill is increased as detailed in table 1 .
maximum oxygen consumption ( vo2max ) , which has been shown to be an objective criterion of cardiopulmonary fitness , was calculated by foster equation : bruce protocol treadmill test vo2max ( ml / kg / min ) = 14.8  [ 1.379  t ] + [ 0.451  t ]  [ 0.012  t ] 
t is the total time of the test expressed in minutes and fractions of a minute .
comparisons between groups were made using student 's t - test and mann - whitney u test as appropriate .
the mean age was identical between 3 groups as might be expected from the matching .
baseline characteristics of the 3 groups involved in the study relationship between sdnn and estimated vo2 max are demonstrated in table 3 .
relation between standard deviation of normal - to - normal qrs intervals ( sdnn ) and maximum oxygen consumption ( vo2max ) of the three groups involved in the study when the study population was divided into quartiles of sdnn ( first quartile : < 60 msec ; second quartile : > 60 and < 100 msec ; third quartile : > 100 and < 140 msec ; and fourth quartile : > 140 msec ) , progressive increase was found in vo2max ; and , sdnn was significantly linked with estimated vo2max values [ figure 1 ] . maximum oxygen consumption ( vo2max ) of study population compared by quartiles of standard deviation of normal - to - normal qrs intervals ( sdnn ) . when the study population was divided into quartiles of sdnn ( first quartile : < 60 msec ; second quartile : > 60 and < 100 msec ; third quartile : > 100 and < 140 msec ; and fourth quartile : > 140 msec ) , progressive increase was found in vo2max .
the mean age was identical between 3 groups as might be expected from the matching .
relation between standard deviation of normal - to - normal qrs intervals ( sdnn ) and maximum oxygen consumption ( vo2max ) of the three groups involved in the study when the study population was divided into quartiles of sdnn ( first quartile : < 60 msec ; second quartile : > 60 and < 100 msec ; third quartile : > 100 and < 140 msec ; and fourth quartile : > 140 msec ) , progressive increase was found in vo2max ; and , sdnn was significantly linked with estimated vo2max values [ figure 1 ] . maximum oxygen consumption ( vo2max ) of study population compared by quartiles of standard deviation of normal - to - normal qrs intervals ( sdnn ) . when the study population was divided into quartiles of sdnn ( first quartile : < 60 msec ; second quartile : > 60 and < 100 msec ; third quartile : > 100 and < 140 msec ; and fourth quartile : > 140 msec ) , progressive increase was found in vo2max .
previously , 24 hour was determined as an optimal cut point for hrv recording and analysis .
bigger et al . found that measures of rr variability calculated from short ( 2 to 15 minutes ) ecg recordings are remarkably similar to those calculated over 24 hours .
hrv has been recognized as a predictor of cardiovascular events both in symptomatic and asymptomatic population.[36 ] it was also used in risk stratification for sudden cardiac death and diabetic autonomic neuropathy .
they used hrv as a tool for noninvasive testing of autonomic nervous system activity with exercise training .
they showed that regular exercises result in a significant improvement of all hrv indices . in the present study ,
we have analyzed cardio - pulmonary fitness ( vo2max ) and ultra - short hrv ( sdnn ) .
we showed that sdnn is a simple cardio - pulmonary fitness test which just requires 15 minutes , and involves no exercise such as in the treadmill or cycle test .
previously , 24 hour was determined as an optimal cut point for hrv recording and analysis .
bigger et al . found that measures of rr variability calculated from short ( 2 to 15 minutes ) ecg recordings are remarkably similar to those calculated over 24 hours .
hrv has been recognized as a predictor of cardiovascular events both in symptomatic and asymptomatic population.[36 ] it was also used in risk stratification for sudden cardiac death and diabetic autonomic neuropathy .
they used hrv as a tool for noninvasive testing of autonomic nervous system activity with exercise training .
they showed that regular exercises result in a significant improvement of all hrv indices . in the present study , we have analyzed cardio - pulmonary fitness ( vo2max ) and ultra - short hrv ( sdnn ) .
we showed that sdnn is a simple cardio - pulmonary fitness test which just requires 15 minutes , and involves no exercise such as in the treadmill or cycle test .
in conclusion , the results of this study demonstrate that exercise training improves cardio - respiratory autonomic function ( and increase heart rate variability ) .
improvement in cardio - respiratory autonomic function seems to translate into a lower rate of long term mortality .
ultra - short hrv is a simple cardio - pulmonary fitness test which just requires 15 minutes , and involves no exercise such as in the treadmill or cycle test .
 objectives : it is known that exercise induces cardio - respiratory autonomic modulation . 
 the aim of this study was to assess the cardio - pulmonary fitness by ultra - short heart rate variability.materials and methods : study population was divided into 3 groups : group-1 ( n = 40 ) consisted of military sports man . 
 group-2 ( n = 40 ) were healthy age - matched sedentary male subjects with normal body mass index [ bmi = 19 - 25 kg / m2 ) . 
 group-3 ( n = 40 ) were healthy age - matched obese male subjects [ bmi > 29 kg / m2 ) . 
 standard deviation of normal - to - normal qrs intervals ( sdnn ) was recorded over 15 minutes . 
 bruce protocol treadmill test was used ; and , maximum oxygen consumption ( vo2max ) was calculated.results:when the study population was divided into quartiles of sdnn ( first quartile : < 60 msec ; second quartile : > 60 and < 100 msec ; third quartile : > 100 and < 140 msec ; and fourth quartile : > 140 msec ) , progressive increase was found in vo2max ; and , sdnn was significantly linked with estimated vo2max.conclusion:in conclusion , the results of this study demonstrate that exercise training improves cardio - respiratory autonomic function ( and increases heart rate variability ) . 
 improvement in cardio - respiratory autonomic function seems to translate into a lower rate of long term mortality . 
 ultra - short heart rate variability is a simple cardio - pulmonary fitness test which just requires 15 minutes , and involves no exercise such as in the treadmill or cycle test . 
INTRODUCTION
MATERIALS AND METHODS
Study population
Ultra-short heart rate variability recording and analysis
Cardio-pulmonary fitness test
Statistical analysis
RESULTS
Baseline characteristics
Relation between standard deviation of normal-to-normal QRS intervals (SDNN) and maximum oxygen consumption (VO
DISCUSSION
Heart rate variability versus ultra-short heart rate variability recording
Ultra-short heart rate variability as a novel tool for cardio-pulmonary fitness test
CONCLUSION