physical fitness directly affects one s health state and becomes the basis of healthy 
 adulthood1 .
therefore , suitable physical 
 activity in children and adolescents contributes to the development of their physique , 
 strength , and balance .
many developed countries have national projects designed to encourage 
 students to enhance their physical fitness , e.g. , fitnessgram in the united states , trimming 
 130 in germany , participaction in canada , eurofit in europe .
health - related physical fitness 
 measures were first developed in 2009 in korea to evaluate students physical strengths 
 ( cardiorespiratory endurance , muscular strength , muscular endurance , flexibility , and body 
 fat ) .
the physical activity promotion system ( paps ) is used for continuous management of the 
 degrees of improvement in physical fitness and activities among elementary , middle , and high 
 school students through systematic evaluation of their physical fitness as well as the 
 recommendation of desirable physical activities to the students via their parents and 
 teachers .
a cardiorespiratory endurance test includes stepping , running , and walking , and 
 its evaluation results are classified into five grades using the heart rate to evaluate 
 heart function2 .
the current study focuses 
 only on the measured physical fitness levels and lacks follow - up management .
efficient 
 management by exercise programs that provide various benefits should be offered to 
 elementary school children . in the recent years
, studies have been conducted on exercise 
 machines , such as the simulator , that are used to enhance the muscle strength and 
 cardiorespiratory endurance , improve flexibility , and reduce body fat3 , 4 .
the ski simulator exercises in particular are designed to 
 mimic snow surface repulsion ; hence , they have the advantage of providing resistance .
such 
 resistance exercises enhance the muscle mass and stimulate muscle strengthening , thus 
 efficiently aligning the body parts and maintaining good posture .
they also improve one s 
 ability to perform various exercises requiring muscle strength , endurance , and energy ; thus , 
 they can positively influence basic health functions such as metabolism and cardiovascular 
 functioning6 , 7 . in a study on the effects of simulator - based exercises on injury 
 prevention ,
lee et al.8 reported that 
 training with a ski simulator contributes to increased range of motion and improved 
 hamstring strength , which help to prevent sports - related injuries .
however most previous 
 studies analyzed the skier s posture9 , 10 , and some differences were noted between 
 individuals depending on the exercise intensity and the simulator type . due to continuous 
 demand for research in this area , in this study , the heart rate was measured and analyzed 
 after a ski simulator exercise and the harvard step test .
these exercises have various 
 effects that can be used to evaluate the cardiopulmonary endurance by calculating the 
 post - exercise recovery rate . the body mass index ( bmi )
analysis can provide useful 
 information . because simulator exercises improve the muscle strength and endurance , this 
 study aimed to assess the exercise performance capacity improvements of elementary school 
 students .
participants included 77 elementary school students ( normal weight , 40 students ; overweight 
 and obesity , 37 , based on the asia oceania association for the study of obesity standards ) 
 with no previous or current foot injury .
this study was approved by the ethics committee of 
 the institutional review board of pukyong national university .
the cohort size was 
 calculated using the g*power 3.1 version program by faul et al11 .
the specifications of the sample calculated by this 
 analysis was 70 participants with a 0.05 significance level , 0.95 power , and 0.8 effect size 
 being the largest size ; therefore , this cohort ( 77 participants ) satisfied the required 
 sample size criteria ( table 1table 1.participants characteristicsnormal ( 40)over weight / obesity ( 37)height ( cm)149.28.1151.97.2weight ( kg)45.16.455.86.3bmi ( kg / m)20.21.624.11.0normal group ( 18.5  bmi < 23.0  kg / m ) , overweight , obesity ( bmi  
 23.0  kg / m )  aoaso ( asia oceania association for the study of obesity ) s 
 standards ) .
this study was conducted after obtaining written informed consent of the 
 participants and their parents and teachers .
the ski simulators ( pro ski simulator ; slovenia ) were fixed onto a flat 
 surface consisting of a platform on wheels that moved left and right on two bowed parallel 
 metal rails .
rubber belts fastened the platform to the rails and ensured that it regained 
 its resting position in the middle of the apparatus .
the ski simulator s band elasticity had 
 a rotation radius of 16 levels ; larger the rotation radius , weaker was the band elasticity . 

this study conducted the experiment with two elasticity strength levels . to ensure accuracy , 
 sufficient time
was given to each subject for practice , and then the actual skiing was 
 performed for 3 minutes .
each subject held a strap in each hand to maintain balance , and a 
 low intensity ski simulator setting was used for the study .
each participant performed the 
 harvard step movements for 3 minutes and then rested in a chair for 3 minutes .
the height of 
 the step box for harvard step test was 20.3  cm , and the steps were performed at a rate of 24 
 steps per minute . to ensure postural accuracy , each subject
a heart rate monitor and a stopwatch were used in this study , and 
 cardiorespiratory endurance was calculated by the physical efficiency index ( pei ) formula 
 described below.pei = d/(2  p )  100d : duration 
 of the exercise ( s)p : first phase ( 6090 s ) + second phase 
 ( 120150 s ) + third phase ( 180210 s ) heart rates normal group ( 18.5  bmi < 23.0  kg / m ) , overweight , obesity ( bmi  
 23.0  kg / m )  aoaso ( asia oceania association for the study of obesity ) s 
 standards using these methods , the heart rate in each phase as well as the differences in the 2 
 groups and the 2 exercises were computed through analysis of the biomechanical factors .
each 
 subject rested for 10 minutes between the conditions , which were performed in a random order 
 to avoid compromising the results .
the data were statistically processed using the 
 statistical package for the social sciences , version 23.0 .
the independent t - test and paired 
 t - test were used to examine the differences , which were considered statistically significant 
 at p values < 0.05 .
using the aforementioned methods , the movement - dependent cardiorespiratory endurance 
 factors of heart rate and pei were calculated .
there was a significant difference among the 
 bmi based groups at 2 and 3 minutes when participants were exercising and at 6 minutes when 
 they had cooled down .
furthermore , the normal weight group had higher pei levels ( table 2table 2.heart rate and physical efficiency index ( pei)ski simulatornormaloverweight / obesity1 minute84.321.481.813.72 minute122.110.1139.612.7***3 minute130.17.4150.010.5***4 minute84.711.787.411.55 minute81.111.184.411.16 minute80.611.887.513.0*pei61.45.656.33.5***harvard stepnormaloverweight / obesity1 minute92.819.793.615.52 minute129.612.6140.414.8**3 minute137.89.3147.914.9**4 minute87.116.685.818.65 minute83.819.083.517.46 minute85.112.486.514.2pei57.55.555.24.2*normalski simulatorharvard step1 minute84.321.492.819.7 * 2 minute122.110.1129.612.6**3 minute130.17.4137.89.3***4 minute84.711.787.116.65 minute81.111.183.819.06 minute80.612.485.112.4pei 61.45.657.55.5**overweight / obesityski simulatorharvard step1 minute81.813.793.615.5**2 minute139.612.7140.414.83 minute150.010.5147.914.94 minute87.411.585.818.65 minute84.411.183.517.46 minute87.513.086.514.2pei56.33.555.24.2*<0.05 , * * < 0.01 , * * * < 0.001 .
pei = d/(2  p )  100 ; d : duration of the exercise ( s ) ; p : first phase ( 6090  s ) + second phase ( 120150  s ) + third phase ( 180210  s ) heart 
 rates ) .
the t - test results regarding the participants heart rate before and after 
 the exercises showed that the average heart rate of the normal weight group was higher 
 during step - boxing ; however , the overall pei was higher during skiing .
the obesity group 
 revealed significant differences in the initial stages of the exercise , and the overall pei 
 of the obese group was higher during skiing . * < 0.05 , * * < 0.01 , * * * < 0.001 .
pei = d/(2  p )  100 ; d : duration of the exercise ( s ) ; p : first phase ( 6090  s ) + second phase ( 120150  s ) + third phase ( 180210  s ) heart 
 rates
the american college of sports medicine has underscored the importance of physical strength 
 with regard to health over physical strength in terms of motor skills based on the fact that 
 a decline in the capacities of body composition , cardiorespiratory endurance , muscular 
 strength , and muscular endurance and flexibility significantly increases the probability of 
 lifestyle diseases and health impairments .
relying on the kinetic functions of the heart and 
 lungs , cardiorespiratory endurance refers to the body s ability to continue supplying energy 
 to the human circulatory system and muscles over extended periods .
there have been positive 
 reports12,13,14 about how advanced 
 cardiorespiratory endurance not only enables one to engage in aerobic exercises , such as 
 walking and jogging for a longer time , but also enhances one s academic accomplishments by 
 improving concentration levels .
there are many methods to evaluate cardiorespiratory 
 endurance considering various aspects such as assessment purpose , targets , and social 
 influences .
a certain method may or may not be superior to another ; however , the paps 
 evaluation method is currently considered an optimal standard method
. continued 
 research15 showed that a solution is 
 required to reduce the gaps among the different methods evaluating cardiorespiratory 
 endurance . in this
regard , skiing has developed as a popular health - improving sport that can 
 facilitate students physical fitness development and provide great exercising benefits .
the 
 ski simulator exercise is a training machine that uses a band to simulate an environment of 
 reduced resistance force between the snow surface and ski plates . due to these mechanical 
 features ,
the ski simulator exercise is considered to have an effect similar to that of the 
 elastic resistance exercises .
anderson et al.16 reported that elastic resistance exercises are more effective for 
 training small muscle groups , such as the muscles of the neck , shoulders , and arms , as 
 compared to the strength training exercises using free weights .
elastic bands undergo a 
 linear increase in tension from the beginning of the contraction to the full range of 
 motion17 .
the tension generated may 
 make it difficult to maintain a balanced posture , thus facilitating the transition to the 
 next movement with a different heart rate as evident from the pei data difference between 
 two groups and exercises .
oloughlin et al.18 emphasized on the absolute lack of physical activities due to 
 increased time spent on video games and computers . on the other hand ,
kim et al.19 claimed that the interest in sports can 
 promote the development of physical fitness by increasing the level of participation in 
 exercises .
the importance of adequate exercising applies to both obese and normal weight 
 children ; therefore , as mentioned in this study , skiing as an ideal sport can be practically 
 utilized in real - life settings .
taking bmi , physical fitness level , and sport durability 
 into consideration , this study showed that the ski simulator exercise could produce a 
 cumulative load even when performed at low intensity .
furthermore , the ski simulator 
 exercise can be effectively utilized as exercise equipment since it resulted in higher pei 
 levels than the harvard step test .
if the schools can increase sport durability by 
 stimulating students interests , the ski simulator exercise can be practically used in 
 programs designed to improve and strengthen students physical fitness .
 [ purpose ] efficient management using exercise programs with various benefits should be 
 provided by educational institutions for children in their growth phase . 
 we analyzed the 
 heart rates of children during ski simulator exercise and the harvard step test to 
 evaluate the cardiopulmonary endurance by calculating their post - exercise recovery rate . 
 
 [ subjects and methods ] the subjects ( n = 77 ) were categorized into a normal weight and an 
 overweight / obesity group by body mass index . 
 they performed each exercise for 3 minutes . 
 
 the cardiorespiratory endurance was calculated using the physical efficiency index 
 formula . 
 [ results ] the ski simulator and harvard step test showed that there was a 
 significant difference in the heart rates of the 2 body mass index - based groups at each 
 minute . the normal weight and 
 the ski - simulator group had higher physical efficiency index 
 levels . 
 [ conclusion ] this study showed that a simulator exercise can produce a cumulative 
 load even when performed at low intensity , and can be effectively utilized as exercise 
 equipment since it resulted in higher physical efficiency index levels than the harvard 
 step test . 
 if schools can increase sport durability by stimulating students interests , 
 the ski simulator exercise can be used in programs designed to improve and strengthen 
 students physical fitness . 