Virtual System can be considered interchangeable with shuttle run in healthy children: a cross-sectional study


 Background

Previous studies have evaluated the physiological responses to video game in children with different clinical conditions, however, although no study has compared video game active with an incremental field test in healthy children. The purpose of this study was to compare the maximum heart rate (HRmax) of children, their perceived exertion and motivation during the shuttle run test (SRT) and the Virtual Systems (VS) test, an interactive video game.Methods

This is a cross-sectional study of 235 children (9.0 ± 0.8 years, 109 boys). The two tests were performed one week apart and the children were instructed not to engage in any physical exercise or sports in the 24 hours preceding each test. Their heart rate was monitored at rest for one minute and then throughout the tests. To evaluate the influence of motivation on test execution (SRT and VS), at the end of the tests the children were asked to rate their motivation based on a scale from zero to 10, zero being “not cool” and 10 “awesome”. Perceived exertion at the end of the tests was assessed using the modified Borg scale.Results

HRmax did not differ between the SRT and VS (194.4 ± 10.2 bpm vs. 193.2 ± 13.8 bpm, respectively). Both tests were similar in intensity > and < 96% HRmax. The children showed greater exertion on the Borg scale and motivation during the VS. The multiple logistic regression model showed that motivation (p=0.98), sex (p=0.53), age (p=0.61), nutritional status (p=0.65), and speed (p=0.18) were not predictive factors of whether the child would reach HRmax.Conclusion

The VS can be used as a tool to evaluate the intensity of maximal exercise tests given that the percentage of children who achieved HRmax did not differ between the VS and SRT. The perceived exertion scales were correlated, but only the modified Borg scale correlated with HRmax in the SRT. The tests are motivational, and most children obtained the maximum score in the VS

correlated with HRmax in the SRT. The tests are motivational, and most children obtained the maximum score in the VS Background In recent years, interactive video games, known as Virtual Systems (VS) 1 , have been used for rehabilitation in different areas, such as geriatrics 2 , neurology 3-5 and pediatrics [6][7][8] . In obese children, VS encourage physical activity, thereby reducing sedentary behavior [9][10][11] .
Previous studies have evaluated the physiological responses to video game in children with different clinical conditions 12,13 and the focus of these studies was to compare these physiological responses to active and sedentary video games in children, because Graves et al. (2008) 14 observed that active VG increased physical activity levels in children.
Previous studies have evaluated the physiological responses to video games in healthy children or those with pulmonary disease 8,15 . However, although no study has compared VS with an incremental field test, the Straker and Abbot study, 2007 16 , showed that the HR increased 59% compared to resting HR.
The HR which represents the intensity during exercise 17 , is considered maximum above 180bpm in children, but the maximum threshold used is 200 bpm 18,19 , while Pfeiffer considers a variation between 185 and 225 bpm 20 .
The latest systematic reviews 21,22 of studies on children playing interactive video games have shown an association between an increase in exercise intensity from mild to moderate and a rise in HR. However, it is still unknown whether VS promote vigorous intensity during an incremental exercise test, such as the shuttle run test (SRT).
The most widely used field test to assess aerobic aptitude in healthy schoolchildren is called the SRT. Created in 1982 by Dr Luc Léger et al., it was modified and validated in the area 23-26 . However, in the health area, researchers started to develop new interventions that use active video games 22,27 , indicating them in exercise tests for children as a substitute for sedentary activities, in order to increase physical activity levels and improve the metabolic and cardiorespiratory systems 22 , but no studies have assessed healthy children to determine the expected exercise intensity according to the game used in order to prescribe an adequate exercise program.
The present study was based on the hypothesis that VS would offer a new approach to incremental testing in order to assess maximum heart rate (HRmax), considering possible equivalence between the tests.
The aim of this study was to compare the HRmax of children, their perceived exertion and motivation during an incremental field test, the SRT, and the VS test, an interactive video game test.

Study design and sample
State elementary schools in the city of Sao Paulo, Brazil were randomly contacted to select healthy students aged 8 to 10 years, for this analytical cross-sectional study.
The sample size was calculated based on results obtained in an earlier pilot study conducted with six children that used HRmax as outcome variable. Thus, a sample of 235 children was obtained under the assumption that in the test comparing pairs of means (Student's t-test) for dependent samples, the standard deviation "σ" for HRmax would be 21.16 bpm, with a difference in HRmax between the SRT and VS of 6.33 bpm. We considered a power of 90% and an error of 0.05%.

Protocol
The city of Sao Paulo, Brazil is divided into five regions: east, west, north, south and central. We randomly contacted 5 schools, one from each of these regions, two of which declined to participate. A total of 312 children from the three remaining institutions were invited, 294 of whom completed the questionnaires on medical history and physical activity. Seventeen children were excluded for failing to attend on the day of medical screening, one child refused to be examined, and 34 required further investigations for exhibiting clinical and 12-lead resting electrocardiogram changes. These children were referred to the outpatient clinic for congenital heart defects of the Federal University of Sao Paulo. Of the 242 eligible children, seven who did not appear for testing were considered losses and the remaining 235 were included in the final sample.
The parents first answered a questionnaire on the child's clinical condition and any family history of heart disease. Next, each child was assessed by a cardiologist, who recorded the child's medical history and conducted a physical examination. Blood pressure was measured and an electrocardiogram was obtained with the child at rest, in order to rule out cardiovascular disease.

Body mass index
Body mass index (BMI), calculated by dividing body weight (in kilograms) by height squared (in meters) and expressed as Z score 28,29 , was obtained to assess nutritional status (Table 1). Body weight was measured with the child barefoot, wearing pants and a shirt. Digital scales (G-life ® , Magna, China) were used, with a maximum load of 150 kg and resolution of 100 grams. Height was measured using a wall-mounted measuring tape, with the children barefoot, feet parallel and together, standing upright with their arms extended to the sides of their body and head positioned such that the lower part of the eye socket was at the same level as the earhole.

Shuttle run test
In the SRT, also known as the 20-meter running test, participants run 20 meters. The test starts at a standard speed of 8.0 km/h, increasing 0.5 km/h every minute. The participant was advised of the test pace and a beeping sound signaled progression to the next level.
The step rate was maintained by a standardized recorded beep played on a Toshiba TR8172MU CD player placed 10 meters away. The children were instructed to complete as many stages as possible. The test was stopped when the child was no longer able to reach within three meters of the 20-meter line at the time of the radio signal 30 . The shuttle run test was conducted on a flat surface at the multi-sport courts of the schools.
The 20-meter course was marked with two cones and the children performed the tests individually to avoid their competing with other subjects. The raters accompanied all the tests as a safety measure and to encourage the children to complete the course within the time limits established for each stage. The children were verbally encouraged during each stage using standard phrases such as "you're doing really well" and "keep going" in a clear loud voice to guarantee total comprehension. The completed stages were converted into meters 25,30 .

Virtual System
The VS test was conducted in the school video rooms using the Nintendo Wii ® Free Run video game (Nintendo Company Ltd., Kyoto, Japan, model RVLSWC/RVLSWFSP), part of the Wii Fit Plus set of games. Free Run consists of producing a virtual running field. The Free Run game takes place on an island in the presence of virtual participants, known as avatars. The children run the race at a steady self-determined pace for 20 minutes, with no obstacles or change in intensity.
A predefined path sets the distance in the game, and since an avatar that represents the player in the virtual environment provides the route, the distance in the real world has no relation to the one presented in the game. The player's movements are shown on three accelerometers in the Wii motion plus ® control. The static race provides body movements in the horizontal and vertical plane and the higher the exercise intensity, the greater the distance covered. To ensure reliable results, the researchers monitored the children throughout the test according to the manufacturer's instructions, guiding the placement of the control near the body.
Test run time was determined in the virtual system for a maximum of twenty minutes, preestablished by the investigator for the free racing game. Distance was converted from miles to meters and speed was calculated based on time and distance.
Similarly to the shuttle run, the raters accompanied the tests to ensure the children completed the course until the end of the game and to provide verbal encouragement.
To eliminate any possible motivational influence from the VS, the order of the tests was randomized and the child was asked to choose an envelope, to determine which test (VS or SRT) would be performed first. The envelopes were opaque, sealed and numbered sequentially. The children performed the tests one week apart and were instructed not to engage in any physical exercise or sports in the 24 hours preceding each test.

Heart rate
We used a heart rate monitor (Polar, model RS800CX ® ) to measure HR. The children were monitored at rest for one minute and then throughout the tests. The variables used for statistical analysis were HR at rest and HRmax. A Polar RS800CX ® heart rate monitor was set up using Polar ProTrainer 5 ® software to collect 1-second samples of heartbeats and R-R intervals, in line with the manufacturer's recommendations for maximum accuracy.
The HRmax data used were the values on the heart monitor display at the end of the exercise. Data stored on the heart monitor were transferred to the software at the end of the data collection sessions and the memory cleared to make room for further data collection.
Data recorded on Polar ProTrainer 5 ® software served only for visual verification of the R-R curve. The chart indicated that heart rate increased during the tests and remained around HRmax at the end of the exercise. This initial check was used to ensure that a 1second sample time was not affected by noise from the device.
Resting HR was assessed with the children sitting in a comfortable position with their back and lower limbs supported for 60 seconds, after a 5-minute rest. HRmax, defined as the maximum value attained during the SRT and the VS tests, was 200 bpm or higher 31 .
HRmax was also expressed as percentage of the maximum predicted using the equation

Motivation
To evaluate the influence of motivation on the execution of the SRT and VS, at the end of the tests the children were asked to rate their motivation on a scale from zero to 10, zero being "not cool" and 10 "awesome". Perceived exertion at the end of the tests was assessed using the modified Borg scale.

Statistical analysis
The Kolmogorov-Smirnov test was applied to determine how well heart rate (resting and maximum), the scale of perceived exertion, and motivation adhered to normal distribution.
Descriptive statistics were expressed as means and standard deviations for the numerical variables, and as absolute and relative frequencies for their categorical counterparts. The chi-squared test was used to evaluate the intensity achieved in both tests. The paired Student's t and Wilcoxon tests were applied to compare the SRT and VS for cardiac output and motivational factors, respectively. The independent Student's t-test was applied to compare the perceived exertion obtained with the SRT and VS. Multiple logistic regression was performed to analyze cardiac output by observing whether the child had reached HRmax (≥ 200 bpm), using sex, age, nutritional status, motivation and speed in the VS as predictors. Bland-Altman analysis, which examines the agreement between two methods that measure the same parameter, was applied. It evaluated the difference of means (BIAS) between SRT and VS, to show the agreement between them. The Bland-Altman plot has three lines. The center line is the difference of means, while the upper and lower lines are the limits of agreement, which are calculated as ± 1.96 x SD of the difference of means between both methods. The influence of starting the tests with the shuttle run or the virtual system was analyzed using the nonpaired student's t-test. A 95% confidence interval and significance level of p<0.05 were used for all analyzes. Statistical information was obtained with SPSS statistical software, version 20.0 (SPSS, Chicago, IL, USA).

Results
A total of 235 children were included in the study, 118 started on the VS test and 117 on the SRT. There was no difference in HRmax response (p = 0.056) between the order in which the tests were performed. The sample is characterized in Table 1.
In addition, we observed that both tests were similar for intensity > and < 96% of predicted HRmax (p = 0.50), Table 2.
The children's performance between the SRT and VS tests showed no difference in HRmax (p = 0.18). The difference between the means is illustrated on a Bland-Altman plot ( Figure   1).
A comparison of the children's performance between the tests showed that there was no difference in HRmax (p = 0.18). To assess HRmax agreement between VS and SRT, we plotted the differences against the mean for each subject in a Bland-Altman analysis.The mean difference was 0.1 (p = 0.18) (Figure 1).
According to the results obtained, the number of children motivated in both tests was statistically significant (p < 0.001). However, most of the children (84%) obtained the maximum score (10) in the VS (84%).

Discussion
A similar percentage of children reached HRmax in both tests. There was no difference in HRmax between tests, but mean HR was higher in the VS. The tests were similar in terms of intensity > and < 96% of predicted HRmax. With respect to Borg scale scores, there was greater exertion in the VS when compared to the SRT, and the children were motivated in both tests.
The characteristics chosen for the VS, such as free running with no obstacles or change in intensity, allowed the children to dictate the pace of the exercise. This approach provided a level of intensity corresponding to 83% of estimated HRmax, a value similar to that recommended by the American College of Sports Medicine for prescribing training for children 9,14 .
High-intensity, constant-load exercise protocols are commonly used to assess children's tolerance to exercise 32 . Despite not being an incremental protocol, our findings demonstrate that the virtual system is an innovative instrument as an exercise test, with a constant load profile, in which heart response reaches maximum intensity. This can be confirmed since the children reached maximum HR after 10 minutes, a time similar to that found in protocols using incremental tests, such as the Bruce protocol adapted for children 33,34 .
Physical effort acts directly on heart rate (HR) and is linearly related to exercise intensity 35,36 , exhibiting a strong correlation with maximal oxygen uptake (VO 2 max). As described in an earlier study, VO 2 max is reached when maximum HR reaches 180 bpm 37 .
In the present study, we can infer that the children achieved VO 2 max, since maximum heart rate was above 200 bpm.
The increase in heart rate during exercise can be explained by the rise in sympathetic and decline in parasympathetic tone in healthy children 38,39 . This expected response was observed in the virtual system, since we found a 120% increase from resting to maximum heart rate during the test, which was higher than that reported in studies with games that depend primarily on the lower limbs, whose percentage ranged from 51 to 98% 21 .
Mean heart rate also contributes to a better understanding of the cardiac sytem's response. Straker found an mean HR of 130 bpm in a video game and a value similar to that obtained in basketball and soccer 16 . In his study, children achieved a mean HR of 166 bpm in the virtual system. Using this line of reasoning, we can prescribe video games as a physical activity.
Health promotion aims at a healthy lifestyle via aerobic training from childhood 40 and the basic concept when prescribing physical activity to children is to encourage the habit and interest in routine exercise, prioritizing an entertaining environment 41 .
The characteristics of the game selected for the virtual system, such as free running without obstacles or with changes in intensity, is one of the strong points of the study, since the children themselves determine the pace of the exercise, thereby enabling 83% of estimated maximum HR, a value above that recommended by the American College of Sports Medicine for prescribing physical activity in children 9,14 .
Studies recommend video games with an appropriate frequency and duration for physical training 42 . Thus, the device seems to contribute to physical activity, resulting in an appropriate exercise intensity for children 43 , which disagrees with Graves, demonstrating that video games were not enough to improve their cardiorespiratory aptitude 14 . This may have occurred because most of the games used achieved a much lower than expected heart rate in 51% of adolescents (11 to 17 years old) playing interactive Wii Fit Plus games 44 , 60.7% of 8-10 year olds and 68.3% of [11][12][13][14][15][16][17] year old in Wii Sports Boxing, 63.5% and 70% of 10-13 year-old boys and girls, respectively, also playing Wii Sports Boxing, in addition to 51% in dance games and 59% in a bike game 21 .
In adults, the perceived exertion scales show an association with signs of exhaustion and physiological measurements that include the musculoskeletal and cardiopulmonary systems. According to some researchers, applying perceived exertion scales in small children is difficult, because the rate of cognitive maturation depends on the age of the child and due to the fact that numerical interpretation of perceived exertion is not easily achieved [45][46][47] .
The feeling of tiredness is considered a subjective response that can be influenced by several factors such as the clarity of instructions and the cognitive capacity of the individual 48 . According to Prasad, the use of subjective assessments in children requires them to know the meaning of "out of breath" 49 . Homerding, believes that the modified Borg scale is adequate from the age of 9 years and suggests that the greater the child's functional impairment, the greater the respiratory discomfort and the easier the understanding of perceived exertion 48 .
Children younger than 9 years old have difficulty interpreting perceived exertion scales 48,50 , which may be due to their phase of cognitive development. These findings were confirmed in the present study, since only maximum HR was correlated with the modified Berg scale in the shuttle run.
Studies demonstrate that the virtual system is a motivational instrument for physical activity and that children are motivated by a number of factors during a video game.
These incluse the challenge to finish the game, reach objectives and their interest in the game, in addition to the sensory experience and their control over events [51][52][53] .
Although there are no validated scales to assess children's motivation, the subjects of this study were demonstrably motivated by the tests. As such, new technologies, such as the interactive games of the virtual system, provide a motivational stimulus to children 13 , a fact observed here, since most of the players scored higher in the virtual system compared to the shuttle run.
The main advantage of studying healthy children is the physiological condition of the cardiac system in response to a stress test in healthy children, providing knowledge of heart rate intensity with the virtual system to help in exercise prescription, since it is known that children with heart disease 54 and chronic respiratory diseases 55,56 interrupt exercise early with a reduced HR, which precludes proper evaluation of their cardiac response during SRT and VS.
The main study limitation was the children's difficulty in interpreting the perceived exertion scale, which can be explained by the age range selected. Although two schools refused to participate, restricting the sample to only three regions in the city of São Paulo, we obtained a representative sample.
The findings demonstrate that the virtual system can be implemented as an alternative assessment instrument for maximum exercise intensity for children in school settings and outpatient facilities, without the need of large spaces or substantial investment in equipment. Moreover, video games contribute to the motivational aspect of children because it is an entertaining and easy-to-understand instrument that can be used in rehabilitation programs, possibly leading to greater adherence of children to physical activities.
For future research, the authors suggest studies be designed as clinical trials to rehabilitate children with cardiorespiratory and metabolic disorders in addition to the area of pediatric oncology. We also recommend studying physiological responses with an emphasis on the upper and lower limbs, according to the style of the game selected.

Conclusions
The VS can be used as a tool to evaluate the intensity of maximal exercise tests given that the percentage of children who achieved HRmax did not differ between the VS and SRT. The perceived exertion scales were correlated, but only the modified Borg scale  Tables   Table 1 Sample  Overweight (+1 ≤ z score < +2) 28 12 Obese (z score > +2) 12 5 Figure 1 Methodological agreement by Bland-Altman analysis for HRmax between VS and SRT. The y-axis (Bias) is the difference between heart rate means and the x-axis (Mean) is the individual mean for two tests. The bias was 0.1 log (p = 0.18).