The purpose of this study is to investigate the relationship between physical efficiency index (PEI) calculated by the Harvard step test and heart rate variation (HRV), and to identify parameters of HRV that can predict PEI in college students. Sixteen college students were participated in this study and they were randomly divided into two groups; higher PEI group (HPEI, n=6) and lower PEI group (LPEI, n=10). To investigate the relationship between PEI and HRV, we were measured HRV and Harvard step test. HRV test was the resting, immediately, 15 min and 30 min after the Harvard step test using electrocardiography device polyGI. Relationship between PEI and HRV were determined Pearson correlation coefficient, and multiple regression analysis was performed for examining HRV parameters to predict PEI. As shown in the result, not only PEI was negatively correlated with root mean squared differences between adjacent normal RR intervals (RMSSD), but had a positive correlation with lowfrequency/highfrequency, but also normalized low frequency (normLF), the ratio of LF, and RMSSD, the change in RR interval showed a significant difference at each time point of measurement according to PEI levels. But, there were no significant differences among the HRV variables except normLF and RMSSD. Our findings suggest a critical information that PEI calculated by the Harvard step test can be used as an index to predict the autonomic nerve function, and high PEI may have a positive effect on changes in autonomic nerve activity during recovery after exercise intervention.
The autonomic nervous system consists of the sympathetic nerve and parasympathetic nerve, and these two nerves work to dynamically maintain homeostasis according to the environment changes. In an emergency, the sympathetic nervous system increases heart rate, respiration, and blood pressure, while turning back to a stable state activates the parasympathetic nerves, leading to the recovery of damaged cells and tissues through energy mobilization (
Heart rate is not stable, but constantly changes in response to physical and mental condition (
Therefore, the present study applied the Harvard step test, which can examine cardiopulmonary function without high test cost, long measurement time, and location restrictions, and we analyzed the changes in PEI and HRV variables during resting and postexercise recovery. The purpose of this study is to investigate the relationship between PEI calculated by the Harvard step test and HRV, and to identify parameters of HRV that can predict PEI in college students.
The participants in this study were 16 college students who did not have cardiovascular and musculoskeletal diseases within the last 6 months were selected. As shown in
HRV was measured for quantitative evaluation of the autonomic nervous system at the resting, immediately, 15 min and 30 min after exercise using by polyGI in biceps brachii (LAXTHA, Inc., Seoul, Korea). HRV was recorded at the time and frequency domain parameters. Time domain parameters were consisted of mean RR intervals, standard deviation of all normal RR interval (SDNN) and root mean squared differences between adjacent normal RR intervals (RMSSD). Frequency domain parameters were consisted of low frequency power (LF power: 0.04–0.15 Hz) and highfrequency power (HF power: 0.15–0.4 Hz) and the LF/HF ratio. All time and frequency domain data were calculated using the Telescan program (ver. 3.03, LAXTHA, Inc.).
Harvard step test was performed on a 50cm bench for male and 40 cm for female, and measured for 5 min at a metronome speed of 120 bpm. After completing the Harvard Step test for 5 min, heart rate was measured between 1 to 1.5 min, between 2 to 2.5 min and between 3 to 3.5 min during the recovery period on the chair. To determine the PEI levels, the three heart rates were summed and then calculated using the following formula: (100×test duration in seconds) divided by (2×sum of heart beats in the recovery periods).
All analyses were performed using IBM SPSS Statistics ver. 23.0 (IBM Co., Chicago, IL, USA). Data were expressed as mean± standard deviation. Pearson correlation coefficient was used to analyze associations of PEI and HRV. Multiple regression analysis was performed to predict the body efficiency index. Statistical significance was considered
As shown in
We conducted multiple regression analysis to predict the PEI, and confirmed the results shown in
As shown in
It has been well known that cardiovascular fitness (VO_{2max}) and autonomic functions are improved by highintensity aerobic exercise intervention (
As shown in the results, in the correlation analysis between PEI and HRV, it was found that PEI had a significant relationship between RMSSD and LF/HF values. RMSSD is a parameter that confirms the rapid change of each RR interval, and since it has a high correlation with HF in the frequency domain, it represents a change in the parasympathetic nervous system (
Monitoring HR and HRV after moderate to highintensity exercise means examining the balance of the sympathetic and parasympathetic nerve activity as well as recovery from physiological stress caused by exercise. The present study showed a significant difference in normLF, the ratio of LF, and RMSSD, the change in RR interval, at each time point of measurement according to PEI levels. Specifically, RMSSD showed statistically significant results in the HPEI group compared to those in LPEI group immediately, 15 min and 30 min after exercise, and normLF showed a significant difference at 15 and 30 min after exercise, excluding immediately after exercise, compared to resting period. These findings indicate that the difference in sympathetic nerve activity before and after exercise depends on the level of cardiovascular fitness. In previous studies that provide important evidence on the relationship between heart rate recovery and HRV in elite athletes,
Our findings suggest a critical information that PEI calculated by the Harvard step test can be used as an index to predict the autonomic nerve function, and high PEI may have a positive effect on changes in autonomic nerve activity during recovery after exercise intervention. However, there are limitations in generalizing the results of this study due to the small sample size. Therefore, research is need to magnify the sample size in the future.
The author received no financial support for this article.
No potential conflict of interest relevant to this article was reported.
Physical characteristics of the subjects
Sex  LPEI  HPEI  Total 

Male  5  3  8 
Female  5  3  6 
Total  10  6  16 
LPEI, lower physical efficiency index; HPEI, higher physical efficiency index.
Change of heart rate variability and physical efficiency index after Harvard step test
Group  1 min–1.5 min  2 min–2.5 min  3 min–3.5 min  PEI 

LPEI (n=10)  66.10±1.20  57.60±2.41  54.60±2.67  83.80±1.99 
HPEI (n=6)  61.00±2.53  53.33±2.16  50.50±1.52  90.50±2.74 
Total (n=16)  64.19±3.08  56.00±3.10  53.06±3.04  86.31±4.01 
Values are presented as mean±standard deviation.
LPEI, lower physical efficiency index; HPEI, higher physical efficiency index; PEI, physical efficiency index.
Correlation between PEI and HRV
Variable  PEI  LF  HF  VLF  TP  RMSSD  SDNN  normLF  normHF 

LF  −0.30  
HF  −0.17  −0.79^{**}  
VLF  −0.22  0.32  0.07  
TP  −0.32  0.10  0.40  0.82^{**}  
RMSSD  −0.56^{*}  −0.05  0.63^{**}  0.58^{*}  0.84^{**}  
SDNN  −0.43  0.07  0.46  0.79^{**}  0.97^{**}  0.89^{**}  
normLF  0.49  0.22  −0.49  0.02  −0.10  −0.44  −0.12  
normHF  −0.49  −0.22  0.49  −0.02  0.10  0.44  0.12  −1.00^{**}  
LF/HF  0.51^{*}  −0.86^{**}  0.55^{*}  −0.26  −0.08  −0.12  −0.06  0.31  −0.31 
PEI, physical efficiency index; HRV, heart rate variability; LF, low frequency; HF, high frequency; VLF, very low frequency; TP, total power; normLF, normalized low frequency; normHF, normalized high frequency; LF/HF, low frequency/high frequency ratio; RMSSD, square root of the mean of the sum of the squares of differences between adjacent NN intervals; SDNN, standard deviation of all NN intervals.
Heart rate variability predicting physical efficiency index
Variable  Adj 
Unstandardized coefficients  Standardized coefficients  


 
Beta  Standard error  Beta  
RMSSD  0.31  0.26  0.31  −0.16  0.06  −0.51  −2.589^{*} 
 
LF/HF  0.51  0.44  0.20  0.18  0.08  0.45  2.286^{*} 
RMSSD, square root of the mean of the sum of the squares of differences between adjacent NN intervals; LF/HF, low frequency/high frequency ratio;
Difference of RMSSD, normLF, LF/HF according to PEI
Variable  Source  DF  SS  MS  

RMSSD  Intercept  1  3,355.75  3,355.75  141.43^{***} 
Group  1  8.61  8.61  0.36  
Error  14  332.17  23.73  
Period  3  4,525.857  1,508.619  33.701^{***}  
Group×period  3  720.394  240.131  5.364^{**}  
Error (period)  42  1,880.112  44.765  
 
normLF  Intercept  1  28,650.65  28,650.65  5,169.47^{***} 
Group  1  4.34  4.34  0.78  
Error  14  77.59  5.54  
Period  3  453.931  151.310  15.356^{***}  
Group×period  3  104.900  34.967  3.549^{**}  
Error (period)  42  413.835  9.853  
 
LF/HF  Intercept  1  47,407.66  47,407.66  241.55 
Group  1  5.83  5.83  0.03  
Error  14  2,747.75  196.27  
Period  3  2,013.353  671.118  10.380  
Group×period  3  389.315  129.772  2.007  
Error (period)  42  2,715.562  64.656 
RMSSD, square root of the mean of the sum of the squares of differences between adjacent NN intervals; normLF, normalized low frequency; PEI, physical efficiency index; DF, degrees of freedom; SS, sum of squares; MS, mean sum of squares; LF/HF, low frequency/high frequency ratio.
Comparison of HRV between LPEI and HPEI
HRV  Period  LPEI  HPEI  Total  Group × period 

LF  Resting  10.89±13.96  6.03±1.17  9.07±11.11  
Immediately  9.73±14.56  5.41±0.39  8.11±11.48  
After 15 min  8.66±11.29  5.28±1.16  7.39±8.93  
After 30 min  10.39±13.32  5.48±1.06  8.55±10.63  
 
HF  Resting  5.76±1.99  5.11±0.69  5.51±1.62  
Immediately  3.56±1.25  4.32±0.59  3.85±1.09  
After 15 min  2.95±1.35  3.68±0.63  3.23±1.17  
After 30 min  4.02±1.49  4.51±0.73  4.20±1.26  
 
VLF  Resting  6.81±0.49  6.43±0.93  6.67±0.69  
Immediately  7.94±0.47  8.13±0.40  8.01±0.44  
After 15 min  5.50±0.61  5.89±0.42  5.65±0.56  
After 30 min  6.35±0.56  6.27±0.55  6.32±0.54  
 
TP  Resting  2,412.78±916.47  1,825.74±1,768.84  2,192.64±1,277.90  
Immediately  3,343.03±1,592.17  3,920.55±1,420.05  3,559.60±1,508.83  
After 15min  536.14±411.67  792.55±563.33  632.29±473.18  
After 30min  1,230.14±418.63  1,076.28±708.31  1,172.44±527.55  
 
normLF  Resting  51.01±3.17  53.90±2.25  52.09±3.13  Resting  Immediately, 
Immediately  56.06±3.18  55.72±2.33  55.93±2.81  
After 15 min  61.66±5.22  58.74±2.78  60.56±4.58  
After 30 min  58.62±4.22  54.67±3.07  57.14±4.21  
 
normHF  Resting  49.00±3.17  46.10±2.25  47.91±3.13  
Immediately  43.94±3.18  44.28±2.33  44.07±2.81  
After 15 min  38.34±5.22  41.26±2.78  39.44±4.58  
After 30 min  41.38±4.22  45.33±3.07  42.86±4.21  
 
LF/HF  Resting  43.81±12.13  52.95±4.24  47.23±10.73  
Immediately  54.24±15.23  56.54±4.78  55.10±12.17  
After 15 min  66.11±26.09  63.30±6.29  65.06±20.58  
After 30 min  58.22±19.95  54.59±6.06  56.86±15.95  
 
RMSSD  Resting  36.02±12.40  22.57±12.32  30.98±13.71  Resting  Immediately, 
Immediately  6.35±3.98  7.86±3.08  6.91±3.64  
After 15 min  7.99±4.48  10.28±5.32  8.85±4.77  
After 30 min  12.50±5.35  16.09±7.70  13.85±6.34  
 
SDNN  Resting  53.06±10.63  41.90±20.59  48.88±15.50  
Immediately  61.38±13.68  67.78±13.90  63.78±13.67  
After 15 min  23.26±6.74  27.31±9.18  24.78±7.71  
After 30 min  35.37±5.79  32.50±11.30  34.30±8.05 
Values are presented as mean±standard deviation.
HRV, heart rate variability; LPEI, lower physical efficiency index; HPEI, higher physical efficiency index; PEI, physical efficiency index; LF, low frequency; HF, high frequency; VLF, very low frequency; TP, total power; normLF, normalized low frequency; normHF, normalized high frequency; LF/HF, low frequency/high frequency ratio; RMSSD, square root of the mean of the sum of the squares of differences between adjacent NN intervals; SDNN, standard deviation of all NN intervals.