Evaluation of the Efficiency of Estimated Maximum Heart Rate Equations for Regulating Physical Activity Intensity in 8- to 12-Year-Old Students

BRIEF TEXT

Background and Objective

Cardiovascular and sports specialists recommend several indicators, including metabolic equivalents, heart rate, and fatigue indices, for controlling physical activity intensity and workload in exercise, rehabilitation, and occupational settings [1,2]. Among these indicators, heart rate is widely used for regulating exercise intensity; however, maximal heart rate (HRmax) must first be measured or estimated as the basis for calculating exercise intensity and training load. Direct HRmax measurement requires a maximal exercise test on a treadmill or cycle ergometer, but its use may be limited by equipment requirements, time consumption, the possibility of cardiovascular and respiratory problems during incremental exercise, and participants’ reluctance to perform maximal tests [5-8]. Regression equations have therefore been developed to estimate HRmax more simply. The commonly used Fox and Tanaka equations were developed from adult populations, and evidence suggests that equations derived from adults may be inaccurate for children and adolescents [7,14,15]. Several equations have subsequently been developed specifically for children and adolescents. Before these equations are used to regulate safe exercise intensity in schoolchildren, their validity should be evaluated. Therefore, the present study aimed to evaluate the validity of selected HRmax estimation equations in healthy 8- to 12-year-old primary-school students.

Methods

This applied correlational study included 205 healthy boys aged 8 to 12 years who participated voluntarily. Six primary schools from Districts 1 and 2 of Hamadan were selected, considering both relatively advantaged and disadvantaged areas. Because the study was correlational, a larger sample was selected on the basis of previous studies to increase statistical power [19]. A health questionnaire and written informed consent were obtained from the students’ parents. Students with cardiovascular, respiratory, neurological, musculoskeletal, anatomical, or metabolic disorders were excluded. Age, height, body weight, and body mass index (BMI) were measured using standard procedures. After 10 minutes of seated rest, resting heart rate was measured with a Riester 1905 ri-fox pulse oximeter. In 10 participants, resting heart rate was simultaneously measured using a Polar Heart Rate Transmitter T34 to assess the validity of the pulse oximeter; the reported intraclass correlation coefficient was 0.98. Four child-specific HRmax equations were evaluated: Gelbart, Nikolaidis, Mahon, and Shargal [5,16-18]. Direct HRmax was measured using the maximal Bruce treadmill exercise test [20]. Participants were asked to avoid strenuous physical activity for two days before testing, eat their meal three hours before the test, and consume no food other than water thereafter. A chest heart-rate transmitter was used during the exercise test. The highest heart rate achieved during the incremental test was considered measured HRmax. The study also estimated VO2max using the Bruce test equation. Pearson correlation was used to assess the convergence between measured and estimated HRmax, while paired t-test and root mean square error (RMSE) were used to evaluate differences and estimation error. Statistical analyses were performed using SPSS version 26 at P<0.05.

Results

The mean age of the 205 participants was 10.1±1.2 years. Mean height, body weight, BMI, resting heart rate, and estimated VO2max were 142.5±9.5 cm, 37.1±10.1 kg, 18.1±3.3 kg/m², 85.2±8.9 beats/minute, and 43.2±6.1 mL/kg/minute, respectively. The mean directly measured HRmax during the Bruce treadmill test was 203.5±6.2 beats/minute, with a range of 192–222 beats/minute. Mean HRmax estimated using the Shargal, Gelbart, Mahon, and Nikolaidis equations was 201.3±1.1, 202.1±2.5, 202.8±4.0, and 208.3±2.1 beats/minute, respectively; their corresponding ranges were 199–203, 196–208, 192–214, and 204–212 beats/minute. Pearson correlations with measured HRmax were weak: R=0.18 for Gelbart, R=0.17 for Mahon, and R=0.09 for both Shargal and Nikolaidis. The correlations for Gelbart and Mahon were reported as significant, whereas those for Shargal and Nikolaidis were not significant. Significant differences were found between measured HRmax and the estimates from Shargal, Gelbart, and Nikolaidis. Nikolaidis significantly overestimated HRmax, whereas Shargal and Gelbart significantly underestimated it. The mean differences between estimated and measured HRmax were −2.3±6.2 beats/minute for Shargal, −1.4±6.3 beats/minute for Gelbart, 0.7±6.8 beats/minute for Mahon, and 4.8±6.3 beats/minute for Nikolaidis. The difference between the Mahon estimate and measured HRmax was not significant. RMSE values for Shargal, Gelbart, Mahon, and Nikolaidis were 7.4, 7.6, 6.9, and 7.2 beats/minute, respectively. Thus, Mahon had the lowest RMSE and did not show a significant difference from the criterion measurement, but the overall correlations were weak. The findings indicate that the selected child-specific equations showed substantial discrepancies from directly measured HRmax in these Iranian schoolchildren.

Discussion

The present study showed weak associations between HRmax estimated by the selected child-specific equations and HRmax measured by the standard maximal exercise test, with correlation coefficients ranging from R=0.09 to R=0.18. The authors note that a high correlation and absence of a significant difference are important considerations when evaluating the validity of a measurement method; therefore, correlation alone is not sufficient to establish validity. The observed measured HRmax of 203.5±6.2 beats/minute was within the range reported in previous studies of children and adolescents. The significant underestimation produced by the Shargal equation and the significant overestimation produced by the Nikolaidis equation are consistent with findings cited by the authors from previous research [11,27]. The RMSE values, ranging from 6.9 to 7.6 beats/minute, further indicated discrepancies between the estimated and criterion values. The authors therefore concluded that the selected external HRmax estimation equations did not have adequate validity for the Iranian children studied and that equations developed from local populations may be needed.

Conclusion

The selected HRmax estimation equations developed for children did not demonstrate sufficient validity for regulating exercise intensity in healthy Iranian boys aged 8 to 12 years. Although the Mahon equation showed the smallest RMSE and no significant difference from directly measured HRmax, its correlation with the criterion measurement was still weak. Nikolaidis significantly overestimated HRmax, whereas Shargal and Gelbart significantly underestimated it. Considering the discrepancies between estimated and measured HRmax, the authors recommend developing indigenous equations for estimating HRmax in Iranian children.

Keywords: Students; Exercise intensity; Heart rate

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