Evaluation of oxygen consumption and energy consumption by heart rate index method in soccer players

This study was carried out to determine the validity of the heart rate index (HRindex) method in calculating the maximal oxygen consumption (VO2max) and energy expenditure of different intensity in soccer players. 54 male soccer players who took part in the competitions for at least 3 years participated in the study voluntarily. After the Resting Heart Rate (HRres) measurement, submaximal and maximal oxygen consumption was measured in the treadmill with the indirect calorimetric method (IC) in an increasingly intense exercise protocol. During the test, oxygen consumption (VO2) and HR values were recorded at each workload of the participants. The HRindex value was calculated from the HRexercise/HRres. Using HRindex values, energy expenditure was estimated at intensities corresponding to VO2max and reserve HR (HRr) < 75%, 75-90%, and > 90%. Regression analysis was performed for the relationship between HRindex and VO2 as MET, calculated for each participant at each rate. Differences between measured and estimated VO2max and energy expenditure values at 3 different intensities (<75% HRr, 75-90% HRr, and >90% HRr) were determined by Paired t-test. The mean difference (bias) between measured and calculated VO2max and energy expenditure and the lower and upper limits of consistency was determined by the Bland-Altman plotting method. At the same time, the level of agreement between the measured and calculated variables was determined by Lin's Concordance correlation coefficient (ρc). A highly significant correlation was found between MET (VO2) and HRindex values (r = 0.721; p = 0.000). The VO2max estimated by the HRindex method was significantly lower (11.1%) (p = 0.000). Similarly, the energy expenditure calculated by the HRindex method at each severity was significantly lower than the IC (for <75% HRr t = 10.17; p = 0.000, for 75-90% HRr t = 6.37; p = 0.04 and for >90% HRR t = 3.52; p = 0.001). Bland-Altman plotting showed that the absolute difference between the limits of consistency for VO2max was large. The relationship (trend) between the mean and differences of the calculated and measured energy expenditure values at all intensities is significant (for < 75% HRr r = -0.36; p = 0.000, for 75-90% HRr r = -0.44; p = 0.000 and for > %90 HRr r = -0.33 for; p = 0.000). Lin's Concordance correlation coefficient between IC and HRindex method ρc = 0.05 for VO2max, ρc = 0.48 for <75% HRr, ρc = 0.26 for 75-90% HRr, ρc = 0.42 for >90% HRr and weak for all intensities. The finding of this study showed that thr HRindex method can not be used to estimate VO2max in soccer players, but it can be used to evaluate energy expenditure at different intensities. Keywords: Soccer, Heart Rate Index, Energy Expenditure, Maximal Oxygen Consumption