Heart rate (HR) monitoring has become a popular method for measuring exercise intensity (1). Various studies have used the HR to evaluate the cardiovascular responses of Taekwondo (TKD) training. These studies have demonstrated that TKD is an energy demanding intermittent high-intensity sport. The HR is a noninvasive measure that has frequently been used as a reliable index of relative exercise intensity during a variety of intermittent training and competition environments (8,12). This method is based on the principle that there is a linear relationship between HR and steady-state work rate (2,13). Although absolute measures of external load such as the speed and distance coverage are commonly used, the internal load such as the response to the training may be more informative because it provides the interindividual and intraindividual differences that may exist in the way people respond to various modes of exercise.
Two methods based on the HR for quantifying internal training load (TL) are commonly used: Banister's TRIMP and Edwards' TL. Banister et al. (3) proposed a method of quantifying the TL of a training session into an unit ‘dose’ of physical effort. They suggested that a person's HR response to exercise, along with the exercise duration, collectively called a training impulse (TRIMP), may be a plausible measure of effort, because it is based on the extent to which exercise raises the HR between resting and maximal levels (3,11). Edwards' TL is a theoretical modification to the calculation of TRIMP that facilitates the quantification of interval training (7). Although the Edwards' TL method was used in various studies for monitoring TL, there appears to be no evidence that this method of quantification has been validated. Therefore, the aim of this study was to examine the convergent validity between these 2 objective methods. Because the 2 objective HR-based methods calculate the same construct (i.e., TL) using the direct physiological measure of HR, it is hypothesized that these 2 objective methods are interchangeable.
Experimental Approach to the Problem
This study investigated the construct validity of the Edwards' TL method for quantifying internal TL in young TKD athletes. To achieve this, the TL calculated by Edwards' method was compared with that calculated by Banister's TRIMP method for quantifying internal TL. Then, the convergent validity between these 2 commonly used HR to quantify TL was tested.
Ten young elite-level Taekwondo male athletes (mean ± SD, HRmax 198.0 ± 7.1 b·min−1, HRrest 54.2 ± 8.8 b·min−1, and HRreserve 147.9 ± 6.5 b·min−1) took part in the study. These young TKD athletes were members of a regional under-14 representative team competing at the highest level for their age category in Tunisia. All the subjects were in the black belt rank of the Word Taekwondo Federation style and have been competing regularly in national and international competitions for at least 2 years. Each athlete belonged to a body-mass category as classified by the Tunisian Taekwondo Federation (i.e., −34, −38, −42, −45, −48, −51, −55, −59 −63, and +63 kg). Before the study, all the subjects and the parents were informed about the potential risks and benefits associated with participation, and both signed a written informed consent form, agreeing with the protocol procedures and publication of the data. The study was conducted according to the Declaration of Helsinki, and the protocol was fully approved by the Clinical Research Ethics Committee of the National Centre of Medicine and Science in Sports of Tunis, Tunisia before the commencement of the assessments. All the athletes were fully accustomed to the procedures used in this research and were informed that they could withdraw from the study at any time without penalty.
Training data were collected during the 10 weeks of the precompetitive period in a TKD season from September to November 2009. The training program was planned by the coach of the team, and the researchers did not alter the original training program. During this period, young TKD athletes performed TKD training 3 times per week, in sessions of approximately 2 hours' duration. The training included further sessions of individualized work when necessary (range, 6–10 h·wk−1). During each training session, the first approximately 45 minutes of training (including 15 minutes dedicated for warm-up) was generally designed to focus on fitness development, and the remaining time was devoted to the technical and tactical aspects of TKD with approximately 5 minutes of cooldown at the end. TKD training sessions incorporated a combination of the following conventional activities that are universally practiced (6): basic techniques, technical combinations, predetermined sequence of movements (forms), breaking techniques, self-defense techniques, step sparring, sparring (skill) drills, and free sparring with the inclusion of the use of pads and elastics for additional resistance.
All the training sessions were performed in a TKD gymnasium at the same hour of day (i.e., session starting at 18 hours and 30 minutes) in ambient conditions of 15.75 ± 2.97° C, 1,014 ± 7 mm Hg atmospheric pressure, and 87 ± 3% relative humidity. To avoid dehydration, ad libitum drinking was permitted for athletes during all the training sessions. The following instructions were given to athletes: fast for a period of 3–4 hours before the training session, do not ingest stimulants, and hydrate at will.
Training intensity during each TKD training session was recorded using Polar Team HR monitors (Polar Team System, Kempele, Finland), and HR was recorded every 5 seconds. After each training session, HRs were downloaded into a laptop computer using Polar Advantage Software (Polar Electro, Oy, Finland). Resting HR was measured when the athletes were lying on a bed for 10 minutes, after they had woken up (i.e., 5.30 AM). The highest HR value recorded for each athlete at the end of the 20-m shuttle run test (10) was considered to be HRmax.
Edwards' Heart Rate–Based Method
Edwards' TL (7) determines internal load by measuring the product of the accumulated training duration (minutes) in 5 HR zones by a coefficient relative to each zone (50–60% of HRmax = 1, 60–70% of HRmax = 2, 70–80% of HRmax = 3, 80–90% of HRmax = 4, 90–100% of HRmax = 5) and then summing up the results.
Banister's Training Impulse Method
Banister's TRIMP (3) weights the duration using a weighting factor using the following formula:
in which TD is the effective training session duration expressed in minutes and HRR is determined with the following equation: ([HRTS − HRB]/[HRmax − HRB]), where HRTS is the average training session HR, and HRB is the HR measured at rest.
The results are expressed as mean ± SD and 95% confidence intervals (CIs). The normality of data was verified using the Shapiro-Wilk W test. Pearson product moment correlation coefficient with the 95% CI was used to determine the convergent validity between Edwards' TL and Banister's TRIMP. The meaningfulness of correlations was evaluated using Hopkins' (9) classification: r < 0.1, trivial; 0.1–0.3, small; 0.3–0.5, moderate; 0.5–0.7, large; 0.7–0.9, very large; > 0.9, nearly perfect; and 1, perfect. Intraclass coefficient correlation coefficient (ICC), coefficient of variation (CV) and standard errors of the measurements (SEMs) were calculated to establish the reliabilities of Banister's TRIMP and Edwards' TL. Significance was set at p ≤ 0.05.
The TLs were calculated from 284 training sessions. Individual correlations were determined for a minimum of 25 to a maximum of 32 training sessions' data for each athlete. Individual correlations are presented in Table 1. There was a very large to nearly perfect correlations between all individual Edwards' TL and individual Banister's TRIMP. Furthermore, pooled Edwards' TL was very largely correlated with pooled Banister's TRIMP (r = 0.89; 95% CI: 0.86–0.91).
A test for reliability of Edwards' TL and Banister's TRIMP to predict the same value across 2 different TKD sessions of the same intensity was also performed. The ICC of Banister's TRIMP was 0.92 with the 95% CI of 0.61–0.98. The CV and SEM were of 0.44% and 3.67, respectively. The ICC of Edwards' TL was 0.96 with the 95% CI of 0.80–0.99. The CV and SEM were 0.90% and 3.80, respectively.
The correlations between the 2 objective HR-based methods, namely, Edwards' TL (7) and Banister's TRIMP (3) were established to examine the convergent validity of these indicators for quantifying internal TL in young athletes during TKD training. The results showed very large to nearly perfect correlations between all individual Edwards' TL and individual Banister's TRIMP. Indeed, a nearly perfect correlation was observed between pooled Edwards' TL and pooled Banister's TRIMP. These correlations showed that the 2 methods are strongly convergent and confirmed the hypothesis that they are interchangeable during TKD training sessions performed in this study. This agreed with the findings of a previous study of Borresen and Lambert (4) who found a correlation of r = 0.98 (95% CI: 0.96–0.99) between total TL calculated using Banister's TRIMP and Edwards' TL (pooled data) in recreationally trained adults runners aged 30 ± 5 years.
This study also showed that the 2 HR-based methods commonly used have nearly perfect reliability. Some authors considered Banister's TRIMP as a more pronounced measure of TL than Edwards' TL (for a review, see Borresen and Lambert ) Indeed, Banister's TRIMP is considered as a plausible measure of physical effort, because it is based on the extent to which exercise raises the HR between resting and maximal levels. The weighting factor used in the equation of this method emphasizes high-intensity exercise and is also applied to the equation to avoid giving disproportionate importance to long-duration, low-intensity exercise compared with intense, short duration activity (3). This exponential factor is based on the lactate profiles of trained men and women relative to increases in exercise intensity. The ability to quantify TL and reduce training variables to a single figure or factor, as is possible with this equation, is appealing in terms of its practical application (5). To the best of the author's knowledge, there is no evidence that Edwards' TL method has been validated in the literature. Thus, it can be stated that this HR-based method has been derived theoretically and not through experiment. In addition, the linear coefficient relative to each zone (50–60% of HRmax = 1, 60–70% of HRmax = 2, 70–80% of HRmax = 3, 80–90% of HRmax = 4, 90–100% of HRmax = 5) is made theoretically because the individual correlation to the ventilatory and lactic thresholds was not studied. However, this can be accepted because the coefficients used give a proportional weight to the intensity even though these coefficients could have been developed using exponential coefficients (i.e., 1, 2, 4, 7, 9 instead of, e.g., 1, 2, 3, 4, 5). Despite these criticisms, the results of this study provide evidence concerning the construct application and validity of the Edwards' TL method compared with Banister's TRIMP in young TKD athletes.
The results of this study show that the 2 HR-based methods are interchangeable for the assessment of the same construct (i.e., TL). Therefore, it is not necessary to use the 2 methods for comparing objective and subjective (rating of perceived exertion method) methods in future studies and either 1 of 2 objective methods should be sufficient to investigate the relation between other indicators of TL.
This study demonstrates the convergent validity between the 2 objective HR methods, described by Banister (3) and Edwards (7), for the assessment of TL in Taekwondo training efforts, and thus, the construct validity of Edwards' TL is warranted. The results suggest that Banister's TRIMP and Edwards' TL methods are interchangeable. Therefore, either Edwards' TL or Banister's TRIMP can be sufficient to quantify the TL of Taekwondo training with young athletes to investigate the relationship between other indicators of TL. Further studies should investigate if these apply to other sports or efforts and for other age categories.
The authors acknowledge the young Taekwondo athletes involved in this investigation. This study was financially supported by the Tunisian Ministry of Scientific Research.
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