The Use of Heart Rates and Graded Maximal Test Values to Determine Rugby Union Game Intensities : The Journal of Strength & Conditioning Research

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Original Research

The Use of Heart Rates and Graded Maximal Test Values to Determine Rugby Union Game Intensities

Sparks, Martinique; Coetzee, Ben

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Journal of Strength and Conditioning Research: February 2013 - Volume 27 - Issue 2 - p 507-513
doi: 10.1519/JSC.0b013e31825420bd
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Abstract

Introduction

The fitness potential of rugby players can only be optimized if sport scientists and other sport-related professionals understand the diverse nature of rugby and construct sport-specific training regimens accordingly (5). The physiological demands of rugby union are much more complex compared with those of individual sports (7) because of the wide range of movement patterns and the frequent bouts of physical contact that occur during rugby games. The most common methods used in recent years to determine the amount of work and work intensities of rugby games are time-motion analyses (5,6,9,16,17), heart rate recording and analyses (5), as well as blood lactate monitoring (5,16). Time-motion analyses are extensively used to assess the demands of team sports (8). It quantifies the movements of players during matches by dividing the movement patterns into categories (7), such as low-intensity activities (standing, walking, and jogging) and high-intensity activities (cruising, sprinting, and static exertions such as scrums, rucks, and mauls) (5,9,16,17). Although, these studies have provided practitioners with insight with regard to the demands of rugby union games, the validity and accuracy of time-motion analyses have been questioned.

In this regard, Duthie et al. (8) showed that video-based time-motion analyses are only moderately reliable as a tool to determine the demands of rugby union. Furthermore, Duthie et al. (9) concluded that time-motion analyses do not allow researchers to accurately quantify the intensities of movements such as rucks, mauls, and scrums because of the lack of direct intensity measurements. Players will therefore be able to ruck, maul, and scrum without necessarily exerting themselves maximally, despite the fact that these types of movements are generally categorized as high-intensity movements. In view of the named uncertainties concerning the reliability of time-motion analyses, researchers have proposed the measurement and use of heart rates and blood lactate values in an attempt to strengthen the accuracy of the results of time-motion analyses (5,16).

However, the use of blood lactate and heart rate values to determine the demands of rugby union match play have also come under scrutiny. Blood lactate sampling is dictated by stoppages in match play (7), which may negatively influence the accuracy of the blood lactate values. This statement is especially relevant in cases where the time span after high-intensity bouts for blood sampling is too long and the blood lactate is metabolized before measurements are taken. In cases such as these, blood lactate will not give a true reflection of the demands of rugby union matches (7).

Although some researchers have attempted to increase the accuracy of rugby match analyses by monitoring and analyzing rugby players' in-game heart rates (5), certain shortcomings with regard to the use of heart rate values to determine the demands of rugby union games have also come under the spotlight. Individual differences in fitness levels and variations in exercise economy among the players may for example lead to errors when making use of heart rate guidelines alone to estimate exercise intensities and energy system contributions (1). Furthermore, generalizing intensity zones for all players by making use of HRmax may not be the most accurate way of determining the different zones (12).

In view of the aforementioned limitations with regard to the use of time-motion, blood lactate, and heart rate analyses for determining rugby match demands, researchers have been compelled to investigate other suitable methods. One method that has been of particular interest is the combined use of athletes' heart rates and the results of a standard graded maximal oxygen uptake test to the point of exhaustion to determine the competition demands of subjects. The direct measurement of oxygen uptake (V[Combining Dot Above]O2) by indirect calorimetry and specifically by open-circuit spirometry during a graded maximal test allows researchers to identify 2 physiological gas exchange points, namely the aerobic threshold/ventilatory threshold (VT1) and the anaerobic threshold/respiratory compensation point (RCP) (11). The heart rates that correspond to the exercise intensities below the VT1, between the VT1 and RCP and above the RCP are then determined to categorize the intensity zones in low-, moderate- and high-intensity zones, respectively (14). Until now, the last mentioned method has only been used to quantify the competition demands of individual sports such as cross-country running (10), skiing (19), and road cycling (13,18). Currently no attempts have been made to use this method to determine the game intensities of any team sports.

In light of the above-mentioned discussion, which shows that the accuracy of time-motion, blood lactate, and heart rate analyses for determining rugby game intensities can be questioned, the purpose of the present study was to determine the intensities of university rugby union games by making use of the heart rates and graded maximal test values of the players. These results will assist coaches and other sport professionals in gaining a better understanding of what truly happens during rugby union matches.

Methods

Experimental Approach to the Problem

The specific hypothesis under scrutiny was that university rugby games will be categorized by significantly more low- and moderate-intensity activities compared with high-intensity activities. A cross-sectional experimental design was used to test the hypothesis of this study. Subjects were required to complete a standard incremental running test to the point of exhaustion in the period between rugby games. The test was done to obtain the necessary physiological markers and heart rates to classify the different intensity zones. The heart rate values of each player were recorded during 3 rugby games played on the grounds of the institution responsible for the research.

Subjects

Twenty-one male rugby union players from the first and second senior rugby teams of the North-West University (Potchefstroom Campus, South Africa) were selected for this study. The characteristics of the subjects who participated in the study are presented in Table 1. For the players' data to be included in the study, they had to spend at least 50% (one-half) of the game on the field; they had to complete a standard incremental running test to the point of exhaustion at least 2 weeks before or after the game, and they had to be injury free at the time of testing. Each subject was instructed to sleep at least 8 hours during the evening and morning before the different testing sessions. They also had to abstain from ingesting any drugs or participating in strenuous physical activity that may influence the physical or physiological responses of the body for at least 48 hours before the scheduled tests. Subjects had to maintain the same diet during the weeks of testing. The subjects arrived at the testing sessions in a rested and fully hydrated state.

T1-30
Table 1:
Physical characteristics of subjects

All players not adhering to these criteria were excluded from the study. The players' data were collected during 3 separate matches, with between 4 and 9 players monitored during each match. The data were collected during the in-season period that spanned from August to October. The study design, purpose, and possible risks were explained to the subjects, and written informed consent was obtained from the subjects before the investigation. The study protocol was approved by the Ethics Committee of the North-West University.

Procedures

Standard Incremental Maximal Oxygen Uptake (V[Combining Dot Above]O2max) Test to the Point of Exhaustion

A standard incremental maximal oxygen uptake test was conducted by means of open-circuit spirometry and computerized instrumentation in the laboratory. Each of the players performed the standard incremental test to the point of exhaustion on a Woodway Pro XL treadmill (Woodway, Foster Ct, Waukesha, WI, USA). Before each standard incremental test, the players warmed up on the treadmill for 5 minutes at a speed of 10 km·h−1 after which the speed was increased to 15 km·h−1 for a duration of 10 seconds. Static stretches, which involved the following body parts, were then executed for a duration of 20 seconds per stretch: shoulders, arms, chest, and the upper as well as the lower legs. At commencement of the standard incremental test, the first 2 minutes were completed at a running speed of 8 km·h−1, after which the treadmill speed was increased to 10 km·h−1 and by 1 km·h−1 every minute after the first 2 minutes. Exhaled air was continuously sampled by an Oxycon Pro static ergospirometry system (Jaeger Oxycon Pro; Viasys, Yorba Linda, CA, USA) and the rate of oxygen consumption (V[Combining Dot Above]O2), carbon dioxide production (V[Combining Dot Above]CO2), minute ventilation (V[Combining Dot Above]E), and the respiratory exchange ratio (RER) were calculated every 5 seconds by an on-line computer system. The Oxycon Pro was calibrated in accordance with the manufacturer's specifications at the beginning of each test day. The test was stopped if the player indicated that it had to be stopped or if the criteria for reaching the V[Combining Dot Above]O2max value had been achieved (e.g., an RER value greater than 1.10 at test termination; oxygen consumption ceased to rise and reached a plateau or began to fall even though the work rate continued to increase or the maximal age-specific heart rate was reached) (4,15). Throughout the test, heart rate was recorded for each 5-second period by means of a Fix Polar Heart Rate Transmitter Belt (Polar electro OY, Kempele, Finland).

VT1 and RCP

Two physiological gas exchange points were identified. The VT1 was determined using the criteria of an increase in V[Combining Dot Above]E/V[Combining Dot Above]O2 with no increase in V[Combining Dot Above]E/V[Combining Dot Above]CO2 and departure from the linearity of V[Combining Dot Above]E (3). The RCP was taken as the point that corresponds to an increase in both V[Combining Dot Above]E/V[Combining Dot Above]O2 and V[Combining Dot Above]E/V[Combining Dot Above]CO2 (3). Two independent experienced researchers visually detected VT1 and RCP. The different gas exchange phases were used to determine the heart rates that correspond to the 3 exercise intensities (3). Heart rates that corresponded to the exercise intensities below VT1 were classified as low-intensity heart rates; heart rates that corresponded to the exercise intensities between VT1 and RCP were classified as moderate-intensity heart rates; and heart rates that corresponded to the exercise intensities above RCP were classified as high-intensity heart rates (14). Test-retest reliability was determined by means of the Cronbach alpha and values of between 0.877 and 0.938 were achieved for the absolute heart rate at VT1 and RCP, respectively.

Rugby Game Heart Rates

The heart rates of players were recorded at 4-second intervals during matches using the Hosand TM Pro telemetry heart rate monitoring system (Hosand Technologies Srl, Verbania, Italy). An electrode belt was strapped around the chest at the lower sternum of each player before the start of each match. The heart rate signal was then downloaded to a PC during each of the matches. The total match time was made up by the periods of match play activities as well as stoppages in play (excluding the half-time interval), which in certain cases led to total match times being longer than 80 minutes.

Statistical Analyses

The Statistical Data Processing package (20) was used to process the collected data. First, the heart rates obtained from each player during the matches were categorized into the 3 intensity zones (low, moderate, and high) according to the standard incremental oxygen uptake test results. The times spent in the different zones were then expressed as a percentage of the total game time (excluding the time before the games and half-time). Second, the descriptive statistics (averages, minimum, maximum, and SD values) were calculated for each variable. Last, a dependant t-test was done to establish whether significant differences occurred between the intensities of each half. The level of significance for the t-test was set at p ≤ 0.05.

Results

The Standard Incremental Test Values

The results from the standard incremental tests are presented in Table 2. The players achieved an average V[Combining Dot Above]O2max value of 42.7 ± 6.8 ml·kg−1·min−1 with an average HRmax value of 185 ± 7.0 b·min−1. The first gas exchange point, the VT1, occurred at an average heart rate of 153 b·min−1, which was calculated to be 82.7% of the HRmax. However, the RCP occurred at an average heart rate of 169 b·min−1 and at 91.4% of the HRmax. The heart rates for the different intensity zones were determined to be 141–152 b·min−1, 153–169 b·min−1, and 170–185 b·min−1 for the low-, moderate- and high-intensity zones, respectively.

T2-30
Table 2:
Standard incremental test-related measurements of subjects

Match Analyses

Table 3 shows the descriptive statistics for all the match analyses–related measurements. The average heart rate recorded for all the matches was 165 b·min−1, which falls within the moderate-intensity zone when categorized according to the heart rate zones presented in Table 2. Furthermore, the average HRmax achieved during the games was 192 ± 8.8 b·min−1, which is higher than the mean HRmax achieved during the incremental test (185 ± 7.0 b·min−1). Of the total possible game time of 80 minutes, players only spent an average of 56 minute:23 seconds ± 16 minutes:55 seconds on the playing field.

T3-30
Table 3:
Descriptive statistics for all the match analyses–related variables

Figure 1 shows the mean time expressed as a percentage of the total game time that was spent in the different intensity zones during the first and second halves, as well as during the entire match. From Figure 1, it is apparent that players spent the majority of time during matches in the high-intensity zone. There were no significant differences between the percentages of time spent in the different intensity zones during the first halves of the different matches. There was, however, a significant difference between the percentages of time spent in the low- (23.2%) and high-intensity zones (37.4%), respectively, during the second halves of the different matches. With an analysis of the total match time, significant differences (p < 0.05) were observed between the percentage of time spent in the low-intensity compared with the moderate-intensity zones (22.8 vs. 33.6%), as well as the percentage of time spent in the low-intensity compared with the high-intensity zones (22.8 vs. 43.6%).

F1-30
Figure 1:
Time spent in the different intensity zones during the entire match and different halves.

The duration of time players spent in each of the intensity zones are presented in Table 4. The mean total time spent in the different intensity zones during the matches is as follows: 15 minutes:6 seconds, 24 minutes:5 seconds, and 29 minutes:38 seconds for the low-, moderate-, and high-intensity zones, respectively. The mean duration of high-intensity bouts during the entire match was 1 minute:17 seconds, with the mean duration of both moderate- and low-intensity bouts being 29 seconds.

T4-30
Table 4:
Descriptive statistics of the different intensity zones identified for the different matches

Discussion

The use of time-motion, blood lactate, and heart rate analyses for the determination of rugby match demands have been questioned because of the limitations that have been identified. Hence, the purpose of this study was to determine the intensities of university rugby union games by making use of a different method that uses the players' in-game and graded maximal test heart rates as well as other respiratory-related variables.

The results of the study first showed that the players' in-game and graded maximal test heart rates can be used to determine the intensities of university rugby union games. From these results it is also apparent that the players spent more time in the high-intensity zone during match play compared with previous time-motion analyses studies (5,6,9,16,17), which was unexpected. There were significant differences between the percentage of time players spent in the low- and high-intensity zones during the second halves and during the match as a whole, respectively. Significant differences were, however, observed when the percentages of time spent in the low- and moderate-intensity zones during the entire match were compared. The study did not therefore succeed in showing that university rugby games will be categorized by significantly more low- and moderate-intensity activities compared with high-intensity activities.

No other studies have been conducted that had used heart rates and graded maximal test values to determine the intensities of team sport participants during match play. It is therefore not possible to directly compare the results of this study with similar studies. However, several studies have used time-motion, blood lactate, and heart rate analyses to determine rugby game intensities (5,6,9,16,17). However, these studies were performed on professional or elite rugby players and not on university rugby players, which may make comparisons between the results of this study and those of other studies difficult. Still, comparisons between this and another study (5) revealed that the university rugby players in this study spent more of the total game time in the high-intensity heart rate zone (43.6% vs. 58.5%). Also, compared with players in other studies (5,9,17), where the mean duration of high-intensity bouts (work) was seldom higher than 6 seconds, with a few bouts that surpassed 12 seconds, the players in the current study showed a mean high-intensity bout duration of 87 seconds.

When comparing time-motion analysis results of previous studies (6,9,17) with the current study, the approximate amount of time spent (8–10%) in high-intensity activities (e.g., sprinting, cruising, and rucking/mauling) are much less than when in-game and graded maximal test heart rates are used. Therefore, it is evident from the current and previous studies that the anaerobic glycolytic energy system is mainly used, with the aerobic energy system assisting during recovery periods.

Three possible reasons can be provided for the huge disparity that exists between the duration of time spent in the high-intensity heart rate zone by players in this study compared with players of previous studies. First, previous studies only categorized activities into high- and low-intensity activities, with no moderate-intensity activities noted. This study, however, made use of a low-, moderate- and high-intensity categorization. The difference in categorization between this and other studies may have influenced the distribution of intensity zones very differently from that which was reported previously. Second, the use of heart rates to categorize the high-intensity zone allows researchers to get a more accurate reflection of the real physical exertion players perform when executing certain tasks. In most cases, the heart rates will take a few seconds to decrease back to the moderate-intensity range, which will probably increase the period players spent in the high-intensity heart rate zone. In comparison, previous studies used time-motion analyses where high-intensity activities were timed as it took place and the time watch stopped as soon as the activity reached its end. This will definitely lead to shorter time periods in the high-intensity zone when compared with a study where the heart rate–related analyzing method was used.

Third, in cases where researchers used players' data collected before 2000 and 2007 (9,17), when certain rule changes had not yet taken place, the relevance of these results on today's rugby players can be questioned. With regard to the effect of rule changes on the demands of a rugby union game, Williams et al. (22) indicated that rule changes led to a significant increase in ball-in-play time, which will directly influence the game demands by increasing it. This finding was further substantiated by Van den Berg and Malan (21) who discovered a significant decrease in the number of scrums and line-outs as well as a significant increase in the number of tackles made, meters gained, and rucks won during the Super 14 Tournament of 2008 when compared with the values of previous years. They attributed these results to, amongst other things, the rule changes introduced in 2008. All these findings suggest that players would spend more time in the high-intensity zone because of the rule changes that had been introduced.

With regard to the intensity zone heart rates identified by means of the standard incremental oxygen uptake test results, the mean heart rates for categorizing the moderate- and high-intensity zones were calculated to be 82.0 and 91.2% of the HRmax, respectively. These findings are not in agreement with the proposed heart rate–intensity guidelines of 60 and 80% of the HRmax for the corresponding intensity zones (2). From these results, it is clear that general heart rate–intensity guidelines cannot be accurately applied to team sport participants, such as rugby players. Individualized, physiologically determined and sport-specific heart rate–intensity guidelines would therefore be much more accurate and relevant for use among team sport participants.

In summary, to date, research work with regard to the use of more accurate and relevant methods to determine the intensities of team sports is insufficient. The use of more complex training methods among rugby players, as well as the fact that various rule changes have been implemented since 2000, may lead to the emergence of new trends and activity profiles among rugby players during match play. Hence, scientists need to investigate new ways of analyzing and conceptualizing the on-field activities of team sport participants, such as rugby players. This is the first study that has attempted to address this need.

However, the results of the present study must be interpreted with caution because the results are only applicable to university rugby games. The accuracy of this method to determine the demands of rugby union games should thus be measured and tested through more elaborate studies on rugby players of different participation levels. Furthermore, seen from a physiological viewpoint, it should be noted that the standard incremental treadmill test may not be the most suitable method for determining the heart rate–intensity zones for use in analyzing the rugby match demands. Rugby games consist of running different distances, pivoting and making frequent changes in direction while constantly accelerating and decelerating. The movements during the treadmill running test are continuous forward running at constant speeds. The muscle recruitment patterns and energy demands during a rugby match will therefore probably be different from those of the treadmill test. This notion was also substantiated by the difference in the average maximal heart rate values observed between the standard incremental treadmill test and the rugby games. However, until now no other method or test has been designed to determine the heart rate–intensity zones of athletes. This is an aspect researchers need to consider when making use of the proposed method to determine team sport participants' game intensities.

Practical Applications

The use of in-game and graded maximal test heart rates as well as other respiratory-related variables will enable sport scientists and other sport-related professionals to draw more valid conclusions with regard to the demands of a team sport such as rugby union. What the results of this method also show is that sport scientists and conditioning coaches should construct training programs to concentrate primarily on high-intensity activities lasting approximately 1 minute, with 30 seconds rest in between. Therefore, the conditioning of rugby players should mainly focus on the anaerobic glycolytic energy system, but the importance of the aerobic energy system should not be overlooked because the body primarily depends on aerobic energy during the recovery period between high-intensity bouts.

Acknowledgments

The Statistical Consultation Services of North-West University (Potchefstroom Campus) determined the statistical methods and procedures for the analyses of the research data.

References

1. Achten J, Jeukendrup AE. Heart rate monitoring: Applications and limitations. Sports Med 33: 517–538, 2003.
2. Burke ER. Heart monitoring and training. In: Precision Heart Rate Training. Burke ER, ed. Champaign, IL: Human Kinetics, 1998. pp. 1–27.
3. Chicharro JL, Hoyos J, Lucia A. Effects of endurance training on the isocapnic buffering and hypocapnic hyperventilation phases in professional cyclists. Br J Sports Med 34: 450–455, 2000.
4. Davis JA. Direct determination of aerobic power. In: Physiological Assessment of Human Fitness (2nd ed.). Maud P.J., Foster C., eds. Champaign, IL: Human Kinetics, 2006. pp. 9–18.
5. Deutsch MU, Maw GJ, Jenkins D, Reaburn P. Heart rate, blood lactate and kinematic data of elite colts (under 19) rugby union players during competition. J Sports Sci 16: 561–570, 1998.
6. Deutsch MU, Kearney GA, Rehrer NJ. Time-motion analysis of professional rugby union players during match-play. J Sports Sci 25: 461–472, 2007.
7. Duthie G, Pyne D, Hooper S. Applied physiology and game analysis of rugby union. Sports Med 33: 973–991, 2003.
8. Duthie G, Pyne D, Hooper S. The reliability of video based time-motion analysis. J Hum Mov Stud 44: 259–272, 2003.
9. Duthie G, Pyne D, Hooper S. Time-motion analysis of 2001 and 2002 super 12 rugby. J Sports Sci 23: 523–530–2005, .
10. Esteve-Lanao J, San Juan AF, Earnest CP, Foster C, Lucia A. How do endurance runners actually train? Relationship with competition performance. Med Sci Sports Exerc 37: 496–504, 2005.
11. Foster C, Cotter HM. Blood lactate, respiratory, and heart rate markers on the capacity for sustained exercise. In: Physiological Assessment of Human Fitness. Maud P.J., Foster C., eds. Champaign, IL: Human Kinetics, 2006. pp. 63–75.
12. Hills AP, Byrne NM, Ramage AJ. Submaximal markers of exercise intensity. J Sports Sci 16: S71–S76, 1998.
13. Lucia A, Hoyos J, Carvajal A, Chicharro JL. Heart rate response to professional road cycling: The Tour de France. Intern J Sports Med 20: 167–172, 1999.
14. Lucia A, Hoyos J, Carvajal A, Chicharro JL. Physiology of professional road cycling. Sports Med 31: 325–337, 2001.
15. McArdle WD, Katch FI, Katch VL. Exercise Physiology: Energy, Nutrition and Human Performance (5th ed.). Philadelphia, PA: Lippincott Williams and Wilkins, 2001.
16. McLean DA. Analysis of the physical demands of international rugby union. J Sports Sci 10: 285–296, 1992.
17. Roberts SP, Trewartha G, Higgitt RJ, El-Abd J, Stokes KA. The physical demands of elite English rugby union. J Sports Sci 26: 825–833, 2008.
18. Rodriguez-Marroyo JA, Garcia-Lopez J, Juneau C-E, Villa JG. Workload demands in professional multi-stage cycling races of varying duration. Br J Sports Med 43: 180–185, 2009.
19. Seiler KS, Kjerland GO. Quantifying training intensity distribution in elite endurance athletes: Is there evidence for an “optimal” distribution? Scand J Med Sci Sports 16: 49–56, 2006.
20. Statsoft, Inc. Statistica [software]. North West University, 2009.
21. Van den Berg PH, Malan DDJ. The effect of ELVs on the Super 14 rugby union tournament. Master's thesis, North West University, Potchefstroom 2010.
22. Williams J, Hughes M, O'Donoghue P. The effects of rule changes on match and ball in play time in rugby union. Int J Perform Anal Sport 5: 1–11, 2005.
Keywords:

thresholds; game analysis; oxygen uptake

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