Badminton, like other racket sports and ball games, relies on discipline-specific technical and tactical skills, but for elite players, the movement pattern characterizing the game also seems to require a high discipline-specific physiological performance profile (4,7,10). Match play is intermittent and characterized by intensive rallies (2,8–10) interspersed by short breaks. Total match duration may surpass 1 hour in international men singles matches (as observed across all Super Series tournaments in 2015, www.tournamentsoftware.com), but most of the points are decided in less than 15 seconds (2,7–9,24).
Simple sprint and jump tests fail to discriminate between elite badminton players and players with a lower performance level (subelite badminton players; see References 4, 16, 23, 29 for details), suggesting the importance of training and test specificity in badminton. Accordingly, improvements in specific agility tests is observed with no changes in simple sprint tests after badminton-specific repeated-sprint training in players at a national level (31). Therefore, the applicability of nonspecific tests may be limited because they do not resemble the physiological demands and the movement patterns of relevance for actual badminton match play (4,8,16,32,33,35).
We recently compared sprint performance and maximal on-court movement speeds with a badminton-specific speed test (23) and observed no differences in sprint performance between elite badminton players, skilled players, and nonbadminton players (active young men with limited badminton experience). Conversely, when tested with the badminton-specific speed test (23) developed to mimic actual match play, elite players were significantly faster than the skilled players and nonbadminton players. Although the speed test seems suitable for assessing maximal movement speeds during on-court actions that resemble match play, the test duration is only ∼1/2 minute and does not allow for evaluation of the players' badminton-specific endurance capacities.
Although explosive movements in a single rally or action apparently rely on the player's alactacid anaerobic power and neuromuscular parameters, the ability to resist fatigue and repeat intense actions throughout the game depends highly on the player's endurance capacity (2,7,13,27). Peak aerobic power in competitive badminton players have been reported to be at ∼60 ml·kg−1·min−1, and players use their aerobic capacity to achieve maximal heart rates (HRs) during the most intense periods of a game with an average HR of ∼85%, signifying the typical aerobic load during match play (2,8,9). The aerobic energy contribution may not only supply energy for ATP resynthesis during the exercise periods but also be of major importance for the ability to recover between rallies and resist fatigue when considering the full match length (2,4,7,8). Laboratory-based endurance tests are commonly applied to evaluate athletes' general aerobic potential (19,20), but a specific approach with field-based methods seems better suited for evaluation of the demands of complex intermittent sports (7,10,34,35). In badminton and other racket sports, it has been reported that specific endurance tests provide better information than nonspecific endurance tests (4,5,7,8,10–15,32–35). A badminton-specific endurance test would provide physiologists and coaches with an evaluation tool to track training specific improvements, and it may be used to set standards for players' on-court badminton-specific endurance capacities.
A number of physiological tests developed for badminton players have been reported in the literature (4,7,10,13,15,16,29,31,35), but apparently, these tests have not adequately reflected the physiological demands or sufficiently mimicked the exercise pattern of badminton match play. Based on our experience from the recently developed badminton speed test (23), which uses a randomized exercise pattern with specific movements and timing resembling match play, we wanted to design an endurance test with an analogous approach and a work-to-rest ratio reflecting the demands in men's international singles matches. The present study describes the development of the badminton-specific intermittent endurance (B-ENDURANCE) test and reports the specificity and reproducibility of the test. The intention of the study was to develop a test of specific relevance for badminton, but we suggest that the test design may be adopted by other sports characterized by an intermittent exercise pattern including accelerations, decelerations, explosive movements, and constant changes of direction.
Experimental Approach to the Problem
The study was designed and conducted to develop a test for evaluating badminton-specific endurance capacity in badminton players and subsequently to evaluate the reproducibility and ability of the test to differentiate between elite and subelite badminton players and trained nonbadminton players. Subjects were instructed to abstain from strenuous exercise 24 hours before testing and to attend all tests well hydrated.
To evaluate the specificity of the test, we compared performance in the developed B-ENDURANCE test with a nonspecific intermittent endurance test (Yo-Yo intermittent recovery level 1 [IR1] test) (17). Thirty-four healthy, men subjects were recruited and divided into 3 groups based on their badminton experience and performance level. The first group consisted of 17 elite men badminton players defined as singles players within the top 100 on the men's single ranking compiled by the National Danish Badminton Association (7 elite players performed both tests [B-ENDURANCE & IR1], and an additional 10 elite players were included in the testing of the B-ENDURANCE test to increase the statistical power of the correlation analysis—see Statistical Analyses). All elite badminton players were daily engaged in organized badminton training. The second group consisted of skilled men badminton players defined as competitive single players with a ranking position higher than 100 on the Danish men's single ranking and with regular participation in individual and/or the Danish team tournaments. All skilled badminton players were weekly engaged in organized badminton training. The third group consisted of trained nonbadminton players defined as physically active men matched to the 2 other groups for age and stature. All nonbadminton players were engaged in weekly exercise training, but with no previous record of participation in organized badminton training. For all groups, tests were completed at similar times of the day (individual subjects were scheduled within ∼2 hours on different experimental days) with at least 72 hours between tests.
Reproducibility of the test was evaluated for 9 of the men badminton players (6 elite and 3 skilled players). Each of these players completed 3 trials of the B-ENDURANCE test on 3 separate days interspersed by at least 72 hours and a maximum of no more than 14 days. The evaluation of the reproducibility was performed on the same time of the day (scheduled within ∼2 hours for each individual), whereas different times of day were used for testing of individuals.
The developing phase included review of literature (2,7–10,13–15,22–24,28–31,35), video analysis of international elite matches, and pilot experiments and experience from a previously developed badminton speed test (23). Based on reviews of relevant studies, it became clear that badminton is a game of intensive short rallies interspaced by ∼10–15 seconds rest time (2,8,9,21), whereas previously developed tests usually consist of longer working periods, which do not reflect the demands of badminton (8,10,13,35). Video analysis and pilot experiments showed that the time between sequences and levels would mimic real match situations when using a computer with a visual countdown, randomized sequences, audio beeps, and influence from various sensor positions. The randomized movement pattern, with the sensors placed in each of the 4 corners of a badminton court, provided a more appropriate movement pattern to badminton and the ability to distinguish between elite players and nonbadminton players. Two sensors where placed on the front court 60 cm from the net and 50 cm above the floor on the single line. Two sensors where placed at the back of the court 200 cm above the crossing of the double serve line and the single sideline. The placement of sensors and timing of the actions was aimed at creating an incremental exercise test where the movement pattern reflects the demands of international men's singles.
Seven elite players with an age, height, and weight of 27 ± 3.7 (±SD) years, 184.7 ± 8.2 cm, and 77.1 ± 7.9 kg, respectively; 9 skilled players with an age, height, and weight of 25.8 ± 5.1 years, 183.0 ± 4.7 cm, and 79.2 ± 5.6 kg, respectively; and 8 nonbadminton players with an age, height, and weight of 28.1 ± 3.8 years, 183.1 ± 8.2 cm, and 78.9 ± 8.2 kg, respectively, participated in the study. The elite players were recruited from Team Denmark national team training, International Badminton Academy, and Stenhus Badminton College. Furthermore, 9 healthy, men badminton players with an age, height, and weight of 21 ± 2.95 years, 184.3 ± 3.97 cm, and 76.3 ± 6.6 kg, respectively, completed 3 additional rounds of testing to determine test-retest variation with and without a familiarization trial. All participants were fully informed of all experimental procedures and any discomforts associated with participating and signed a written informed consent before enrollment in the study. This study conformed to the Code of Ethics of the World Medical Association (Declaration of Helsinki) and was approved by the ethical committee of The Capital Region of Denmark (H-4-2012-FSP).
Subjects in the first part of study completed 2 test days with a minimum of 72 hours between and were randomly assigned to either perform the IR1 or B-ENDURANCE test on the first test day and the complementary test on the second test day. Before the tests, subjects completed an 8-minute standardized warm-up and the initial 3 levels of either the IR1 or B-ENDURANCE test (level 1.1; 2.1; 3.1 corresponding to ∼2 minutes) to become familiar with the relevant tests. The subjects then rested for 4 minutes before commencing the entire test. During all tests, subjects were instructed to perform maximally and verbal encouragement was given on all test days. Time to exhaustion was recorded as the performance parameter and HR was continuously registered for each subject using a Polar HR monitor FS2c with matching T-31 HR belts (Polar, Kempele, Finland).
Badminton Endurance Test
The B-ENDURANCE test consists of 12 levels (level 1–12) and made up of a number of sequences (1–6). Each sequence consists of 8 badminton-specific actions toward custom-made sensors (Larsen Elektronik, Praestoe, Denmark) positioned at each of the 4 corners of the singles badminton court (Figure 1). The movement pattern during each action is randomly generated by a computer program (Direct RT 2008; Empirisoft Corporation, New York, NY, USA) and the sensor to hit is shown on a monitor placed at the net in the middle of the court.
Levels 1 and 2 consists of 1 sequence, levels 3 and 4 of 3 sequences, and levels 5 to 12 have 6 sequences, with the tempo gradually increasing from each level to the next. The subject starts a sequence from the center of the badminton court, and time to complete a sequence decreases progressively from 30 seconds per sequence at level 1–28 seconds per sequence at level 2. From levels 3 to 12, the total time to complete a sequence decreases by 1 second from 27 seconds at level 3–18 seconds at level 12. In each sequence, a visual countdown (the numbers 3, 2, 1) is displayed during the recovery time between sequences (i.e., when returning to the center of the court). The countdown is included to give subjects timing and rhythm analogous to real play. Between each sequence, a visual countdown from 10 seconds is displayed. Subjects are requested to hit all sensors from behind, similar to a real badminton stroke. The test is terminated the second time a subject fails to reach a sensor within a sequence, and total time is recorded as the test result.
Data from our recently developed badminton speed test (23) identified that subjects use ∼3/5 of the given time to react, move, and hit a given sensor and ∼2/5 of the time to return to the center of the court. Because subjects in level 1 has 30 seconds to complete 8 actions, there is a total of 3.75 seconds per action, allowing subjects ∼2.25 seconds (3/5) to react, move, and hit a given sensor and ∼1.5 seconds (2/5) to return to the center of the court. In level 12, subjects have 2.25 seconds per action, allowing them 1.35 seconds (3/5) to react, move, and hit a given sensor and 0.9 seconds (2/5) to return to the center of the court.
Yo-Yo Intermittent Recovery Test Level 1
The IR1 test was performed by all subjects to evaluate endurance capacity in a non–badminton-specific test. It consists of 2- × 20-minute running at progressively increasing speeds controlled by audio bleeps from a CD player. Each run is separated by an active recovery period of 10 seconds. When the participant failed to reach the finishing line in time for the second time, the total time was recorded as the test result (17).
Group differences in performance, anthropometrics, and physiological characteristics were evaluated with a one-way analysis of variance. In the case of a significant difference in mean values, the Tukey post hoc test was used to determine significant differences between the test groups. The coefficient of variation (CV) was calculated as a measure of test reproducibility being the SD between tests divided by the average test result. All values are presented as mean ± SD unless otherwise specified. The significance level was set at p ≤ 0.05 and power analysis based on pilot studies, and experiences from our recently developed speed test indicated that detecting differences in performance between the 3 groups would require a sample size of approximately n = 7 in each group. However, to increase the statistical power of the correlation analysis between ranking position and player's performance in the B-ENDURANCE test, we included an additional 10 elite players in the testing and as described for the B-ENDURANCE test. These players did not complete the running test, and their data were only included in the linear correlation analyses between ranking position and the B-ENDURANCE test performance as evaluated with Pearson's product-moment correlation testing.
The B-ENDURANCE test performance was 1,332 ± 160 seconds for the elite group, which was better (p ≤ 0.05) than performance for the skilled players (897 ± 140 seconds) and nonbadminton players (765 ± 200 seconds; Figure 2). No significant difference was observed between skilled players and nonbadminton players.
When national single ranking position for all badminton players in the study (elite and skilled) was plotted against the B-ENDURANCE test performance, a significant correlation (n = 26, r2 = 0.78, and p < 0.0001; see Figure 3A) was observed. This also applied if only data for the elite group were analyzed (n = 17, r = 0.8, and p < 0.0001; Figure 3B).
The IR1 test performance was 1,188 ± 174 seconds for the elite players, which was significantly better (p ≤ 0.05) than the skilled players (739 ± 136 seconds) and the nonbadminton players (829 ± 290 seconds). In contrast to the B-ENDURANCE test, no correlation was observed between the IR1 test performance and elite badminton players ranking position (n = 7, r = 0.37, and p = 0.48).
Maximal HR was not different between trials (trial 1: 192 ± 11 b·min−1, trial 2: 192 ± 12 b·min−1, and trial 3: 192 ± 11 b·min−1) (Figure 4).
For the B-ENDURANCE test, the CV was 7.9% when comparing the first and second trial in 9 badminton players. However, CV was reduced to 2.5% when comparing trials 2 and 3 (Figure 5).
In the present study, we have developed and examined the reproducibility and relevance of a novel intermittent badminton endurance test consisting of movements and exercise intervals that resembles match play. The B-ENDURANCE test performance was superior in elite players compared with nonelite badminton players, and the B-ENDURANCE test performance correlated to the players' national ranking positions for men's singles, signifying the badminton-specific relevance of the test. Furthermore, test-retest reproducibility was quite high when subjects were accustomed with the B-ENDURANCE test and the CV reduced from 7.9 to 2.5% when a familiarization trial was included. From a practical point of view, we suggest that the B-ENDURANCE test may be used by physiologists and coaches for cross-sectional comparison of players and for evaluation of longitudinal changes, e.g., individual training adaptations.
The specificity of a test is markedly improved when it includes an exercise pattern that resembles actual match play (3,4,12,23). The necessity to include badminton-specific movements is supported by the present observations of no correlation between elite players ranking position and performance in the nonspecific running test. For the B-ENDURANCE test, we observed fairly high correlation coefficients between test performance and players' single ranking positions, both when all ranked players were included and when only elite players were included in the analysis. However, considering the relatively low sample size and that a simple correlation analysis of cross-sectional data only provides an indication of a relationship between the factors, the findings should be interpreted with caution. Superior B-ENDURANCE test performance in the higher ranked players does not necessarily imply that enhancing endurance performance will improve the players' ranking positions. It is only indicative of the necessity to possess a high endurance capacity for elite single players.
Including badminton-specific movements does not seem to be the only prerequisite to achieve high test validity. In comparison with previously described on-court tests for evaluation of endurance capacity in elite and subelite badminton players, we observed a closer correlation between test performance and players' performance levels, as indicated by their national or international single ranking position (4,10). This may in part relate to differences in the length of the intervals in the present and previous tests. Both Fuchs et al. (10) and Chin et al. (4) reported moderate correlations between badminton endurance tests and ranking position. Although both studies were performed on the court with movements mimicking match play, the work periods were much longer than those normally observed during singles matches and that may change how specific the tests challenge the energy-generating systems of importance.
Phosphocreatine levels and the aerobic capacity to resynthesize high–energy-generating phosphate stores between intense sequences seem to be of major importance for high-intensity intermittent exercise capacity (1). In this context, Chin et al. (3) reported that elite badminton players have higher explosive power during 10-second all-out cycling than squash, tennis, football players and road cyclists (when adjusted for body weight), suggesting that badminton players possess high alactacid anaerobic power in addition to their aerobic capacity. The exercise-to-rest ratio in badminton is usually ∼1:2 with most of the rallies ranging from a few seconds to half a minute (2,8,9). If the exercise duration or work-rest ratio in a test is markedly different from match conditions, it may compromise the relevance and significance of the test.
When comparing results from the previous badminton specific speed test (B-SPEED) (23) with the last completed level of the B-ENDURANCE test, it seems that for the elite badminton players, movement speeds required during the final level of the B-ENDURANCE test are close to the maximal movement speeds achieved by elite players in the SPEED test. However, the skilled badminton players finish at significantly lower levels in the B-ENDURANCE test, although their B-SPEED performance would allow for completing faster levels if they possessed the endurance capacity necessary to recover between exercise sequences. This indicates that the superior performance in elite players relies on a highly developed endurance capacity that even under maximal cardiovascular stressing allows them to recover between intense actions and maintain very high intensity/speed during short exercise periods.
The exercise and recovery periods in the IR1 test are comparable with those of the B-ENDURANCE test and may represent a relevant exercise pattern for many intermittent sports. Furthermore, all 3 groups obtained similar peak HRs in the 2 tests indicating that the B-ENDURANCE test, analogously to the IR-1, taxes the subject's maximal aerobic capacity (17).
However, as discussed above the specificity is lacking because running does not resemble badminton movements and activation of the specific muscle groups used during badminton play. In elite badminton players, a higher cross-sectional area is observed in both type I and II fibers of the dominant leg compared with the nondominant leg (27). Elite badminton players have maximal concentric muscle tension in m. quadriceps in the dominant leg, which is higher than the corresponding values measured in tennis and football players and cyclists (3). Also, Mikkelsen (27) observed higher muscle strength and elevated myoglobin and oxidative enzyme activity in the dominant legs of elite badminton players compared with athletes in sports where the movement pattern is more symmetrical (4,27). The B-ENDURANCE test, which targets the specific physiological adaptations for badminton players especially in the dominant leg (equivalent to the racket hand), may indeed be more valid in contrast to the nonspecific IR1 test. However, not only the inclusion of badminton-specific movements but also the randomized exercise pattern may be of major importance when developing a badminton-specific test (23). Although experienced players may anticipate some shots from their opponent, real match play indeed involves stochastic movements in unknown directions and if tests, instead of a randomized movement pattern, use a stereotypic (known) pattern, it will compromise the specificity of the test.
However, the randomized movement pattern may compromise test reproducibility if a familiarization trial is not included. Thus, the CV in the B-ENDURANCE test between the first trial and the second trial was moderate (7.9%) compared to the CV reported in continuous and intermittent endurance tests (∼4%) (6,17,18). Furthermore, 8 of 9 subjects improved their performance from the first to the second test, demonstrating that there is a marked familiarization effect associated with the B-ENDURANCE test.
Consecutive trials in more simple exercise tests, such as time-trial cycling on a stationary ergometer, may also lower test-retest variation with the largest effect observed from trial 1 to trial 2 (20). Therefore, players should be familiarized with the B-ENDURANCE test before the first round of testing when evaluating longitudinal changes. Accordingly, with the inclusion of a familiarization trial, there was no systematic difference/improvement from trial 2 to trial 3 and CV was reduced to 2.5%, which is comparable to the variation reported in both continuous and intermittent endurance tests (17,25,26,33). If this premise is fulfilled, it seems that B-ENDURANCE test is reproducible and that coaches and physiologists may apply the test to evaluate training effects, identifying potentially weak points in relation to the players' physical exercise capacities. Hence, the test is suitable for optimizing and evaluating elite badminton players' physical fitness statuses.
In conclusion, the B-ENDURANCE test performance correlated to Danish elite badminton players' positions in the national ranking for men's singles and was capable of discriminating between the test endurance performance of elite and nonelite badminton players. When including 1 familiarization trial, test-retest CV is lowered 2.5%, which is of a magnitude similar to other highly esteemed endurance tests (i.e., the Yo-Yo IR Test).
Our results show differences between a group of elite and nonelite players badminton players in the B-ENDURANCE test performance. Performance seemed to be correlated to the elite players' positions on the national ranking for men's singles, which might be taken into account when designing training programs. The test may be used to provide a benchmark for players in relation to the physical performance level and may be a useful tool in evaluating longitudinal changes in conditioning e.g., seasonal variations. However, the present B-ENDURANCE test is focused on single badminton, and from a practical perspective, we suggest that physiologists and coaches use the B-ENDURANCE test to evaluate single players' on-court badminton-specific endurance capacities.
The authors are grateful to the Danish Badminton Association and Stenhus Badminton College for supporting this study. Furthermore, they express their appreciation to the Danish badminton national team players, the International Badminton Academy, Stenhus Badminton College, and all the other subjects for their participation in the study and to Larsen Elektronik for helping in constructing the sensors. At the time this study was conducted, the first author was a PhD student of the University of Copenhagen. However, the author received funding from Stenhus Gymnasium & HF (Stenhus Badminton College) to cover the salary. No other financial support has been provided for this project. The results of this study do not constitute endorsement of the product by the National Strength and Conditioning Association.
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