Resistance training may be undertaken to improve a number of different muscular force outcomes (11). Typically, these outcomes have been identified as maximal strength, hypertrophy of muscle, power, and strength-endurance (S-E), also known as local muscular endurance (11). Over the past few decades, the majority of studies have focused on the training or testing of maximal strength, power, and hypertrophy (1-5,8,12,13). Less research in comparison has looked at S-E, either in training methodologies aimed at improving it or in the development of appropriate and valid tests for assessing it (14). This may be due to the great difficulty that lies in choosing the appropriate resistance or exercise to assess this factor and the fact that the nature of S-E can vary between sports (e.g., rowing vs. wrestling) (14). For a set of resistance training to be considered as S-E “oriented,” the American College of Sports Medicine (ACSM) Position Stand concerning progression models in resistance training deems that it must consist of at least 10 progressing to 25+ repetitions (11). This may occur across a broad spectrum of resistances with more advanced trainers (11).
The aim of physical testing is to identify the physical performance characteristics associated with elite athlete performance and consequently identify whether athletes may improve their physical training to improve their sports performance. For example, testing of a broad range of athletes in a sport may indicate that higher ranked athletes tend to possess higher strength or power scores than less successful athletes, and therefore, lower level athletes may train to improve those aspects in an effort to improve sports performance. Accordingly, S-E testing may only be of value to sports where S-E is desirable in achieving a positive sports outcome. One such sport may be rugby league football, which is a collision sport played worldwide (9). In particular, due to the number of collisions with large opponents that occur during a game, S-E as manifested against heavy resistances is of interest. Previous studies have illustrated the importance of maximum strength and power in determining playing rank in rugby league (1-5,9,13) and American college football (8); however, S-E has not yet been included as an outcome measure.
The purpose of this study was to compare the 3 different measures of upper-body S-E to determine (a) if they could distinguish between professional rugby league players participating in the elite National First Division (NRL) from state-based second division (SRL) players (1,5,8) and (b) were valid measures of S-E as determined by the criteria set down by the ACSM Position Stand (11). In particular, the tests comprised 1 test of relative S-E and 2 tests of absolute S-E with markedly disparate resistances (11,14).
Experimental Approach to the Problem
Two different studies were performed in separate years on 2 different groups of professional rugby league players to distinguish the appropriateness and validity of 3 different tests of upper-body S-E. Conceptually, these tests assess 2 different theories of the measurement of S-E-that being relative S-E and absolute S-E (14). The investigated resistances also spanned a wide spectrum, which is considered to be an important factor in determining the relative importance of endurance activities (14). The bench press exercise was chosen because upper-body pushing and pressing away of opponents is a fundamental task in the sport. Previous research has shown that bench press strength and power tests discriminate athletes in rugby league (1-4)-whether absolute or relative S-E also did was of interest.
In the first study, 26 subjects (NRL = 13, SRL = 13), who were identified as possessing similar strength levels despite participating in differently ranked leagues, were tested for 1 repetition bench press (1RM BP) strength. Three days later, they were tested by having to perform as many bench press repetitions as possible until fatigue with a resistance of 60% 1RM BP (BP RTF 60% 1 repetition maximum [1RM]). A figure of 60% 1RM was chosen as considerable research indicates that around 20 or more repetitions can be performed at such a resistance (6,7,10,12), which would fulfill the ACSM Position Stand (11) concerning the validity of the test. This study would give rise to determining if more elite players could perform more work (repetitions) at the same relative intensity as less successful counterparts and consequently is considered a test of relative S-E (14).
In the second study, 38 subjects comprising 19 NRL and 19 SRL players were tested for 1RM BP strength. On 2 different days, they were tested by having to perform as many bench press repetitions as possible till fatigue with 2 markedly different resistances of 102.5 kg (BP RTF 102.5) and 60 kg (BP RTF 60). This study would give rise to determining if more elite players could perform more work (repetitions) at the same absolute resistance as less successful counterparts and consequently is considered a test of absolute S-E (14). The 2 absolute resistances chosen were a high-intensity resistance of 102.5 kg (i.e., the NFL 225 test) and a more moderate resistance of 60 kg. These markedly different resistances may distinguish differing S-E qualities-high-intensity S-E or low-intensity S-E (14)-it is unknown if either is more important for rugby league success.
The relationship between playing rank and physical performance data can be analyzed by assigning the groups a ranking of 2 for the NRL groups or 1 for the SRL groups. The individual scores in the various tests are then correlated to player group ranking to determine the extent of the relationship between playing rank and S-E score, a method that has been used before in this type of analysis (1-5).
For both studies, all subjects were members of the same football club and performed similar strength training, relative to their different playing positions, strength levels, and training experience in the 8 weeks leading up to testing. All subjects were experienced in resistance training, with a minimum of 3 years of participation. This included maximal strength, power, and S-E training. However, the full-time professional NRL players performed additional training sessions (fitness, skill, and tactics), but not additional resistance training. All the athletes had performed a preseason resistance training cycle immediately prior to testing, establishing them in peak condition at the time of testing. The subjects were informed of the purpose and nature of the tests and voluntarily consented to participate in the testing procedures.
Twenty-six subjects, who were identified from a much larger player pool as being of similar in maximum strength and recent training history but different in player ranking, volunteered to participate in this study, which was considered to be a normal part of their testing and training requirements. The 2 groups, comprising 13 NRL and 13 SRL players, are described as being 94.4 (7.9) kg and 87.8 (8.6) kg in mass, 182.4 (6.5) and 184.8 (6.4) cm in height, and 24.9 (3.0) and 20.0 (1.2) years of age, respectively. The groups were different in age and body mass but not height. There was no difference in 1RM BP strength between the groups (NRL = 125.0 ± 15.4, SRL = 120.0 ± 10.8).
Thirty-eight subjects, comprising 19 NRL and 19 SRL players, volunteered to participate in this study, which was considered to be a normal part of their testing and training requirements. They are described as being 97.4 (10.4) kg and 92.5 (7.5) kg in mass, 186.1 (5.4) and 184.0 (4.8) cm in height, and 25.0 (3.3) and 19.5 (1.7) years of age, respectively, of which only the age data were significantly different between the groups. The groups were also different in 1RM BP strength (NRL = 143.0 ± 15.6, SRL = 120.4 ± 12.2).
Athletes were assessed for 1RM BP strength using the methods previously outlined (1-4). Seventy-two hours later, after warming up with their usual procedures, they were required to perform a repetitions-to-fatigue test bench pressing a relative resistance equal to 60% of their individual 1RM BP (RTF BP 60% 1RM). This test was deemed a test of relative S-E and was implemented to determine if more successful athletes could perform more work at the same relative percentage intensity levels as similarly trained, although less successful counterparts. As no difference existed between the groups in 1RM BP strength, the 60% 1RM resistance was essentially the same for both groups.
Athletes were assessed for 1RM BP strength using the methods previously outlined (1-4). After a further 10-minute rest, the athletes were asked to perform a repetitions-to-fatigue test bench pressing an absolute resistance of 102.5 kg (RTF BP 102.5). This resistance was chosen because it is a widely used test in American football, where it is known as the NFL 225 BP test (7,12). Data suggest that while athletes at college level may average 7 repetitions with this resistance (7), the more successful athletes at the National Football League Draft Combine testing camp typically perform 20 to 21 repetitions (12). These data suggest that this test may distinguish between S-E capabilities of athletes within the same sport and that is why it was chosen.
The second test of absolute S-E was performed 72 hours later. After warming up with their usual procedures, the athletes were required to perform a bench press test of repetitions to fatigue with an absolute resistance of 60 kg (RTF BP 60). This lighter resistance was chosen to determine if a medium-intensity resistance (as opposed to the high-intensity resistance of 102.5 kg) was more effective in distinguishing NRL from SRL players (14). Furthermore, the validity and appropriateness of both absolute tests of S-E, according to the ACSM criteria (8), had yet to be determined for this population group.
Factorial analyses of variance were used to determine if differences existed between the groups in measures of BP RTF 60% 1RM, BP RTF 102.5, and BP RTF 60 as well as 1RM BP. In the event of a significant F ratio, Fisher post least squares difference (PLSD) post hoc comparisons were used to determine where these differences existed. Pearson moment correlations were also calculated between individual S-E scores and ranking as SRL or NRL level. Significance was accepted at an alpha level of p ≤ 0.05.
Results for study 1 concerning the merit of relative S-E testing are contained in Table 1. No difference existed between NRL and SRL groups in how many repetitions could be performed to fatigue with a relative resistance of 60% 1RM BP. Test scores in BP RTF 60% did not correlate significantly to player ranking and were of an extremely minor magnitude. Results for the 2 absolute tests of S-E are contained in Table 2. Both tests deemed to be measuring absolute S-E, which were effective in distinguishing NRL from SRL players. The significant correlation between BP RTF 102.5 and playing rank was moderate (r = 0.63, r2 = 0.4) and almost identical to that for maximum strength (r = 0.64, r2 = 0.41), but higher than that for the BP RTF 60 test (r = 0.54, r2 = 0.29).
The results of this investigation illustrate that the tests deemed to be tests of absolute measure of S-E significantly discriminate between rugby league players of different grades or achievement levels, despite those players possessing similar recent training experiences. However, a relative S-E test measuring the ability of players to perform work at the same relative intensity of 60% 1RM did not distinguish between players. The possible reasons for these results will be discussed below along with a discussion on the appropriateness and validity of these tests in assessing S-E in rugby league players.
As rugby league is a collision-based sport where players attempt to push away or drive opponents backward throughout the game, it would appear that a test entailing pushing or pressing resistance away from the body would meet the basic upper-body movement specifications at least for assessing S-E. Certainly, 1RM BP and maximum power (Pmax BT) during bench throw/pressing clearly distinguish NRL players from SRL and lower level players (1-4,13). Clearly, the choice of the movement was applicable for this sport and population group-it is more of a case of choosing the appropriate resistance and test methodology.
It could be expected that athletes with similar training backgrounds within a sport score similarly at the same relative % 1RM level in an S-E test. Many studies exist that illustrate that 20 to 21 repetitions are typically performed with resistances of around 60% 1RM in the bench press (and other exercises), as was the case in this study (6,7,10,13). If differences do exist between athletes in relative S-E, then conceivably they may be between athletes of markedly dissimilar sports, such as rowing and power lifting, and these differences, if they exist, may occur at low % 1RM levels. It is conceivable, e.g., that the training that rowers perform would afford them considerable advantage in buffering the high muscle acidity associated with the performance of >25 to 30 repetitions (performed @ <50% 1RM), resulting in them possessing an advantage over powerlifters who do not typically perform very high repetition training. It remains to be seen if this type of relative S-E testing could actually distinguish between similarly trained although differently ranked athletes within the same sport (e.g., higher and lower ranked rowers). The results of this investigation suggest not and as such tests of relative S-E are not recommended for use in distinguishing between athletes within a sport. Stone et al. (14) have stated that relative tests of endurance have little actual relevance to real-life situations.
Consequently, appropriate tests of absolute S-E have been sought. The great difficulty lies in choosing the appropriate resistance and methodology (e.g., 1-set S-E performance vs. multiple-set S-E performance). In this investigation, only a 1-set methodology was used and the discussion will be limited to results from this type of methodology; however, future research may also need to look at multiple-set S-E testing methods to determine if they garner more distinguishing results between athletes of different ranking within a sport.
On the surface, the BP RTF 102.5 test appears quite successful in distinguishing NRL from SRL players. However, on further investigation, it would also appear invalid as a test of S-E, according to the ACSM criteria (11). The ACSM guidelines require S-E sets to have a minimum of 10 repetitions. For the SRL group, only 4 of the 19 subjects could perform 10 or more repetitions with this resistance and 3 could not even perform 1 repetition. In the NRL group, 4 athletes could not perform 10 repetitions with this resistance. Consequently, the resistance of 102.5 kg must be considered too heavy to represent a test of S-E per the ACSM guidelines (11) for half of the subjects. Clearly, this test represented a feat of maximal or near-maximal strength for the majority of those subjects. So, while there was a significant difference between groups in the performance of this test, it would be unwise to state that based on this test alone absolute S-E is a potent discriminator of rugby league player ranking, given that BP RTF 102.5 test was not measuring S-E in a large section of this population.
The results of the BP RTF 60 test were also significantly different between the groups; however, the high number of repetitions performed by all subjects in both groups suggests that this test may be a more valid test, according to the ACSM criteria, of measuring S-E for this population group. Based on the results of the BP RTF 60 test, it could be more confidently stated that absolute S-E does distinguish between rugby league players of different achievement levels. As rugby league is a game where absolute work is important-large opposing players must be driven backward-it could be expected that an appropriate test would indicate the importance of absolute S-E in distinguishing between players of different caliber. As the results for the relative S-E test indicate that differently ranked players of the same maximal strength levels do not possess greater relative S-E abilities, the reasons for the results in study 2 must be attributed to differences in absolute or maximal strength levels.
The overwhelming body of data clearly illustrates that rugby league players participating in higher levels of competition possess higher maximal strength levels compared with participants in lower ranked competitions, despite no or sometimes minor differences in body mass (1-5,13). The superior maximal strength capabilities extend to greater absolute S-E capabilities and the ability to perform more work at the absolute submaximal resistances, in this case ranging from 60 to 102.5 kg. Higher absolute 1RM BP levels would mean that for the NRL players, the absolute resistances of 60 and 102.5 kg would be at lower percentages of the 1RM compared with the SRL players. Given the results for study 1 and various other studies (6,7,10) that have investigated repetition performance levels at submaximal resistances, it is to be clearly expected that the much stronger group would perform more repetitions with resistances equivalent to lower % 1RM levels. Thus, the significant differences that existed between the groups in study 2 may be attributed to the advantage that higher levels of maximal strength afford one group over another when the S-E test is based on absolute work performance.
So, while absolute S-E scores correlated well with player ranking in study 2, these results appear predicted upon the fact that maximal strength relates most highly to rugby league player ranking. In study 2, the correlation between player ranking and 1RM BP was of a similar magnitude to those in previous studies (1-4). The 2 absolute resistance tests also correlated well to 1RM BP scores (r = 0.94, r2 = 0.88 for BP RTF 102.5 and r = 0.82, r2 = 0.67 for BP RTF 60), although as already discussed, the higher 102.5 kg resistance test is most likely a test of near-maximal strength, not S-E, and consequently could be expected to correlate well to a maximal strength test. Nonetheless, a resistance of 60 kg represented a mean relative resistance of only 42 and 50% 1RM for the NRL and SRL groups, respectively, but performance at this low intensity still appears statistically largely accountable on 1RM strength levels (r2 = 0.68).
Based on these results and those of other studies (6,7,10,12), it would indicate that absolute S-E is largely dependent upon maximal strength, and therefore, efforts should be made to improve maximal strength levels as this will largely attribute to increases in absolute S-E capabilities. It must also be stated that only a 1-set model of assessing S-E was used in these studies, and it is not known if a multiple-set protocol would garner different results.
Athletes with similar training backgrounds within a sport score similarly at the same relative % 1RM level in an S-E test, and consequently, relative S-E tests are not recommended for distinguishing between athletes within a sport. Conceivably relative S-E tests may distinguish between athletes of markedly dissimilar sports and hence may be useful more in a multisport talent identification program.
Tests of absolute S-E appear better able to distinguish between higher and lower ranked athletes within a sport. The greatest difficulty may lie in choosing the appropriate resistance. Based on these studies and the ACSM guidelines, the absolute resistance chosen should allow the worst performed athletes to lift 10 to 20 repetitions, with a group average in the range of 30 to 40 repetitions and with the better-performed athletes performing up to 60+ repetitions. For experienced professional rugby league players, an absolute resistance of 60 kg appears to be an appropriate absolute resistance that measures S-E capabilities and distinguishes playing rank. Athletes in other sports should choose an absolute resistance of magnitude commensurate with their absolute strength levels that allows for the above repetition achievements.
Furthermore, the results of this and other studies indicate that absolute S-E is largely dependent upon maximal strength, and therefore, efforts should be made to improve maximal strength levels as this will largely attribute to increases in absolute S-E capabilities.
1. Baker, D. Comparison of maximum upper body strength and power between professional and college-aged rugby league football players. J Strength Cond Res
15: 30-35, 2001.
2. Baker, D. The effects of an in-season of concurrent training on the maintenance of maximal strength and power in professional and college-aged rugby league players. J Strength Cond Res
15: 172-177, 2001.
3. Baker, D. A series of studies on the training of high intensity muscle power in rugby league football players. J Strength Cond Res
15: 198-209, 2001.
4. Baker, D. Differences in strength and power between junior-high, senior-high, college-aged and elite professional rugby league players. J Strength Cond Res
16: 581-585, 2002.
5. Baker, D and Newton, RU. Comparison of lower body strength, power, acceleration, speed and agility and sprint momentum to describe and compare playing rank in professional rugby league players. J Strength Cond Res
22: 153-158, 2008.
6. Brzycki, M. Strength testing
: Predicting a one-rep max from reps-to-fatigue. J Health Phys Educ Rec Dance
64: 88-90, 1993.
7. Chapman, PP, Whitehead, JR, and Binkert, RH. The 225-lb reps-to-fatigue test as a submaximal estimate of 1-RM bench press
performance in college football players. J Strength Cond Res
12: 258-261, 1998.
8. Fry, AC and Kraemer, WJ. Physical performance characteristics of American collegiate football players. J Strength Cond Res
5: 126-138, 1991.
9. Gabbet, TJ. Science of rugby league football: A review. J Sports Sci
23: 961-976, 2005.
10. Hoeger, W, Hopkins, D, Barette, S, and Hale, D. Relationship between repetitions and selected percentages of one repetition maximum: A comparison between untrained and trained males and females. J Appl Sport Sci Res
4: 47-54, 1990.
11. Kramer, WJ, Adams, K, Carafelli, E, Dudley, GA, Dooly, C, Feigenbaum, MS, Fleck, SJ, Franklin, B, Fry, AC, Hoffman, JR, Newton, RU, Potteiger, J, Stone, MH, Ratamess, NA, and Triplett-McBride, T. American College of Sports Medicine Position Stand: Progression models in resistance training for healthy adults. Med Sci Sports Exerc
34: 364-380, 2002.
12. McGee, KM and Burkett, LN. The National Football League Combine: A reliable predictor of draft status? J Strength Cond Res
17: 6-11, 2003.
13. Meir, R, Newton, R, Curtis, E, Fardell, M, and Butler, B. Physical fitness qualities of professional rugby league football players: Determination of positional differences. J Strength Cond Res
15: 450-458, 2001.
14. Stone, MH, Stone, ME, Sands, WA, Pierce, KP, Newton, RU, Haff, GG, and Carlock, J. Maximum strength and strength training-A relationship to endurance? Strength Cond J
28: 44-53, 2006.