Rugby union or rugby is a popular contact sport involving 2 teams of 15 players. Each team is made up of 2 distinct playing units, with forwards (i.e., all players involved in the scrum, 8 per team) primarily considered the “ball winners” and backs (i.e., all players not involved in the scrum, 7 per team) considered the “ball carriers” (16). The positional demands of rugby necessitate different force-generating or neuromuscular abilities. For example, front row forwards require strength and power to gain ball possession, with loose forwards requiring similar attributes to gain and retain ball possession (16). High speed is important for the halfback to accelerate away from defenders, with midfield backs requiring strength, speed, and power because of a high frequency of contact with other players (16). Despite these observations, there is a paucity of data examining the neuromuscular performance of elite rugby players. Such an analysis has important implications for defining positional needs and assessment, exercise prescription, and monitoring training and recovery.
Elite rugby union players have unique physical characteristics, with forwards being taller and heavier and possessing greater body fat than backs (8,20,24,27,31). To account for body size differences, it is common practice to normalize performance by dividing the outcome variable by body mass, also known as isometric scaling. This approach has been criticized (1,21) because it assumes a linear relationship between body size and performance and fails to account for differences in lean, fat, and total mass. Allometric scaling has been proposed as a more effective method for normalizing performance by expressing data raised to a body size exponent (e.g., two-thirds scale for power and strength) based on the theory of geometric symmetry (21). Taking this approach with the analysis of rugby union data would therefore provide a better understanding of the neuromuscular performance of elite forwards and backs.
Testosterone and cortisol are potent hormones contributing to long-term changes in muscle growth and consequential performance (11,35). It has been suggested that endogenous hormones might also contribute to short-term neuromuscular performance during power events (35). For instance, studies involving male athletes (e.g., weightlifters, soccer and handball players, sprinters) have reported low to moderate correlations between testosterone and/or cortisol concentrations, measured in blood or saliva, and jump height, sprint ability, and maximal strength (6,7,22,29). Accordingly, for trained males, the performance of speed, power, and strength might be related to hormone secretion patterns. To our knowledge, there is no such research on elite rugby union players, nor are there any data comparing positional groups in different sports.
This study compared the neuromuscular performance (speed, power, and strength) of elite rugby union forwards and backs. Based on the literature, it was hypothesized that the backs would demonstrate greater speed and the forwards would demonstrate greater absolute power and strength but that no differences in power would remain once these variables were normalized for body mass (in kg0.67). Relationships between player performance and salivary hormones were also examined. Given previous findings, we hypothesized that the salivary hormone concentrations of players would correlate to speed, power, and strength.
Experimental Approach to the Problem
To compare the neuromuscular performance of elite rugby forwards and backs, various measures of speed (10-m, 20-m, or 30-m sprints), power (70-kg squat jump-SJ, 50-kg bench press throw-BT), and strength (box squat-BS, bench press-BP) were assessed on different days. These are common tests of neuromuscular performance and relevant to the physical demands of rugby union. Saliva samples were collected immediately before each test and assayed for testosterone (Sal-T) and cortisol (Sal-C). The Sal-T to Sal-C ratio (Sal-T/C) was also calculated and used for analysis. Saliva is a noninvasive and compliant medium for determining the biologically active “free” hormone (18,19). Correlations were used to assess the relationship between the hormonal and performance variables.
Thirty-four professional male rugby union players were recruited for this study. They were training for the Super 14 rugby competition, the major event in the southern hemisphere comprising teams from New Zealand, South Africa, and Australia. The following assessment procedures occurred over the course of 10 days before the start of the Super 14 competition, ensuring players were in peak physical condition. Players were currently performing intensive training 5 days a week, involving speed development, power and strength conditioning, and endurance exercise and sports-specific skill work. Each subject had the risks of the investigation explained to them and signed an informed consent prior to this study. The Human Subject Ethics Committee of the Waikato Institute of Technology provided ethical approval.
The assessment procedures for speed, power, and strength are similar to those described elsewhere (2,10,12,14). Subjects were familiar with each test as part of their training and ongoing assessment throughout the season. To account for diurnal variation, subjects were assessed at the same time of day (9 am ± 1 hour) following a standard warm-up, with each test separated by 2 to 3 days. Because of injuries and other training objectives, some subjects were unable to complete the entire test battery.
Body Composition Assessment
Body composition was assessed on the first day of the study using a stadiometer (SECA 220, Birmingham, England) and electronic scales (SECA 702, Birmingham, England), with players wearing socks, shorts, and a training shirt only. Skinfold measurements were collected at 7 sites (i.e., triceps, subscapular, biceps, supraspinal, abdominal, front thigh, calf) with a pair of Harpenden skinfold calipers (British Indicators, England) by anthropometrists accredited with the International Society for the Advancement of Kinanthropometry. Percent body fat was calculated from these data (36). The physical characteristics of subjects are provided in Table 1.
Running speed was assessed on a flat outdoor surface using an electronic timing system (Swift Performance Equipment, Australia). This system has a dual-beam modulated visible RED light system with polarizing filters recording sprint times to 0.01 seconds (s). Subjects started in a crouched position, with both feet placed a short distance (0.5 m) behind the start line, before sprinting through a series of timing lights placed at 10-m, 20-m, or 30-m from the first set. Timing commenced as the first electronic beam was broken. Based on the time motion analysis of sprints during rugby competition (17), the maximum distances for the sprints were 20-m (forwards) and 30-m (backs), with the 10-m and 20-m split times recorded for both positional groups. Three trials were performed with each players' best time used for analysis. The reliability of sprint measures, as a coefficient of variation (CV), are high (1.9-2.0%) (10). Average running velocities (m·s−1) were also calculated.
Power was assessed using a Smith machine and free weights (Fitness Works, New Zealand). The SJ required subjects to start in a standing position with a 70-kg load on the shoulders. Subjects then squatted to a self-selected depth before explosively jumping in the concentric phase to achieve maximal height (12). On landing, subjects were instructed to bend the knees to better absorb the impact forces. For the BT, subjects lay supine on a bench and lowered a 50-kg load to touch their chest before explosively throwing the load in the concentric phase. On descent, the bar was caught and lowered with the assistance of spotters. Mean (MP) and peak (PP) power were calculated for the concentric phase of the SJ and BT using the GymAware system (Kinetic Performance Technology, Australia). This system consists of a linear encoder, attached to the bar via a retractable cord, and provides valid (r ≥ 0.97) power measurements for these and similar lifts (14). The reliability of the power measures, tested in our laboratory, was high (CV 2.0 to 2.5%). As recommended (15), SJ power was calculated from the combined mass of the load and participant (i.e., system power), with BT power derived from the load mass only. For both exercises, 3 sets of 4 repetitions were performed to ensure maximal power was maintained (14), with the best trial across these sets used for analysis.
Strength was assessed using a squat rack and bench, an Olympic barbell, and free weights (Fitness Works, New Zealand). Preparation for the BS began with subjects in a standing position, with the loaded bar on the shoulders. Subjects then descended until the thigh was parallel to the ground, using a weighted box at this position, before extending upward to the start without assistance. Box height was adjusted to account for subject differences in limb length. The BP began with subjects laid supine on a bench with arms fully extended, with the loaded bar then lowered to the chest before pressing to full extension without assistance. For safety reasons, both exercises were performed until a 2 to 4 repetition maximum (RM) lift was achieved across 4 to 5 sets, with the 1RM lift estimated from these data (23). These strength measures are highly reliable with CVs of 1.5 to 2.3% (10). To account for body size differences, the power and strength data were also normalized for analysis by first raising body mass (in kg) to the power of 0.67 (21). The performance of rapid limb movements (e.g., sprinting) does not require scaling for body size (21).
For each test, a 2-mL saliva sample was collected before the maximal lift or trial to account for hormonal changes resulting from the warm-up procedures. Sugar-free gum (Extra brand peppermint flavor, Wrigley's, New Zealand) was used to increase saliva flow, with saliva samples stored at -80°C before assay. Saliva was assayed for testosterone and cortisol using diagnostic kits (Diagnostic Systems Laboratories or DSL, USA) and modified radioimmunoassay methods (19,26). Briefly, standards from DSL kits were diluted in phosphate-buffered saline (PBS) to cover the concentration range of 0 to 500 pg/mL−1 for Sal-T and 0 to 51.2 ng/mL−1 for Sal-C. The DSL standards were also diluted in PBS to obtain low and high values for each assay with the antibodies diluted in a PBS solution containing 0.05% bovine serum albumin. Low- and high-quality control samples were also assessed. Testosterone assay sensitivity was 1 pg/mL−1 with intraassay and interassay CVs for the control samples of <7% and <8%, respectively. Cortisol assay sensitivity was 0.05 ng/mL−1 with respective intraassay and interassay CVs of <10% and <9%. Samples for each participant were analyzed in the same assay to eliminate interassay variance.
Means and SD were calculated for the dependent variables. The neuromuscular and hormonal variables were compared by positional group (forwards vs. backs) using independent t-tests. Relationships between the neuromuscular and hormonal variables were examined as a collective group (squad) and by positional group using Pearson product moment correlation coefficients (r). Data not meeting statistical assumptions were log transformed before analysis. Log transformed data are presented back-transformed in their original units. The criterion level for significance was set at p ≤ 0.05.
The forwards were taller and heavier and possessed a higher percentage of body fat than the backs (p < 0.01 to 0.001, Table 1). In terms of running speed (Table 2), the backs demonstrated faster times and greater velocities for the 10-m and 20-m sprints (p < 0.01 to 0.001). The power results are shown in Table 3. The forwards produced greater SJ PP and MP (p < 0.05 to 0.001), but these differences were not apparent when normalized for body mass (p > 0.05). Similarly, BT MP was greater in the forwards (p < 0.05), but normalizing performance removed these differences (p > 0.05). However, BT PP revealed no differences between forwards and backs either before, or after, normalization (p > 0.05). In terms of strength (Table 4), the forwards demonstrated a greater BS 1RM (p < 0.01), but their mass-corrected lift did not differ from the backs (p > 0.05). Conversely, the absolute and normalized BP 1RM lifts were both superior in the forwards (p < 0.05 to 0.001).
The Sal-T and Sal-C concentrations of the forwards and backs did not differ on any test occasion (p > 0.05, Table 5). The Sal-T/C ratio was also consistent for both positional groups during testing, except on the speed day, when it was significantly higher in the backs (p < 0.05). Salivary hormones correlated to various speed measures (Table 6). Squad data revealed a significant correlation between Sal-T and the 10-m (r = −0.48, p < 0.05) and 20-m (r = −0.56, p < 0.01) times and accompanying velocities (r = 0.48 to 0.61, p < 0.01 to 0.05). The Sal-T/C ratio for the squad also correlated to the 20-m times (r = −0.43) and the 20-m (r = 0.43) and 10- to 20-m velocities (r = 0.46) (all p < 0.05). However, when analyzed by positional group, significant results were only found in the backs, with Sal-T correlating to the 10 to 20-m, 10 to 30-m, and 20 to 30-m velocities (r = 0.65, p < 0.05).
Hormone relationships with SJ power were also identified, with the Sal-C concentrations of the squad correlating to SJ MP (r = 0.41, p < 0.05). Normalized SJ MP also correlated to Sal-C for the squad (r = 0.41, p < 0.05), but only the cortisol data for the backs were significant after positional examination (r = 0.61, p < 0.05, Figure 1). Further relationships were identified between the Sal-T/C ratio for the squad and backs, respectively, and SJ MP (r = −0.39, p = 0.05) and MP·kg0.67 (r = −0.65, p < 0.05). For the BT, significant squad correlations were demonstrated between the Sal-T/C ratio and PP (r = 0.41, p = 0.05) and PP·kg0.67 (r = 0.43, p < 0.05). Significant results were only found in the backs following positional analysis, with the Sal-T/C ratio correlating to BT PP (r = 0.58, p < 0.05).
Additional correlations were demonstrated between salivary hormones and BS strength. As a squad, Sal-C correlated to BS 1RM·kg0.67 (r = 0.39, p = 0.05), but this relationship was only maintained in the backs once positional groups were examined (r = 0.69, p < 0.05, Figure 2). The Sal-T/C ratio for the squad also correlated to the BS 1RM (r = −0.42) and 1RM·kg0.67 lifts (r = −0.40), with these correlations remaining only in the backs after positional analysis (r = −0.62 to −0.73) (all p < 0.05 to 0.01). No hormonal relationships were found for the BP exercise, either as a squad or by positional group (p > 0.05).
The smaller backs demonstrated greater sprinting speed than the larger forwards. The larger body size of the forwards (vs. backs) may explain their superior performance in SJ PP and MP, BS strength, and BT MP. The performance of BT PP and BS strength were less dependent on the body size of players. The Sal-T and/or Sal-C concentrations of players (squad and backs) correlated to various speed, power, and strength measures to confirm relationships between neuromuscular performance and hormone secretion patterns.
The backs demonstrated superior sprinting speed than the forwards, in agreement with other research (8,9,17,20,27). High speed is important for halfbacks to accelerate away from defenders, with outside backs requiring considerable speed to out-maneuver their opponents, chasing kicks and covering in defence (16). Subsequently, player position is likely to depend, to some extent, on the genetic makeup of an individual (e.g., % fast-twitch muscle fibers, muscle fascicle length). However, there is limited information on the muscle fiber characteristics of elite rugby players. The conditioning of backs for rugby is also likely to emphasize speed development (17), further contributing to these performance differences. The combination of speed (velocity) and body mass does, however, lead to greater momentum among forwards than backs during sprinting (30). Momentum has a definite advantage in rugby, especially in body contact situations such as tackles and play associated with scrums, rucks, and mauls (30). Accordingly, achieving the optimal balance between size and speed would seem crucial for meeting the position-specific demands of this sport.
The greater absolute SJ power and BS 1RM strength of the forwards (vs. backs) may be explained by their larger body mass, based on the similarities in their normalized performances. It may be reasoned that the absolute expression of leg power and strength is important for contact situations in rugby (e.g., scrums, rucks, mauls), to predispose larger individuals to this positional group. Data concerning the leg power of elite rugby players are equivocal, with some reports favoring backs (8,9,25,34) or forwards (9,24,25,34), whereas others have found no positional differences (9,24,33). The wide range of assessments and data collection and analysis methods used may explain these discrepancies. Unfortunately, few studies have normalized the leg power of rugby players to account for body size differences (24,34), with these comparisons still limited by the use of isometric scaling, thereby penalizing heavier individuals (1). Given the limitations of isometric scaling, it has been proposed that investigations involving rugby players present performance results using power function ratios (i.e., allometric scaling) (16).
Similar to our BS 1RM findings, international forwards produced greater force (strength) than backs at low velocities during isokinetic half squats (25). Another study assessed the isoinertial leg strength of international players using horizontal and vertical squats (9). The horizontal lifts for the forwards (∼250-280 kg) exceeded the backs (∼215 kg), probably because of the movement-specific patterns of rugby (e.g., scrums), but their vertical squat lifts (∼120-125 kg and ∼118 kg) were not statistically different. It is noticeable that the squat values in this 1992 report are considerably less than our BS results (206 kg and 171 kg). Changes in rugby player size may explain this difference, with the body mass of elite forwards and backs (inclusive of the current results) increasing from the 1990s (91-105 kg, 78-83 kg) to the 2000s (104-111 kg, 85-93 kg), respectively (8,17,20,27,31,33). This trend is likely a result of the professional era of rugby and the popularization of resistance training, leading to a migration toward more mesomorphic somatotypes among rugby players (28). The divergence in strength might also be attributed to improvements in relative force production (i.e., force per unit of mass), resulting from more advanced training practices. Consequently, performance data collected from studies prior to rugby turning professional in 1995 may have little relevance to professional players and rugby today.
Of interest, the BS lifts for the squad in this study (191 kg and 8.64 kg0.67) are comparable to the squat performance of professional rugby league players (193 kg and 8.94 kg0.67), estimated from their 3RM lifts (12). Mean power developed by these rugby league players during a 30-kg SJ (2,200 W, 98 W·kg0.67) revealed further similarities to our squad results for the SJ exercise (2,394 W, 108 W·kg0.67), as did their 30-m sprint times (3.9-4.1 s) when compared to the 30-m times for the elite backs in this study (4.1 s). Because the neuromuscular performance of the elite rugby players in the present study is similar to that reported in the literature for elite rugby league players, coaches and conditioners working with rugby union teams may be able to utilize performance data obtained from the sport of rugby league.
The absolute and normalized BP 1RM strength of the forwards exceeded the backs. This finding is not unexpected because upper-body strength in general, and back, shoulder, and neck strength in particular, are thought necessary for this position (3). The larger mass of the forwards, combined with training to enhance the strength qualities of these muscle groups, offers a plausible explanation for our findings. Although BT MP followed a similar trend (i.e., larger forwards = greater performance), no differences in BT PP were found before or after normalization. Thus, in contrast to the lower body, no discernible patterns are evident between the upper-body strength and power characteristics of elite rugby backs and forwards. In a hierarchical relationship, a strong correlation should exist between strength and power exercises with similar movement patterns. However, research in rugby league players indicated that, although strength and power tests are related, with a shared variance of 35 to 80%, a large degree of unexplained variance (i.e., 20 to 65%) still exists (2). In other words, the transfer of neuromuscular effects from 1 exercise to another may be limited, possibly as a result of mechanical, neural, and/or structural differences (2). Collating data to make generic comparisons between forwards and backs might also mask differences, or similarities, that could exist within positional subgroups (e.g., inside vs. outside backs, loose vs. tight forwards). Sport-specific comparisons in the upper body are limited by a lack of research.
The salivary hormone concentrations of the elite rugby players correlated to various measures of speed, power, and strength to confirm the previous findings of studies involving trained male populations (6,7,22,29). These data suggests that, for trained individuals, differences in hormone secretion patterns might also explain the observed differences in the performance of the neuromuscular system. Although the exact mechanisms have yet to be determined, the short-term effect of testosterone and cortisol on the neuromuscular system could involve the modulation of the central (5) and peripheral neural networks (4,13) that initiate and control human movement. Energy metabolism offers a further mechanism to explain the hormonal effect. As a glucocorticoid, the primary role of cortisol is to stimulate gluconeogenesis and glycogenolysis via glycogen, protein, and lipid metabolism and through its permissive actions on other hormones (e.g., catecholamines and glucagon) (32). Collectively, these results provide support to the notion that endogenous hormones contribute to short-term neuromuscular performance during power events (35).
The relationships with speed and BT power are consistent with research examining blood total hormones (6,7,22) and suggest that individuals possessing a more anabolic environment (e.g., high testosterone and/or low cortisol) are likely to exhibit a superior performance. In contrast, the SJ power and BS strength relationships tended to favor individuals with a more catabolic environment (e.g., high cortisol and/or low testosterone). A similar relationship was observed among male weightlifters, with Sal-C positively related to their weight-corrected Olympic lifts in a competition (29). Considering the hormonal mechanisms, the direction of these relationships may depend on central and peripheral neural drive, the amount and type of muscle mass activated, and the energy requirements of the performance test. For athletes, the effect of training and/or competition on basal hormone secretion presents other complex possibilities (10,22). Methodological differences do make comparisons difficult. Saliva, as an indirect marker of the free hormone, provides a more sensitive endocrine measure than the total hormone (18). In our study, saliva samples were also collected immediately before each test, whereas previous research sampled (blood or saliva) subjects before the warm-up and assessment procedures (6,7,22,29). Nonetheless, one must remain cognizant of the limitations of research that compares only discrete hormone and performance values, regardless of the media used and the time of collection.
Unique to the literature, the relationships in this study showed signs of positional specificity (i.e., only backs). In fact, the results for the backs also appeared to drive the squad results. The hormone-performance relationships identified for starters and nonstarters in a professional soccer team partly corroborate our findings (22). That is, the blood (total) measurement of testosterone and/or cortisol in the starters and nonstarters were found to be related to speed, power, or strength across the playing season but never for the same hormone and performance test. In addition, the relationships for the starters were mostly derived from testosterone, whereas cortisol was more important for the nonstarters. Positional group differences may arise from genetic and/or training variation relating to muscle fiber distribution (6); muscle sensitivity to hormones (7); basal hormone secretion (7,22); and, in the case of the previous study (22), the amount of game time. Even so, the shared variance between the outcome variables indicates that the salivary hormone concentrations of the backs may still only explain 34 to 53% of the individual differences in performance. The similarities in the hormone concentrations of the forwards and backs add to the difficulty with interpretation. Further insight regarding the hormonal contribution to neuromuscular performance may be achieved through the long-term monitoring of hormones and experimental research within the rugby union paradigm (i.e., assessment, training, and competition).
In summary, the assessment of elite rugby forwards and backs revealed differences and similarities in speed, power, and strength, which can be attributed to genetic and/or training factors relating to the positional demands of rugby. The salivary hormone concentrations of players correlated to various speed, power, and strength measures, especially the backs, to confirm relationships between neuromuscular performance and hormone secretion patterns.
The present findings suggest that the expression of lower-body power and strength, and upper-body MP, are related to the body size of elite rugby players. Consequently, training to increase whole-body mass may also facilitate general improvements in these performance parameters. Training to increase muscle mass would seem particularly important by increasing the functionality of the mass changes and because of the greater density of muscle than other tissue (e.g., body fat). Conversely, a more functional approach to training may be necessary for improving lower-body speed and upper-body strength in elite rugby players. By default, the assessment of sprinting speed and BP strength may also provide the best measures for distinguishing between rugby forwards and backs at the elite level.
If the testosterone and/or cortisol concentrations of athletes contributed to the short-term expression of speed, power, and strength, then the acute and chronic monitoring of these hormones would seem important for establishing between- and within-individual normative data. Such an analysis may also help identify those individuals likely to respond more to changes in the hormonal environment. This information could benefit athlete performance and adaptation by enabling a more individualized approach to training prescription.
Funding support for this study was provided by The Horticulture and Food Research Institute of New Zealand.
1. Atkins, SJ. Normalizing expressions of strength in elite rugby league players. J Strength Cond Res
18: 53-58, 2004.
2. Baker, D and Nance, S. The relation between strength and power in professional rugby league players. J Strength Cond Res
13: 224-229, 1999.
3. Bell, W, Evans, WD, Cobner, DM, and Eston, RG. The regional placement of bone mineral mass, fat mass, and lean soft tissue mass in young adult rugby union players. Ergonomics
48: 1462-1472, 2005.
4. Blanco, CE, Zhan, W, Fang, Y, and Sieck, GC. Exogenous testosterone treatment decreases diaphragm neuromuscular transmission failure in male rats. J Appl Physiol
90: 850-856, 2001.
5. Bonifazi, M, Ginanneschi, F, Della Volpe, R, and Rossi, A. Effects of gonadal steroids on the input-output relationship of the corticospinal pathway in humans. Brain Res
1011: 187-194, 2004.
6. Bosco, C, Tihanyi, J, and Viru, A. Relationships between field fitness test and basal serum testosterone and cortisol levels in soccer players. Clin Physiol
16: 317-322, 1996.
7. Cardinale, M and Stone, MH. Is testosterone influencing explosive performance? J Strength Cond Res
20: 103-107, 2006.
8. Carlson, BR, Carter, JE, Patterson, P, Petti, K, Orfanos, SM, and Noffal, GJ. Physique and motor performance characteristics of US national rugby players. J Sports Sci
12: 403-412, 1994.
9. Cometti, G, Pousson, M, Bernardin, M, and Brullebaut, JL. Assessment of the strength qualities of an international rugby squad. In: 10th Symposium of the International Society of Biomechanics in Sports
. Rodano, R, Ferrigno, G, and Santambrogio, GC, eds. Italy, Edi Ermes, 1992. pp. 323-326.
10. Coutts, A, Reaburn, P, Piva, TJ, and Murphy, A. Changes in selected biomechanical, muscular strength, power, and endurance measures during deliberate overreaching and tapering in rugby league players. Int J Sports Med
28: 116-124, 2007.
11. Crewther, B, Keogh, J, Cronin, J, and Cook, C. Possible stimuli for strength and power adaptation: Acute hormonal responses. Sports Med
36: 215-238, 2006.
12. Cronin, JB and Hansen, KT. Strength and power predictors of sports speed. J Strength Cond Res
19: 349-357, 2005.
13. Dlouha, H and Vyskocil, F. The effect of cortisol on the excitability of the rat muscle
fibre membrane and neuromuscular transmission. Physiol Bohemoslov
28: 485-494, 1979.
14. Drinkwater, EJ, Galna, B, McKenna, MJ, Hunt, PH, and Pyne, DB. Validation of an optical encoder during free weight resistance movements and analysis of bench press sticking point power during fatigue. J Strength Cond Res
21: 510-517, 2007.
15. Dugan, EL, Doyle, TLA, Humphries, B, Hasson, CJ, and Newton, RU. Determining the optimal load for jump squats: A review of methods and calculations. J Strength Cond Res
18: 668-674, 2004.
16. Duthie, G, Pyne, D, and Hooper, S. Applied physiology and game analysis of rugby union. Sports Med
33: 973-991, 2003.
17. Duthie, G, Pyne, D, Marsh, DJ, and Hooper, SL. Sprint patterns in rugby union players during competition. J Strength Cond Res
20: 208-214, 2006.
18. Gozansky, WS, Lynn, JS, Laudenslager, ML, and Kohrt, WM. Salivary cortisol determined by enzyme immunoassay is preferable to serum total cortisol for assessment of dynamic hypothalamic-pituitary-adrenal axis activity. Clin Endocrinol
63: 336-341, 2005.
19. Granger, DA, Schwartz, EB, Booth, A, and Arentz, M. Salivary testosterone determination in studies of child health and development. Horm Behav
35: 18-27, 1999.
20. Holmyard, DJ and Hazeldine, RJ. Seasonal variations in the anthropometric and physiological characteristics of international rugby union players. In: Second World Congress of Science and Football
. Reilly, T, Clarys, J, and Stibbe, A, eds. Eindhoven, Netherlands, E & F.H Spon, 1991. pp. 21-26.
21. Jaric, S, Mirkov, D, and Markovic, G. Normalizing physical performance tests for body size: A proposal for standardization. J Strength Cond Res
19: 467-474, 2005.
22. Kraemer, WJ, French, DN, Paxton, N, Häkkinen, K, Volek, JS, Sebastianelli, WJ, Putukian, M, Newton, RU, Rubin, MR, Gomez, AL, Vescovi, J, Ratamess, NA, Fleck, SJ, Lynch, JM, and Knuttgen, HG. Changes in exercise performance and hormonal concentrations over a big ten soccer season in starters and nonstarters. J Strength Cond Res
18: 121-128, 2004.
23. Lander, J. Maximum based on reps. Nat Streng Cond Assn J
6: 60-61, 1985.
24. Maud, PJ and Shultz, BB. The US national rugby team: A physiological and anthropometric assessment. Physician Sportsmed
12: 86-99, 1984.
25. Miller, C, Quievre, J, Gajer, B, Thepaut-Mathieu, C, and Godemet, M. Characteristics of force/velocity relationships and mechanical power output in the French national rugby team and elite sprinters using ½ squats. In: Frontiers in Sport Science, the European perspective
. Marconnet, P, ed. Nice, France: European College of Sport Science, 1996. pp. 494-495.
26. Morelius, E, Nelson, N, and Theodorsson, E. Salivary cortisol and administration of concentrated oral glucose in newborn infants: Improved detection limit and smaller sample volumes without glucose interference. Scand J Clin Lab Invest
64: 113-118, 2004.
27. Nicholas, CW and Baker, JS. Anthropometric and physiological characteristics of first- and second-class rugby union players. J Sports Sci
13: 15, 1995.
28. Olds, T. The evolution of physique in male rugby union players in the twentieth century. J Sports Sci
19: 253-262, 2001.
29. Passelergue, P, Robert, A, and Lac, G. Salivary cortisol and testosterone variations during an official and a simulated weight-lifting competition. Int J Sports Med
16: 298-303, 1995.
30. Quarrie, KL, Handcock, P, Waller, AE, Chalmers, DJ, Toomey, MJ, and Wilson, BD. The New Zealand rugby injury and performance project. III. Anthropometric and physical performance characteristics of players. Brit J Sports Med
29: 263-270, 1995.
31. Scott, AC, Roe, N, Coats, AJ, and Piepoli, MF. Aerobic exercise physiology in a professional rugby union team. Int J Cardiol
87: 173-177, 2003.
32. Stewart, PM. The adrenal cortex. In: Williams Textbook of Endocrinology
. Larsen, RP, et al., eds. Philadelphia: WB Saunders, 2002. pp. 491-551.
33. Tong, RJ and Mayes, R. The effect of pre-season training on the physiological characteristics of international Rugby Union players. J Sports Sci
13: 507, 1995.
34. Vandewalle, H, Peres, G, Heller, J, Panel, J, and Monod, H. Force-velocity relationship and maximal power on a cycle ergometer. Eur J Appl Physiol Occup Physiol
56: 650-656, 1987.
35. Viru, A and Viru, M. Preconditioning of the performance in power events by endogenous testosterone: In memory of Professor Carmelo Bosco. J Strength Cond Res
19: 6-8, 2005.
36. Withers, RT, Craig, NP, Bourdon, PC, and Norton, KI. Relative body fat and anthropometric prediction of body density of male athletes. Eur J Appl Physiol Occup Physiol
56: 191-200, 1987.
Keywords:© 2009 National Strength and Conditioning Association
endocrine; muscle; field testing