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Changes in Strength, Power, and Steroid Hormones During a Professional Rugby Union Competition

Argus, Christos K1; Gill, Nicholas D1; Keogh, Justin WL1; Hopkins, Will G1; Beaven, C Martyn1,2

Journal of Strength and Conditioning Research: August 2009 - Volume 23 - Issue 5 - p 1583-1592
doi: 10.1519/JSC.0b013e3181a392d9
Original Research

Argus, CK, Gill, ND, Keogh, JWL, Hopkins, WG, and Beaven, CM. Changes in strength, power, and steroid hormones during a professional rugby union competition. J Strength Cond Res 23(5): 1583-1592, 2009-The purpose of this investigation was to assess changes in strength, power, and levels of testosterone and cortisol over a 13-week elite competitive rugby union season. Thirty-two professional rugby union athletes from a Super 14 rugby team (age, 24.4 ± 2.7 years; height, 184.7 ± 6.2 cm; mass, 104.0 ± 11.2 kg; mean ± SD) were assessed for upper-body and lower-body strength (bench press and box squat, respectively) and power (bench throw and jump squat, respectively) up to 5 times throughout the competitive season. Salivary testosterone and cortisol samples, along with ratings of perceived soreness and tiredness, were also obtained before each power assessment. An effect size of 0.2 was interpreted as the smallest worthwhile change. A small increase in lower-body strength was observed over the study period (8.5%; 90% confidence limits ±7.2%), whereas upper-body strength was maintained (−1.2%; ±2.7%). Decreases in lower-body power (−3.3%; ±5.5%) and upper-body power (−3.4; ±4.9%) were small and trivial. There were moderate increases in testosterone (54%; ±27%) and cortisol (97%; ±51%) over the competitive season, and the testosterone to cortisol ratio showed a small decline (22%; ±25%), whereas changes in perceived soreness and tiredness were trivial. Individual differences over the competitive season for all measures were mostly trivial or inestimable. Some small to moderate relationships were observed between strength and power; however, relationships between hormonal concentrations and performance were mainly trivial but unclear. Positive adaptation in strength and power may be primarily affected by cumulative training volume and stimulus over a competitive season. Greater than 2 resistance sessions per week may be needed to improve strength and power in elite rugby union athletes during a competitive season.

1Institute of Sport and Recreation Research New Zealand, AUT University, Auckland 1020, New Zealand; and 2Health and Food Group, HortResearch, Hamilton, New Zealand

Address correspondence to Christos K. Argus, argy15@hotmail.com.

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Introduction

Rugby union is a high contact, dynamic sport in which athletes require a combination of strength, power, speed, agility, endurance, and sport-specific attributes. As such, rugby union athletes perform concurrent training in an attempt to elicit gains in the many physical attributes required. Traditionally, concurrent training has been discussed as performing training modes with contrasting physical adaptations during the same training phase, typically strength and endurance (26). However, the term concurrent does not necessarily denote contrasting modes of training, rather concurrent is simply defined as existing or happening at the same time. Therefore, concurrent training may be more accurately discussed as numerous aspects of physical preparation targeted at the same time during a training phase. Indeed, team sport athletes predominately perform concurrent training to maximize adaptation in the many skill and physical aspects required. Similar to other athletes, physical conditioning plays a large role in the preparation and subsequent performance of rugby players.

Preseason conditioning is considered crucial for athletes to develop the physical characteristics required for successful competitive performance (e.g., strength, power, speed, aerobic, and anaerobic endurance) (35). Elite rugby athletes may sometimes train as many as 4 times per day during this phase of the season. During the competitive rugby season, the main emphasis of the conditioning program is to maintain gains made in strength, power, and lean body mass from preseason training (2). This can be difficult, however, as conditioning volume during the competitive season is reduced and additional training goals are introduced alongside previous training goals (i.e., additional training sessions such as position-specific drills).

It is unclear whether it is possible to maintain or improve preseason levels of physical performance throughout a competitive season that involves predominantly concurrent training. Indeed, research on other football codes has produced mixed findings (2,10,18,19,35). For example, Baker (2) found that bench press strength in college-aged rugby league athletes increased by 4.9%, whereas professional athletes maintained bench press strength (−1.2%) during a competitive season. Additionally, both upper-body and lower-body power were maintained in both of these playing groups (2). Gabbett (19) reported similar findings in that amateur junior rugby league athletes were able to maintain lower-body muscular power (−0.7%) throughout a competitive season. In contrast, Gabbett (18) found that nonelite, senior, club-level rugby league athletes had decreases in muscular lower-body power (−5.3%), whereas Schneider et al. (35) reported significant decreases in maximal upper-body strength (∼8%) and lower-body power (∼4.6%) in college-aged American football athletes throughout a competitive season.

Although there are similarities between these football codes (rugby union, rugby league, and American football), there are also many differences. For example, duration of work periods, type of work (dynamic or static), work to rest ratios, differences in the time spent at maximal and submaximal intensities, distances covered throughout the game, and different rules and regulations (9,13,20,30). These differences between codes and therefore training priorities may be partly responsible for the contrasting findings relating to the maintenance of strength and power previously reported in these football codes.

Another limitation of this literature is that there seems to be little research into the possible mechanisms contributing to the changes in strength and power across a competitive season of football. One such mediator might be the hormonal system. Testosterone and cortisol are steroid hormones with the testosterone to cortisol ratio (T:C ratio) reflecting the balance between anabolic and catabolic environments (16,17). Higher levels of testosterone have been previously linked to performance in strength and power tasks (7), whereas diminished levels of testosterone and increased levels of cortisol have been linked to overtraining and reduced performance (24,25,36). A better understanding of the effects of a competitive season on these steroid hormones and their relationship with strength and power may provide opportunity for enhanced programming strategies at an individual player level.

Although some evidence exists for the effect of the competitive season on the physical fitness characteristics of high-level rugby league and American football athletes, there is currently no such literature for elite rugby union athletes. Therefore, the primary purpose of this study was to investigate changes in strength, power, and levels of testosterone and cortisol over a 13-week competitive season of rugby union. It was hypothesized that strength and power would show little change over the course of the season. The secondary purpose was to identify the relationship between changes in strength and power and hormonal concentrations. It was hypothesized that there would be a relationship between strength, power, and hormonal concentrations.

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Methods

Experimental Approach to the Problem

After an intensive 7-week training phase (preseason), athletes were monitored for levels of strength, power, and salivary hormones throughout a 13-week competitive season of rugby union. Specifically, maximal upper-body strength (bench press, n = 32), lower-body strength (box squat, n = 20), upper-body power (bench throw, n = 29), and lower-body power (jump squat, n = 17) were assessed on separate occasions throughout the competitive season. On testing occasions when power was assessed, athletes also reported their perceptions of soreness and tiredness and provided saliva samples for testosterone and cortisol analyses (n = 32). Athletes were assessed on a minimum of 2 and up to 5 occasions during a 13-week international competition (weeks 1-2, 4-5, 6-7, 9-10, and 12-13) for each measure. The irregularity in time between testing occasions was due to national and international travel associated with the Super 14 competition. The discrepancy in number of testing occasions throughout the season was due to minor injuries that prevented an individual from performing the desired movements. Evenly spaced testing and/or equal numbers of tests per athlete are not requirements of the mixed modeling analytical procedure used in this investigation.

Although many physical attributes are required for successful performance in rugby union, only selected measures were monitored. This investigation was conducted using elite athletes in a professional environment, and therefore, the researchers were limited as to what and how often they were able to test athletes. The researchers did not have the ability to test athletes during on-field training sessions, where attributes such as endurance, agility, speed, and sport-specific skills were trained and where these parameters would have been most easily assessed. The researchers' access to athletes was during off-field training sessions, i.e., gym sessions, in which they were able to assess levels of strength and power at the start of certain sessions.

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Subjects

Thirty-two professional rugby union athletes from a Super 14 professional rugby team (age, 24.4 ± 2.7 years; height, 184.7 ± 6.2 cm; mass, 104.0 ± 11.2 kg) volunteered to take part in this study. The Super 14 competition is the premier provincial rugby competition in the southern hemisphere involving 14 full-time professional teams from 3 countries competing from February to May and involves national and international travel. Each athlete had at least 2 years of resistance training experience. Athletes were informed of the experimental risks and signed an informed consent document before the investigation. The investigation was approved by an Institutional Review Board for Use of Human Subjects (Auckland University of Technology Ethics Committee).

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Procedures

All strength (bench press or box squat) and power assessments (bench throw or jump squat) were performed at the beginning of the athlete's regular training session and were all performed on separate days. Athletes were given verbal encouragement throughout all assessments. All sessions were performed in the morning between 0800 and 1,000 hours. These 1 repetition maximum (1RM) measures derived from these exercises were selected due to their ability to accurately reflect levels of strength and power in both the upper body and lower body. Additionally, these exercises were regularly used as part of the athletes' training program, and therefore, the athletes were aptly familiarized.

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Strength (Bench Press and Box Squat)

Maximal strength was assessed using the bench press and box squat exercises. Each athlete was required to perform 3 sets (50, 70, and 90% effort, 2-6 repetitions [reps]) of submaximal bench press and box squat followed by 1 set to failure of 1-4 reps. Three-minute rest was allowed between each set. Each set to failure was used to predict the athletes' 1RM (27). For the bench press, athletes used a self-selected hand position and were required to lower the bar to approximately 90° angle at the elbows and then pressed the bar in a vertical movement so that the arms were fully extended. The depth and hand position were kept consistent throughout all testing occasions. During the box squat, athletes used a self-selected foot position and were required to lower themselves to a sitting position briefly on the box and then return to a standing position. The box height was adjusted for each athlete to allow the top of the thighs to be parallel to the floor while in the seated position. The foot position selected was kept consistent throughout all testing occasions. Each repetition was performed irrespective of time.

The following equation was used to predict bench press and box squat 1RM (27) and has been shown to have a correlation between actual and predicted 1RM of r = 0.993 and r = 0.969 for bench press and box squat, respectively (28):

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Soreness and Tiredness

On arrival at the training facility on the days when power was assessed, athletes rated their perceptions of soreness and tiredness on a 10-point scale ranging from 0 = normal to 10 = extremely sore (soreness scale) or 0 = normal to 10 = extremely tired (tiredness scale) (8).

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Salivary Hormones

Resting saliva samples were also obtained from each player before each power assessment. Salivary samples were obtained in this study because they are stress free and noninvasive (37). Salivary samples also reflect the free (nonprotein bound) plasma fraction that represents the biological activity of the steroid hormone (37), which has been reported to be more physiologically relevant than total blood levels (32,38). Athletes provided an ∼2 mL sample by passive drool into polyethylene tubes, which was stored at −20° C until assayed for testosterone and cortisol. Sugar-free gum was used to stimulate saliva flow before collection. The athletes then rested for 5 minutes before the beginning of the training session.

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Upper-Body Power (Bench Throw)

Upper-body power was monitored over the competitive season using a bench throw exercise performed in a Smith machine. Athletes warmed up with 2 sets of 4 reps of bench press at 50% of their most recent predicted 1RM bench press. Athletes then completed 2 sets of 4 reps of the bench throw at 50 and 60% 1RM bench press as these loads have been previously shown to produce maximal upper-body power in well-trained athletes (2). Athletes used a self-selected hand position and lowered the bar to a self-selected depth, which were kept constant throughout all testing occasions. Athletes were then asked to throw the bar vertically and explosively as possible, trying to propel the bar to a maximal height (31). A 3-minute rest was allowed between each set.

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Lower-Body Power (Jump Squat)

Lower-body power was monitored over the competitive season using a jump squat exercise performed in a Smith machine. Athletes warmed up with 2 sets of 4 reps lowering the bar to a 90° knee angle using a load of 55% of their most recent predicted 1RM box squat. Athletes then completed 2 sets of 4 reps of jump squat at 55 and 60% 1RM box squat as these loads have been previously shown to produce maximal lower-body power in well-trained athletes (2). Athletes used a self-selected foot position and lowered the bar to a self-selected depth, which were kept constant throughout all testing occasions. Athletes were then asked to jump as explosively as possible, to propel themselves and the bar off the ground. A 3-minute rest was allowed between each set.

The power produced during each bench throw and jump squat repetition was quantified with a Gymaware optical encoder (50-Hz sample period with no data smoothing or filtering; Kinetic Performance Technology, Canberra, Australia) using the methods described elsewhere (11). Quantification of the power produced during the jump squat exercise included body weight and bar mass (system mass) in the calculation, whereas only the bar mass was included for bench throw (12).

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Training Loads

Training loads for each session were recorded and calculated by randomly selecting 5 athletes to give the training session a rating of perceived exertion using the Borg scale (6). This intensity was then averaged and multiplied by the duration of the training (minutes) to calculate a training load for the session.

Before the beginning of the competitive season, athletes had completed 7 weeks of concurrent strength and conditioning. This entailed 3-7 resistance training sessions per week that differed between individuals (45-60 minutes; hypertrophy, 4 sets × 12RM, 90-second rest for 5 exercises; strength, 3-7 sets × 2-6RM, 3-minute rest for 4-6 exercises; power, 3 sets × 4-6 reps at 50-70% 1RM, 2-minute rest for 4-6 exercises; and circuit training, 6-12 reps, 30-second rest for 10 exercises). Conditioning consisted of 2-3 high-intensity running sessions each week (45-60 minutes; repeated efforts of 5- to 45-second duration, 1:2 work to rest ratio). Additionally, 1 or 2 recovery sessions were completed each week (30 minutes; swimming, cycling, and games). More than 50% of the athletes achieved or equaled personal bests in the box squat and/or bench press exercises during the preseason. Of the remaining athletes, many were nearing previous personal bests in the same exercises, suggesting a high degree of conditioning and training status among all the athletes.

During the 13-week in season, training was reduced to 1-3 resistance sessions (strength, 3-7 sets × 2-6RM, 3-minute rest for 4-6 exercises; power, 3 sets × 4-6 reps at 50-70% 1RM, 2-minute rest for 4-6 exercises), 1 or 2 high-intensity running sessions (20-30 minutes; repeated efforts of 5- to 20-second duration, 1:2 work to rest ratio), 3 or 4 skill/tactical team sessions, 1 or 2 recovery sessions, and 1 competitive match (played either internationally in South Africa or Australia or nationally in New Zealand) (Table 1).

Table 1

Table 1

Specifically, during the preseason, backs performed approximately 3.4 ± 1.3 resistance training sessions per week in comparison to 1.3 ± 0.6 resistance sessions per week during the in season. Forwards performed approximately 5.0 ± 1.7 resistance sessions per week in the preseason in comparison to 2.2 ± 0.7 resistance sessions during the in season. Resistance training loads and duration are presented in Table 2.

Table 2

Table 2

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Saliva Analysis

Saliva samples were analyzed in triplicate for testosterone and cortisol using radioimmunoassay methods (5). Briefly, standards from serum diagnostic kits (Diagnostic Systems Laboratories) were diluted in phosphate-buffered saline (Sigma P4417, Webster, TX) to cover the expected ranges of 0-18.56 and 0-1.73 nmol·L 1 for cortisol and testosterone, respectively. Saliva sample sizes of 50 and 100 μL were used for cortisol and testosterone, respectively. Antibodies were diluted with a phosphate-buffered saline solution containing 0.05% bovine serum albumin. Kit standards were diluted so that ∼50% binding was achieved with respect to the total counts. Detection limits for the assays were 0.4 and 0.004 nmol·L 1 for cortisol and testosterone, respectively.

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Statistical Analyses

The analysis was performed in 3 stages. First, the values of all measures were characterized via a straightforward reliability model, which consisted of a fixed effect for the mean value at each assessment and random effects to characterize typical variation within an athlete from assessment to assessment and between athletes in any one assessment (Table 3). Second, to show changes in mean values, a straight line was fitted to each athlete's values with assessment date as the predictor measure; the model provided the predicted change between the first and last assessment dates averaged over all athletes (Table 4). Finally, to investigate the ability of each measure to predict changes in performance, a similar model was used with each measure as the predictor measure (Table 5). All analyses were performed using the mixed procedure (Proc Mixed) in the SAS (Version 9.1; SAS Institute, Cary, NC).

Table 3

Table 3

Table 4

Table 4

Table 5

Table 5

Strength, power, and hormone concentrations were log transformed before all analyses; for these measures, the means shown are the back-transformed means of the log transform, whereas the SDs and effects (changes in means) are shown as percents. Soreness and tiredness were analyzed without transformation.

Standardized changes in the mean of each measure were used to assess magnitudes of effects by dividing the changes by the appropriate between-athlete SD. Standardized changes of <0.20, <0.60, <1.2, <2.0, and >2.0 were interpreted as trivial, small, moderate, large, and very large effects, respectively. To make inferences about true (large sample) value of an effect, the uncertainty in the effect was expressed as 90% confidence limits. The effect was deemed unclear if its confidence interval overlapped the thresholds for small positive and negative effects.

The interclass correlation and coefficient of variation (CV) for bench throw and jump squat activities were 0.900 and 5.0% and 0.904 and 4.8%, respectively. Validity of the Gymaware optical encoder has been previously reported elsewhere (11). The intra- and interassay CVs were 1.58 and 16.48% for cortisol and 1.61 and 12.75% for testosterone, respectively. The sample size for this investigation was limited to the number of athletes in the squad. All athletes in the squad were included, and therefore, no more athletes could be obtained.

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Results

Throughout the competitive season, the overall mean score for bench press and box squat 1RM strength was 141 and 194 kg, respectively (Table 3). A trivial decrease was observed in bench press strength (−1.7 kg), whereas a small increase in box squat strength (16.0 kg) was observed from the start to the end of the 13-week competitive season (Table 4).

Overall mean scores for bench throw and jump squat were 1,150 and 5,190 W, respectively (Table 3). A trivial decrease was observed in bench throw power (−40 W), whereas a small decrease in jump squat power (−175 W) occurred over the competitive season (Table 4).

The overall means for resting testosterone, cortisol, and the testosterone to cortisol ratio (T:C ratio) for the competitive season were 99 pg·mL−1, 2.0 ng·mL−1, and 50 (units), respectively (Table 3). Moderate increases in testosterone and cortisol were observed over the 13 weeks, whereas a small decrease occurred in the T:C ratio (Table 4). Trivial changes in ratings of perceived soreness and tiredness were also observed from the start to the end of the competition (Table 4). Individual differences over the competitive season were mostly trivial or inestimable and therefore not reported in Table 4.

The analysis of the relationship between predictor and dependent measures revealed mostly trivial but unclear findings (Table 5). However, some small to moderate relationships were observed. When examining relationships, one must note the large within (2) SDs necessary to allow for the performance enhancement in the dependent measure, e.g., to improve jump squat strength by 2.3% that an athlete would need to increase T:C ratio by 320%.

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Discussion

The primary purpose of this study was to investigate changes in strength, power, and levels of testosterone and cortisol over a 13-week competitive season in rugby union athletes. The present findings suggest that upper-body maximal strength and power of elite rugby athletes can be maintained throughout a competitive season. Interestingly, specific changes in the lower body were evident, with a small increase in maximal strength but a small decrease in power. Moderate increases in both testosterone and cortisol were observed throughout the competitive season, with a larger increase in cortisol levels producing a small reduction in the T:C ratio. The secondary purpose was to identify what relationships, if any, existed between the changes in strength, power, and hormonal concentrations. Statistical analysis revealed some positive small to moderate relationships between strength and power. However, these relationships seem to be unobtainable throughout a competitive season due to the large increases in performance (in the predictor variables) needed to elicit change.

Similar to previous studies, strength was maintained (−1.7 kg; −1.2%) in the upper body and improved (16.0 kg; 8.5%) in the lower body throughout the competitive season even with a reduction of resistance training volume (2,10,35). Numerous factors are reported to influence strength adaptations to resistance training (2,26,34). Baker (2) reported that upper-body strength in college-aged athletes could be increased (4.9%) but only maintained in professional athletes during a competitive season. It has been suggested that lack of strength gains in professional athletes is likely due to their greater strength training background, which may reduce the scope for further strength improvements (2,4). It is also likely that the variation in training modality that occurs in football codes influences adaptation. Specifically, the athletes in this study performed combinations of skill, tactical, strength, power, speed, and aerobic training sessions. As a result of this wide variety of different training stimuli performed and the need for recovery, some of these physical qualities may only be trained once a week during some points of the in season phase. Such combinations of training stimuli may also produce numerous challenges to the body's adaptive processes (26).

In the present study, the lack of improvement in upper-body strength (−1.2%) throughout the competitive season may have been due to a decreased resistance training volume (1.3 and 2.2 sessions per week, backs and forwards, respectively). Indeed, a meta-analytic review of strength training protocols (34) concluded that trained athletes can improve strength by performing a strength training session of 8 sets per muscle group 2 times per week. This supports findings from the current study that, although the forwards did perform on average 2.2 resistance sessions per week in the competitive season, only one of these sessions had a specific upper-body strength focus, thus preventing athletes from achieving the possible training volume required to increase upper-body strength.

There was a small 8.5% increase in lower-body strength throughout the competitive season. This increase suggests that training status and performing combination training may not significantly affect gains in strength; rather, increases in strength may more likely be due to frequency and volume of training. Indeed, heavy lower-body resistance exercise was performed twice a week for the forwards (1 strength session and 1 power session) and once for backs (1 power session). Additionally, the forwards typically performed scrum training once a week, which consisted of maximal isometric contractions of the lower body (in a position that is similar to a horizontal hack squat), whereas the backs completed resisted sled sprinting once a week. It is possible that this combination of gym- and field-based lower-body resistance training provided adequate stimulus to increase lower-body strength across the entire group. One may speculate that the reduced gym-based resistance training during the competitive season provided adequate stimulus to maintain upper-body and lower-body strength, but it was the additional non-gym-based lower-body activities (e.g., scrum and resisted sled training) that could have contributed to the increase in lower-body strength. Therefore, changes in strength over a competitive season seem to be related to the frequency/volume of a conditioning stimulus requiring increased force outputs or load rather than effects of concurrent training or training status.

The results of the present study are consistent with previous literature in that a small decrease in lower-body power (−175 W; −3.3%) was observed throughout a competitive season, whereas power in the upper body was maintained (−40 W; −3.4%) (2,18,19,35). Unfortunately, limited data exist that quantify changes in power in elite athletes over the course of a training or competition phase. Similar to the data reported earlier on strength, the changes observed for power may be due to numerous factors including training volume and stimulus, inadequate recovery, and training status (2,4,18,26).

As with strength adaptations, positive adaptations in power are likely to require an adequate training stimulus. The reduction of training load throughout the competitive season may have led to insufficient stimulus provided to promote positive adaptation in power. Indeed, the athletes only completed 1 gym-based power session each week on average throughout the competitive season. Furthermore, the introduction of additional training goals (e.g., skills) throughout the competitive season further reduced the potential training volume that could be performed in each of the numerous aspects of conditioning throughout each week.

Decreases in power may also be due to a compromised physical development caused by residual fatigue induced by limited recovery time between successive matches and training sessions (18). Repeated residual fatigue, caused by weekly competition and training stress without adequate recovery, may lead to athletes being in an “over-reached” state, resulting in a short-term decrement in performance (22).

It has been previously shown that performance gains are reduced in elite athletes with a high training status (2,4). For example, Baker and Newton (4) assessed power in subelite rugby league athletes over a 4-year period and reported that initial increases in power diminished as athletes became stronger (and progressed to an elite level). This was eventually followed by a cessation of power improvements by the end of the second year. The lack of improvement may suggest that elite level athletes need a greater volume of training and/or perhaps a more specific stimulus to enhance power production. Therefore, the lack of improvement in upper-body and lower-body power may have been due to a combined effect of (a) inadequate recovery between matches, (b) insufficient training stimulus (intensity and frequency), and (c) athlete's training status.

There was a large within-subject variation in hormonal data over the competitive season (Table 3). However, moderate increases in testosterone (54%) and cortisol (94%) were observed throughout the season. A small reduction (22%) in the testosterone to cortisol ratio (T:C ratio) also occurred due to the larger increase in cortisol over the competitive season. There is a limited body of knowledge regarding hormonal changes in athletes over competitive seasons. Nonetheless, potential mechanisms for the increase in testosterone and cortisol observed may include factors such as deflated pretest values, training volume, recovery, and psychological variables (14,15,25,29,36).

Increases in testosterone observed throughout the season may have been due to a diminished resting level of testosterone on the first testing occasion. During periods of heavy or high-volume training, levels of testosterone can be significantly reduced (25,36). It may be possible in the current study that during the initial testing session, athletes may have been experiencing a reduced testosterone level as a result of the prior intense 7-week preseason training phase.

The increase in testosterone throughout the 13-week season may also be due to a “recovery” of the endocrine system caused by the reduction of training load throughout the season (for training loads see Table 1). Increases in testosterone have previously been reported after an 11-week competitive soccer season (25). Kraemer et al. (25) suggested that the recovery/increase in testosterone reflected the dramatic reduction of training stress throughout the season. Additionally, increases observed in testosterone may also be in part due to psychophysiological mechanisms. The participants in the current study lost their first 5 games of the season but then went onto win 7 of their final 8 games. Etias (15) reported that humans undergo specific endocrine changes in response to victory or defeat and that the victor responds with a greater increase in testosterone than the loser.

Periods of intense training have previously been reported to increase levels of cortisol (24,25). In contrast to testosterone, one may speculate that the large volume of training performed in the preseason in the current study may have led to an increased cortisol level at the initial testing session. Interestingly, there was a continual increase in cortisol throughout the competitive season even though there was a reduction in training volume. Although somewhat speculative, this may have been caused by the difference in training intensity between the preseason and competitive season phases. By reducing the training volume throughout the competitive season, athletes may be less affected by fatigue and are able to train at higher intensities (for shorter periods). The greater intensities of training during the competitive season may place additional physical stress on the athlete in comparison to the high-volume, moderate-intensity, preseason training. Furthermore, when comparing preseason and competitive season phases, there was a greater amount of physical impact and contact throughout the competitive season in comparison to the preseason training. This higher intensity of training coupled with the added volume of physical impact may have added to the increase in cortisol observed.

Increases in cortisol after a single game of rugby union have been previously reported (14). The authors concluded that a minimum of 5 days of rest (or light training) was needed to adequately recover from the demands of the game (14,21). The participants in the current study were generally performing intense and physically demanding training by the second or third day after the game. Therefore, based on the findings from Elloumi et al. (14), the participants may not have recovered fully. This inadequate recovery after games in addition to the training demands and successive weekly competition may have caused a gradual increase in cortisol levels over the competitive season.

Psychological factors may also add to the increased level of cortisol. Previous investigations have reported a statistically larger increase in cortisol after competition than in simulated competition or training (23,33) Additionally, increased cortisol levels have been reported before competition in instances where the perceived importance of the outcome is greater (29). Due to the professional nature of the sport, the perceived importance of the outcome is regularly high. Athletes also have additional pressure to perform, as poor performance can lead to nonselection, which can ultimately lead to a loss of employment. This additional pressure to perform can increase the level of stress. Stressful situations have been reported to be one of the best-known triggers for an increase in cortisol levels (1).

The statistical analysis used in the current investigation allowed for a better understanding of not cause and effect but rather change and effect between measures. It should be noted that strength and power measures were not calculated at the same time (24-48 hours apart) due to structure of the training week. The results from the present investigation indicated that upper-body power may be improved by increasing upper-body strength. The relationship supports the contention that increases in power can be attained through increased strength (3). However, similar findings were not reciprocated in the lower body in which a trivial relationship between changes in box squat and jump squat was observed. The differences between the relationships of the upper body and lower body may be due to the differences in the kinematics of the movements. The bench press and bench throw both employ the stretch-shortening cycle (SSC); only the jump squat exercise uses the SSC in the lower-body exercises assessed. The box squat differs in that at the end of the eccentric phase there is a pause (sitting on the box) before the commencement of the concentric phase, minimizing or eliminating the SSC. These differences may potentially explain the disparity in the relationships observed between the upper body and lower body. Findings from the present study also suggest that increases in strength can be obtained through increasing power output, albeit to a much lesser extent. Caution should be taken when interpreting these findings because, although some small to moderate relationships were observed, the actual observed changes in performance measures over the competitive season were much smaller than the within SDs needed to obtain the predicted changes in performance. Therefore, many of the relationships would be near unobtainable in elite athletes over a competitive season. For example, to increase jump squat power by 2.6%, you would need to increase box squat strength by 18%, whereas the observed change in box squat over the competitive season was only 8.5%.

The results also revealed mostly trivial but unclear findings for hormonal relationships with the exception of a small relationship between cortisol and box squat. However, as with the performance measures, the large within SD of cortisol needed to increase box squat strength is very large and would be virtually unobtainable and may have a negative effect on other adaptation processes. Further research may want to observe the relationships between an acute rise in cortisol and it effects on box squat strength.

The findings from the current study revealed that maximal upper-body strength can be maintained, whereas lower-body strength may be improved throughout a competitive rugby union in season despite a decreased volume of resistance training. In contrast, power was negatively affected by the competitive season, especially in the lower body. Although many factors may contribute to changes in strength and power over a competitive season, it seems that these measures may be primarily affected by training load (intensity and volume). Additionally, it seems there may be some crossover effect between performance measures; however, the required change in many of the predictor measures to improve a dependent measure may be too large to obtain throughout a competitive season. Therefore, it may be suggested that for improvement in individual performance measures, athletes need to train specifically for that measure to maximize potential adaptation, at least in elite rugby union athletes over a competitive season.

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Practical Applications

Findings from this investigation suggest that volume and intensity of training is the primary factor in enhancing performance measures in elite rugby union athletes over a competitive season. We suggest that athletes of a high training status and longer training history may need to train more specifically to enhance performance in individual performance measures. In addition to training specificity, an increase in resistance training volume may be needed to improve levels of strength and power within a competitive season of concurrent training. We suggest that 2 resistance sessions for each major muscle group may be enough to maintain strength and power; but greater than 2 resistance sessions (or 2 plus additional supplemental non-gym-based resistance training, i.e., weighted sled sprinting) may be needed to improve strength and power in elite rugby union athletes during a competitive season. Whether such training can be performed while still allowing the athletes to recover from the game and training loads remains unknown.

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Acknowledgments

This study was funded by the Waikato Rugby Union and the Tertiary Education Commission. The results of the present study do not constitute endorsement by the National Strength and Conditioning Association.

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Keywords:

elite athletes; cortisol; resistance training; testosterone

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