Rugby union is a collision-based field sport, intermittent in nature, requiring high levels of endurance, strength, power, agility, and speed, including proficiency in match-related skills (1,12,13). Match analysis has detailed a highly varied and intermittent game, with a wide degree of physical situations using all energy systems (12). Forwards in particular have been identified as requiring high levels of strength for scrumming and contact-wrestling activities, whereas backs perform a higher frequency of sprints per match compared with that done by forwards. In rugby league, player sprint performance has been related to strength and power (4), whereas muscular strength has been frequently demonstrated to discriminate playing levels within many collision-based field sports (2,7,17,18). Although these findings highlight the importance of high-strength development as a critical requirement for rugby union players, the need for development of other physical characteristics and the training structure of professional rugby (i.e., limited time for physical conditioning and the need for concurrent training) can affect maximum strength development.
Although maximizing the long-term development of strength is one of the primary goals of conditioning programs, much of what we know about the neurological and morphological adaptations to resistance training arise from short-term (i.e., commonly 8- to 12-week interventions) investigations involving relatively untrained or inexperienced participants. This is a serious limitation of current knowledge because the principle of diminished returns dictates that initial improvements in muscular function are easily invoked and further improvements are progressively harder to achieve (27). Very few studies have examined the magnitude of changes in strength over relatively longer periods of time and even fewer have done so with very well-trained athletes (3,6,8,19,20). An investigation involving incoming intercollegiate Division IA basketball athletes reported upper and lower body strength increases of 24 and 32%, respectively, over a 4-year period (21). Although these improvements are of a similar magnitude to those observed in short-term research studies, changes in strength have been observed to be much smaller in highly trained athletes (6,8,19,20). Professional rugby league athletes with at least 3 years of resistance training experience were reported to improve maximal lower body strength by 14% across a 4-year period (8) and maximal upper body strength by 11% across a 6-year period (3). Furthermore, a comparison of upper body strength development between elite and subelite rugby league athletes illustrated considerable difference in the magnitude of change over a 6-year period with increases of 6 and 24% observed, respectively (3). Finnish national champion weightlifters were observed to show small, nonstatistically significant improvements in maximal strength after 1-year of training (19) and a significant improvement of 2.8% in total weightlifting result after 2 years of training (20). Collectively, these results illustrate that highly trained athletes have a limited potential for further strength development even over long-term periods of intense training and highlight the importance of effective program design. Although these findings provide indirect observations about the theoretical construct of the principle of diminished returns, to date, there is a paucity of research empirically testing this hypothesis (27), especially in highly trained athletes.
Maximizing the long-term strength development of team sport athletes is a primary goal for strength and conditioning coaches. Despite this, there is very limited research investigating long-term strength development in highly trained professional team sport athletes, especially rugby union athletes. Although extensive research has examined the magnitude of change in strength expected over short periods of time in relatively untrained subjects, little scientific evidence exists regarding the magnitude of change in strength that can be expected over a long-term period in highly trained athletes (6,8,19,20). Importantly, no such evidence is available for professional rugby union athletes. Furthermore, very limited evidence is available regarding the factors that may influence the ability to adapt to resistance training, and thus the magnitude of change in strength, in highly trained rugby union athletes (i.e., “Can the older and very strong athletes still significantly improve their strength?” and “Does a highly trained athlete need to increase lean muscle mass to significantly improve their strength?”). Therefore, the primary purpose of this study was to assess the magnitude of upper and lower body strength changes in professional rugby union players after 2 years of training. An additional purpose was to examine if the changes in strength were influenced by starting strength level, lean mass index (LMI), or chronological age.
Experimental Approach to the Problem
This longitudinal investigation tracked maximal strength and body composition over 3 consecutive years in highly trained, professional rugby union athletes to examine the long-term adaptations to resistance training. Maximal strength in the bench press and back squat and body composition was assessed using a 1 repetition maximum (1RM) test during preseason resistance training sessions each year. The participants completed 1RM assessments at the same time of day (i.e., first training session of the day), with squat and bench press 1RM tests conducted on separate days every 3–4 weeks throughout the preseason period each year. Assessment of body composition was performed at the same time of day (i.e., before the first training session of the day) every 2 weeks throughout the preseason period each year. All the participants were highly experienced athletes from the same professional club, and they completed a very rigorous training program throughout the duration of this study consisting of numerous resistance, conditioning and skills training sessions every week.
Twenty professional rugby union athletes (12 forwards and 8 backs) with extensive resistance training experience fulfilled all the requirements of this investigation (Table 1). Only the athletes who had a minimum of 2 years of full-time employment in a professional rugby union club in 2007 were considered to be eligible to participate. At the start of this investigation, the participants' length of professional employment ranged from 2.5 to 13.8 years with an average of 6.6 ± 3.2 years, whereas the length of resistance training experience ranged from 4.5 to 17.5 years with an average of 10.5 ± 3.3 years. Nineteen athletes completed all the upper body strength assessments, whereas 11 athletes completed all the lower body strength assessments. The participants gave their written informed consent and voluntarily completed the requirements of this investigation as part of their normal club training sessions and. This study was approved by the university's human research ethics committee.
Throughout the duration of the study, the participants completed a periodized training program consisting of between 4 and 12 training sessions per week. The average number of resistance, conditioning, and skills sessions including matches per week is outlined in Table 2. Resistance training programs were individualized based on each athlete's physical strengths and weaknesses and the presence of any injury. The resistance training program was designed to maximize the long-term development of strength and power. During the preseason phase, the resistance training sessions were typically categorized as hypertrophy (i.e., 60–75% 1RM, 20–25 sets of 10–15 reps) hypertrophy strength (i.e., 65–90% 1RM, 20–25 sets of 3–15 reps), strength (i.e., 80–100% 1RM, 15–20 sets of 1–6 reps), or power (i.e., 50–85% 1RM, 15–20 sets of 1–6 reps) and cycled in 3-week blocks with a recovery or lighter week being the last week of each cycle. The precompetition phase was characterized by lower volume (i.e., 15–20 sets of 1–10 reps), higher intensity (i.e., 75–100% 1RM) strength, and power sessions, whereas the competition phase consisted primarily of maintenance programming (i.e., 80–100% 1RM, 20–25 sets of 3–12 reps). At the completion of the season, the athletes involved with their national representative team followed the direction of the national program. The participants not involved with representative teams completed hypertrophy or strength-based sessions aimed at maximizing long-term strength development throughout the club season phase. Specific emphasis was placed on addressing each individual's athletic performance limitations. Individually designed training programs were prescribed with a methodical, progressive overload outlook. Recovery and off-season programs were general in prescription.
A typical upper body training session commenced with 1–3 shoulder warm-up exercises targeting rotator cuff and scapular stability. In general, the number of sets ranged from 15 to 25, depending on the individual requirements. Between 3–4 sets of progressively increasing load were performed before 2–3 sets at maximal intensity for that session's required load. Only multijoint exercises were used and the ratio of push-pull movements was prescribed individually to ensure muscular balance in each athlete. Typical exercises included chin-ups, bent-over rows, bench pull, flat, incline, and shoulder press, using barbells or dumbbells.
A typical lower body session commenced with 1–2 lower body stability or technique oriented warm-up exercises of submaximal intensity. The number of work sets was generally less than the upper body sessions, ranging from 15 to 20. Similar to upper body strength training sessions, between 3–4 sets of progressively increasing load were performed before 2–3 sets of maximal intensity at that session's required load. Only multijoint exercises were prescribed with the exception of supplementary hamstring and gluteal isolation exercises, completed toward the later stages of the program. Typical multijoint exercises included deadlifts, squats, clean pulls, step-ups, incline leg press, and power cleans.
Conditioning sessions involved a variety of aerobic and anaerobic conditioning training modalities during the duration of the study period. During the preseason phase, conditioning sessions comprised predominately running, although bike, crosstraining, swimming, and boxing sessions were also used. The individuals were prescribed between 2 and 4 conditioning sessions per week of varying intensity (i.e., 6–9 rating of perceived exertion [RPE] using the modified 1–10 scale) and duration (30–60 minutes), depending on their individual positional requirements. During the precompetitive and in-season phases, technical and tactical skill sessions were the predominant form of conditioning, incorporating a high conditioning running component, supplemented where necessary with small sided games. Additional conditioning sessions were prescribed on an individual player basis in accordance to their needs analysis. The in-season conditioning sessions were of a similar intensity (i.e., 6–9 RPE), but much shorter duration (maximum 30 minutes).
Skill sessions involved components of individual player skill development, unit training (i.e., position specific specialist small team technique and tactics), full team training, simulating match play with varying levels of physical contact ranging from no contact, to pads, to full contact drills. The number of sessions per week ranged from 2 to 4 and were of varying lengths (45–120 minutes) and intensities (RPE of 3–7). In-season, postmatch recovery and travel were factors that influenced the frequency (between 2 and 3), duration (30–60 minutes), and intensity (RPE of 2–7) of skill sessions.
Maximal Strength Assessment
The bench press and back squat 1RM were used to assess maximal upper body and lower body strength, respectively. Regular assessments were conducted throughout the preseason period each year with testing occurring at the same time of the day, on the same day of the week for each exercise every year. The 1RM protocol involved participants completing a series of 3–4 warm-up sets of increasing load each separated by 3 minutes of recovery. A series of maximal lift attempts were then performed until a 1RM was obtained. No more than 5 attempts were permitted with each attempt separated by 5 minutes of recovery. This protocol has been used frequently in previous research for the assessment of maximal dynamic strength (5,10,11) and reliability of these protocols have been established previously (23–25). A free-weight bench press rack was used to test bench press 1RM. Only trials in which participants lowered the barbell to their chest and returned it to full extension of the arms without bouncing the barbell off their chest or losing contact between the bench and their hips or the floor and their feet were considered successful. A free-weight squat rack was used to test squat 1RM. The participants were required to lower the barbell to a depth equivalent to at least 90° of knee flexion for the attempt to be considered successful. This depth was monitored during testing using a linear position transducer (GymAware, Kinetic Technology, Canberra, Australia) attached to the barbell and visually by the same experienced tester. All the participants were very experienced with the bench press and squat 1RM protocols, having performed the assessments frequently for a minimum of 2 years before 2007. Assessment of 1RM occurred frequently throughout the preseason phase each year, and only the highest 1RM of the year was included in the analysis (i.e., comparisons were made between the highest strength level achieved during the preseason of 3 consecutive years to determine the long-term changes in strength rather than short-term fluctuations because of deconditioning during the off-season, etc.).
Body Composition Assessment
The same experienced, International Society for the Advancement of Kinanthropometry accredited anthropometrist performed skinfold thickness assessments in accordance with standard methods throughout the duration of this study. The following 7 sites were measured using calibrated skinfold callipers (Harpenden Skinfold Callipers) triceps, subscapular, biceps, supraspinale, abdomen, thigh, and calf. Body mass was assessed using the same set of calibrated electronic scales. The between test technical error for sum of 7 skinfolds and body mass was 2 mm (i.e., 3.0%) and 0.01 kg (i.e., 0.01%), respectively, based on repeated measurements of 10 athletes. The LMI was calculated using methods described by Duthie et al. (14) as an indicator of fat-free mass (LMI = mass/sum of 7 skinfoldsx, where x is 0.13 for forwards and 0.14 for backs). Urine specific gravity was assessed regularly to ensure a consistent level of hydration.
A general linear model with repeated-measures analysis of variance followed by Bonferroni post hoc tests was used to examine the changes in strength throughout the duration of the study. Mean effect sizes (ESs) were also calculated to examine the practical significance of the changes in strength. The strength of the effect was classified based on Cohen (9), which suggests ES of 0.2, 0.5, and 0.8 to represent a small, moderate, and large effect, respectively. Relationships between the changes in strength and starting strength level, LMI, and age were evaluated using Pearson's correlation coefficient (r). The strength of the correlation coefficient was determined based on classifications outlined by Cohen (9), where r = 0.10–0.29 has a small effect, r = 0.30–0.49 has a moderate effect and r ≥ 0.5 has a large effect. Statistical significance for all analyses was defined by p ≤ 0.05, and results were summarized as means ± SDs.
Statistically significant differences among 2007, 2008, and 2009 were observed in a number of variables (Table 1). Statistically significant changes in the LMI, bench press 1RM, and bench press 1RM:BM were observed in both 2008 and 2009 (Table 3). Practically relevant improvements in squat 1RM and squat 1RM:BM were also observed in 2008 and 2009, but these changes did not reach statistical significance (Table 3). Significant negative relationships that had a large effect were observed between strength level in 2007 and the percent change in strength in 2008 and 2009 for both the bench press and squat (Figure 1). These data indicate that 32–51% of the variance in maximal upper body strength percent change and 41–46% of the variance in maximal lower body strength percent change was explained by starting strength level. Significant positive relationships that had a large effect were also observed between the percent change in the LMI and percent change in lower body strength but not upper body strength (Figure 2). These data indicate that 6–10% of the variance in maximal upper body strength percent change and 44–77% of the variance in the maximal lower body strength percent change was explained by the percent change in the LMI. No relationship was observed between age in 2007 and the percent change in either upper body or lower body strength (Figure 3). Specifically, only 0–12% of the variance in maximal strength percent change was explained by age in 2007.
This investigation is the first to document the long-term adaptations to resistance training in professional rugby union players. The primary findings of this study were (a) maximal upper and lower body strength was increased by 6.5–11.5% after 2 years of training; (b) the magnitude of the improvement was negatively associated with initial strength level (this study provides some of the first data and the strongest evidence to date supporting the theoretical construct of the principle of diminished returns); (c) the magnitude of improvement in lower body maximal strength was positively related to the change in the LMI (an indicator of hypertrophy); and (d) the magnitude of improvement was not associated with the age of professional rugby union athletes.
Despite the well-trained nature of the athletes at the commencement of the 2-year training block and the concurrent training essential for improving performance in rugby union athletes, considerable increases in strength were observed in both the upper body and lower body. These findings support those previously observed in rugby league athletes in whom similar training characteristics and long maintenance phases are required (6,8). The 11.5 and 10.8% increase in maximal upper and lower body strength observed over 2 years of training is comparable with the 6.0% (6) and 14.1% (8) improvement in upper and lower body strengths previously reported for highly trained rugby league athletes. Despite the much greater work performed by professional athletes during long-term training programs, the adaptations observed are of a considerably smaller magnitude than those reported by many short-term research investigations involving relatively untrained, inexperienced participants (e.g., 28% increase in squat 1RM after 10 weeks of resistance training ). The current findings provide additional evidence that highly trained athletes have a limited potential for further strength development even over long-term periods of intense training (3,6,8,19,20). Additionally, the current observations further demonstrate the importance of effective program design involving sophisticated resistance training techniques and a clear understanding of the multitude of factors that affect adaptation in professional team sport athletes.
Significant negative relationships were observed between initial strength level and the magnitude of change in both upper and lower body strength after 2 years of training (r = −0.569 to −0.712, i.e., 32–51 and 41–46% of the variance in maximal upper and lower body strength changes, respectively, was explained by starting strength level). These results provide some of the first data and certainly the strongest evidence to date for elite athletes supporting the theoretical construct of the principle of diminished returns which dictates that initial improvements in muscular function are easily invoked and further improvements are progressively harder to achieve (i.e., the magnitude of potential for training-induced improvement decreases as strength and training experience of the athlete increases) (8,27). It is theorized that despite all the participants being exposed to a similar volume of resistance training, the relatively weaker athletes had a greater capacity for adaptation within the neuromuscular system (i.e., a larger window of adaptation). If similar rates of improvements are to be achieved, the stronger participants may require a greater stimulus because of the smaller window of adaptation for strength improvement these athletes have as a result of their highly developed neuromuscular system. It is unknown if this can be achieved through sophisticated program design or if the time necessary to devote to a greater rate of improvement in these athletes limits the ability for development in other important performance areas and increases the risk of overtraining.
It has been well documented that increases in muscle cross-sectional area are strongly associated with increased strength (15,16,22). This study reflects these results in an applied setting with significant correlations observed between the magnitude of lower body strength gain and the change in LMI (r = 0.692–0.880, i.e., 44–77% of the variance in lower body strength change was explained by the change in LMI). No significant relationship was observed between the magnitude of upper body strength gain and changes in LMI (r = 0.244–0.314, i.e., only 6–10% of the variance in upper body strength change was explained by the change in LMI). This is theorized to be a reflection of the greater potential for hypertrophy of the lower body compared with upper body musculature. Although not a direct measure of muscle mass or cross-sectional area, the LMI can be considered an indicator of muscle hypertrophy. The significant relationship between strength and LMI gain demonstrates the importance of hypertrophy to enhancing lower body maximal strength in professional rugby union players. Therefore, if further improvements in strength are to be achieved in such highly trained athletes, training programs need to be designed for continued muscle hypertrophy and this can be achieved despite high volumes of aerobic and skills training. The significant 2.8% increase in LMI observed in the current investigation illustrates that muscle hypertrophy is still achievable under these circumstances.
The average age of the participants in this study was higher than in other long-term studies involving highly trained athletes (6,8,26). Despite this, the results indicate that older athletes were still able to increase strength. Specifically, there were no statistically significant relationships observed between the athlete's age at the start of the investigation and the magnitude of change in maximal strength after 2 years of training. Although there were nonsignificant trends toward a negative relationship between initial age and upper body strength gain (r = −0.313 to −0.345, p = 0.148–0.191, i.e., 10–12% of the variance in upper body strength change was explained by initial age), changes in lower body strength showed no association with initial age (r = −0.068 to −0.152, p = 0.655–0.842, i.e., 0–2% of the variance in lower body strength change was explained by initial age). Interestingly, in 2007, there was a trend toward a positive relationship between age and upper body strength level (r = 0.389, p = 0.100) and no relationship observed between age and lower body strength level (r = −0.289, p = 0.388). These observations suggest that the higher initial upper body strength level of older athletes may have a strong confounding impact on the correlations observed between age and change in strength. Nevertheless, it is clear that changes in lean muscle and an athlete's initial strength level are more important factors to consider than chronological age when designing training programs that maximize the development of strength in highly trained athletes. This is an encouraging finding for strength and conditioning coaches because it demonstrates that older athletes are still able to considerably improve strength.
Another interesting observation worthy of discussion is the timing of improvements over the 2-year training period. Increases of 7.3% (p = 0.001, ES = 0.66) and 10.6% (p = 0.198, ES = 0.50) in bench press and squat 1RM strength, respectively, were observed during the first year of training (i.e., 2007–2008). In contrast, increases of only 4.0% (p = 0.099, ES = 0.38) and 0.4% (p = 0.857, ES = 0.02) in bench press and squat 1RM were observed during the second year of training (i.e., 2008–2009), leading to improvements of 11.5 and 10.8% across the 2 years of training (i.e., 2007–2009). These figures quite clearly demonstrate a far more pronounced yearly increase in strength during the first year of the training period observed, especially with lower body strength. There are many factors that may have contributed to these observations (i.e., less effective program design, increased quantity of match time leading to more match-related soreness (26), increased prevalence of injury, shift in program emphasis, player motivation, etc.), but the primary driver was theorized to be associated with differences in the training load performed between the first and second years of training. The number of resistance training sessions involving the bench press remained relatively similar from 2007 (17.1 ± 7.7) to 2008 (16.3 ± 6.4, p = 0.627) and 2009 (14.6 ± 8.5, p = 0.307). However, the number of resistance training sessions involving the squat showed a trend toward increasing from 2007 (10.9 ± 6.6) to 2008 (13.0 ± 6.4, p = 0.275) and was significantly lower in 2009 (6.3 ± 4.4, p = 0.021). Similar results were observed in the number of work sets performed of the bench press (2007—51.4 ± 25.5; 2008—51.3 ± 23.2, p = 0.981; 2009—40.8 ± 26.0, p = 0.197) and the squat (2007—40.7 ± 25.4; 2008—51.6 ± 30.2, p = 0.244; 2009—21.6 ± 15.4, p = 0.018). Although these data do not capture all exercises that target the prime movers in the bench press and squat, it provides a strong indication of the changes in upper and lower body resistance training volumes throughout the duration of the study. These differences in the volume of resistance training performed were because of injury and a shift in training emphasis for individual players.
Professional rugby union athletes with extensive resistance training experience can expect to see strength gains of approximately 6.5–11.5% in both the bench press and squat after 1–2 years of training. These improvements can be expected regardless of the athlete's age and are associated with an increase in lean mass (squat only). Given the strong relationship between increases in the LMI and increases in strength, it appears particularly important for training programs to be designed for continued muscle hypertrophy. Even in elite level rugby union athletes, this must be achieved in the face of high volumes of aerobic and skills training. Furthermore, the degree of strength improvement is related to initial strength level with larger improvements observed in athletes with relatively lower levels of strength regardless of age.
Improvement in strength is highly related to increased lean muscle mass in highly trained athletes. Strength and conditioning coaches should be mindful to include a level of hypertrophy training in resistance training programs for highly trained athletes requiring increases in strength.
The magnitude of strength improvement is related to initial strength level with greater improvements observed in relatively weaker athletes. Strength and conditioning professionals should be aware of the greater programming detail required for continued development of strength in highly trained athletes compared with relatively weaker athletes even within the same professional organization.
Age does not appear to limit the potential to adapt to strength training within a group of highly trained professional rugby union athletes.
No sources of funding were provided for this investigation. The authors would like to thank the players and coaching staff at the Emirates Western Force for their participation in the study.
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