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Effects of an Off-Season Conditioning Program on the Physical Characteristics of Adolescent Rugby Union Players

Smart, Daniel J.; Gill, Nicholas D.

Journal of Strength and Conditioning Research: March 2013 - Volume 27 - Issue 3 - p 708–717
doi: 10.1519/JSC.0b013e31825d99b0
Original Research
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Smart, DJ, and Gill, ND. Effects of an off-season conditioning program on the physical characteristics of adolescent rugby union players. J Strength Cond Res 27(3): 708–717, 2013—The aims of the study were to determine if a supervised off-season conditioning program enhanced gains in physical characteristics compared with the same program performed in an unsupervised manner and to establish the persistence of the physical changes after a 6-month unsupervised competition period. Forty-four provincial representative adolescent rugby union players (age, mean ± SD, 15.3 ± 1.3 years) participated in a 15-week off-season conditioning program either under supervision from an experienced strength and conditioning coach or unsupervised. Measures of body composition, strength, vertical jump, speed, and anaerobic and aerobic running performance were taken, before, immediately after, and 6 months after the conditioning. Post conditioning program the supervised group had greater improvements in all strength measures than the unsupervised group, with small, moderate and large differences between the groups\x{2019} changes for chin-ups (9.1%; ±11.6%), bench-press (16.9%; ±11.7%) and box-squat (50.4%; ±20.9%) estimated 1RM respectively. Both groups showed trivial increases in mass; however increases in fat free mass were small and trivial for supervised and unsupervised players respectively. Strength declined in the supervised group while the unsupervised group had small increases during the competition phase, resulting in only a small difference between the long-term changes in box-squat 1RM (15.9%; ±13.2%). The supervised group had further small increases in fat free mass resulting in a small difference (2.4%; ±2.7%) in the long-term changes. The postconditioning differences between the 2 groups may have been a result of increased adherence and the attainment of higher training loads during supervised training. The lack of differences in strength after the competition period indicates that supervision should be maintained to reduce substantial decrements in performance.

Sport Performance Research Institute New Zealand, AUT University, Auckland, New Zealand

Address correspondence to Daniel J. Smart, daniels@nzasni.org.nz.

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Introduction

Rugby union is a high-intensity intermittent contact based team sport of an 80-minute duration. During competition, players have been shown to travel over 7 km, requiring numerous maximal sprints, and experiencing large amounts of physical contact at the tackle, ruck, and scrum situations (7,8,11,32,34). Because of the diverse physical demands experienced during competition, the physical components required for success vary. Training in rugby union players has to therefore accommodate these demands, and at semiprofessional level and above, structured resistance training for hypertrophy, strength, and power; aerobic and anaerobic conditioning; and speed training occur in conjunction with the skill-based team sessions (10). However, in adolescent rugby union players, in-season training commonly consists of 2 skill-based team sessions, whereas an off-season conditioning program is sometimes supplied to the players without demonstration or supervision.

Physical training in adolescents, in particular resistance training, is well documented and is thought to be beneficial by increasing strength, decreasing injury rate and improving sport performance (12,22,26). Because of the potential exclusions of future elite performers within talent identification programs, research has shifted focus to talent and long-term athletic development, highlighting the importance of structured training in order to increase young athletes' training age for future elite performance (33,38). Nonetheless, there is a lack of research that specifically investigates the effect of training on talented adolescent athletes. Furthermore, studies that have trained adolescents have usually investigated the direct effects of a training intervention, without a long-term follow-up on the persistence of the physical changes or the difference in changes relative to age.

Supervision of adolescent athletes during resistance training by an experienced strength and conditioning coach is recommended primarily for safety (13). In addition, direct supervision of resistance training sessions has also been shown to increase adherence and enhance the increases made in strength. Adolescent rugby league players have shown marked increases in 3 repetition maximum (RM) bench press and squat (29 and 37%, respectively) after supervised training compared with the same resistance training program unsupervised (15 and 23%, respectively) (6). It was thought the greater increases in strength were because of the greater training frequency and a greater intensity performed during the session. The results from this study illustrate the importance of supervision for strength development, and therefore, the role of supervision in other areas of physical development should also be considered (24).

Physical training and conditioning within adolescent rugby union players is generally unstructured and unsupervised; therefore, this study had 3 aims: to determine if a supervised off-season conditioning program enhances gains in physical characteristics compared with an identical unsupervised program; to establish the persistence of the physical changes during an unsupervised 6 month postintervention training period; and to determine the effect of age on the changes in physical performance as a result of the physical conditioning program. It was hypothesized that supervised training would elicit greater gains in physical characteristics compared with unsupervised training and that the differences in physical characteristics would be maintained 6 months postintervention.

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Methods

Experimental Approach to the Problem

This study examined the effect of a supervised off-season conditioning program in provincial representative adolescent rugby union players through a pre-post measures experimental-control research design. The players were tested in body composition, strength, vertical jump (VJ), speed, and anaerobic and aerobic running performance. The players were then randomly allocated into training groups for the 15-week intervention period. The supervised group trained 4 times a week (3 resistance training sessions and 1 speed and anaerobic-aerobic conditioning session) with an experienced strength and conditioning coach, and the unsupervised group was left to complete the same program in their own time. The players were tested on completion of the 15-week training intervention to determine the effects of the program, and again 6 months postintervention after an unsupervised competition period to establish the persistence of the effects. Statistical analysis allowed the use of age as a covariate to determine the effects of a change of age on physical changes.

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Subjects

Eighty-two provincial representative adolescent rugby union players volunteered to participate in the study. All the players meet the criteria for selection in the regional under-14, under-16 or under-18 representative rugby union teams for the season preceding the training period. The players were randomly selected into either a supervised training group or an unsupervised training group. As a result of dropout because of varied reasons (e.g., injury, illness, relocation), a total of 44 players completed the study (supervised n = 27; age [mean ± SD] 15.4 ± 1.4 years and unsupervised n = 17; age 15.1 ± 1.3 years). Before the commencement of the study, the players and their parents were briefed on the aims and procedures involved. Written inform consent was gained from all the players, whereas additional parental assent was gained from the players under the age of 16. This study was approved by the Auckland University of Technology Ethics Committee, which upholds the legal requirements regarding the consent of minors.

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Procedures

Study Design

The study consisted of 3 phases (Figure 1). Phase 1 (preparation) commenced immediately after the pretest (Pre), which was performed 2 weeks postrepresentative rugby season during which the players performed no structured training. Phase 1 consisted of an unsupervised program of low volume aerobic running (3 sessions of 20–30 minutes at conversation pace) and 3 sessions of light gymnasium-based exercises (bench press, leg press, chin-ups, seated row, and single leg step ups—3 sets of 10 repetitions) over a period of 4 weeks. This phase was used to prepare the players for the intensive intervention period and act as a form of active recovery postrugby season. Upon completion of this phase, the players reported to have completed approximately 50% of these sessions (an average of 3 sessions per week of both types of training).

Figure 1

Figure 1

Phase 2 (conditioning) represented the 15-week training intervention and was performed during the rugby off-season (summer). The phase was divided into three 4-week training blocks, with a 3-week unsupervised period after week 4, for the observation of the summer holiday period. During this phase, the supervised training group trained 4 times a week for an hour, supervised by an experienced strength and conditioning coach at a centralized location. The unsupervised group was posted the same training program at the beginning of each 4-week block and was asked to carry out the training at any facility at any time of their choosing. All the programs followed the same basic weekly structure with 3 resistance training sessions (full body, upper body, and lower body), 1 speed and anaerobic conditioning session and one unsupervised aerobic run (Table 1). At the conclusion of this phase, the players repeated the same testing battery that was performed for the pretest (post 1).

Table 1-a

Table 1-a

Table 1-b

Table 1-b

Phase 3 (competition) occurred immediately after the conditioning phase and consisted of an unsupervised 6-month in-season training program. During this period, training recommendations for strength, speed, anaerobic and aerobic conditioning was provided to maintain any improvements made over the intervention period. The prescribed training program was lower in frequency and volume as players generally participated in additional rugby training sessions and games each week (2 resistance training sessions a week, 4 sets of 6–10 repetitions; and, 1 session a week for speed and aerobic recovery, respectively, performing similar exercises and intensities as that performed during the conditioning phase). At the conclusion of this phase, the players repeated the same testing battery for a third occasion (post 2). All training programs and their respective progressions over the period of the study were written by experienced strength and conditioning coaches from the local professional rugby union team participating in the international Super Rugby competition.

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Training Load

During the study, training data were collected from all the players. All structured training or competition that the players participated in was recorded; specifically, the volume (duration) of exercise and a rating of perceived exertion (RPE) as indicated on a modified 10-point Borg scale (15). Training data were recorded each week during the training period and then once a month during the postintervention period. Training load was calculated by multiplying the duration of the training session by the RPE (5).

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Physical Performance Tests

The performance tests used in this investigation was part of the testing battery that was performed by all provincial academy rugby players; the level above the players in this study. All the tests were performed under the same conditions (prior activity, preceding nutrition, time of day and test order), and if players did not replicate behaviors similar to the previous tests, testing was rescheduled.

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Body Composition

Anthropometrical measurements included body mass, stature, and sum of 8 skinfolds (bicep, triceps, subscapular, abdominal, supraspinale, iliac crest, front thigh, and medial calf). Height was measured using a stadiometer, and body mass was measured on calibrated electronic scales (Tanita HD-316, Tanita Corporation, Tokyo, Japan). Each skinfold site was located and measured as per the International Society for the Advancement of Kinanthropometry guidelines (25) using a Slim Guide caliper (Creative Health Products, Plymouth, MA, USA). Percentage body fat was calculated from estimated body density (40) using the equation derived from Siri (29). Fat-free mass was calculated from the player's body mass and calculated body fat (Fat-free mass = body mass − (body mass × percentage body fat/100) (30). Data were only included if all technical errors of measurement were below the upper limits recommended by Perini et al. (27).

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Strength

One-repetition maximum was calculated for a series of resistance training exercises from a 6–10RM lift using the formula derived by Landers (23). The strength exercises included bench press, box squat, and chin-ups. Each exercise was assessed for correct technique, and only repetitions performed unassisted with correct technique were recorded.

During the performance of the bench press, the feet were to remain in contact with the floor and the buttocks, and lower back had to remain in contact with the bench throughout the lift. During the lift, the bar was to be lowered to the chest (with elbows at ∼90° not bouncing off the chest) and returned to the start position where the elbows were to be fully extended but not locked. Each player used a self-selected hand position, which remained consistent between tests. The box squat was performed by descending in a controlled manner to a seated position on a box where the player was instructed to pause briefly before returning to the standing position. The box height was adjusted to allow the top of the thighs to be parallel with the floor while in the seated position. The players used a self-selected foot position, which remained constant throughout all testing sessions. The chin-ups required a reverse underhand grip (palms facing toward face) to be used. The players were instructed to start from a stationary position with arms fully extended and complete a repetition with chin moving over the bar (1,4). The coefficients of variation (CVs) for similar strength testing protocols have been shown to be approximately 4.5% (1).

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Vertical Jump

Jump height was indicated by a countermovement VJ using a yardstick device (Swift Performance Equipment, NSW, Australia). The players were required to stand at the side of the yardstick and with flat feet extend their arm and hand above their head to mark the standing reach height. The players were then instructed to jump as high as they could and knock away the fingers of the yardstick. The players used a self-selected speed and depth for their countermovement and were able to use their arms and hands to assist with jump height. Jump height was calculated as the distance from the highest point reached during the jump and the standing reach height. Each player was allowed 2 attempts with 20-second rest between efforts. The highest jump was recorded for analysis (4). The intraclass correlation coefficient for this VJ protocol has been shown to be 0.93 (14)

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Speed, Anaerobic and Aerobic Running Performance

Speed, anaerobic and aerobic running performance was tested using the Metabolic Fitness Index for Team Sports (MFITS). The MFITS is made up of 3 components, each designed to indicate the capacity of the 3 metabolic systems. The first component consists of a 60-m sprint to test the phosphate energy system; the second component is a 400-m sprint to test the lactate (glycolytic) energy system; and the 1,500-m run as an indicator of aerobic capacity (21).

The MFITS was performed on a synthetic running track, and the players were required to wear soft-soled running shoes. The players were instructed to perform each aspect of the test maximally. The first component consists of 2 straight line speed repetitions over 60 m. The players were to start each sprint with their foot on a line 50 cm from the light beam of the first timing gate, from a stationary upright position, with no rocking back or forth before starting. The players completed the 60-m sprint in the lane formed by the electronic timing gates (Swift Performance Equipment), which was approximately 2 m wide. The time taken to complete 10, 20, 30, and 60 m for each sprint repetition was recorded, with the fastest used in the analysis.

After a 15-minute recovery, during the last 5 minutes, the players were required to complete a one lap jog of the 400-m track with two 40-m stride outs; players completed a 400-m sprint. The players were required to sprint maximally for the entire lap of the track while staying in their allocated lane. Groups of 8 players (1 per running lane) were started on the command ‘Set, Go.’ Simultaneously, allocated timers to each player started a stopwatch. The timers stopped the stopwatch when the player completed the 400-m run at the finish line. The time to complete the 400 m (to the nearest tenth of a second) was recorded.

After a 15-minute recovery, during the last 5 minutes, the players were required to complete a 1-lap jog of the 400-m track; the players completed a 1,500-m run. All the players commenced the run together starting at the 300-m mark on the track and completed 3 and three-quarter laps. The time to complete the 1,500 m was verbalized to the players as they crossed the finish line, which was then recorded to the nearest second. The CVs for the variables of the MFITS have been shown to be between 1.0 and 3.6% (31).

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Statistical Analyses

All data were analyzed using an Excel spreadsheet for analysis of pre-post controlled trials, which was set at 90% confidence limits (18). All data were log-transformed before analysis to reduce nonuniformity of error and adjusted for the age of each player as at the beginning of the study period. Data were back transformed and expressed as the parametric median, with errors expressed as CVs for the change scores and 90% confidence limits for differences in the within-group changes. The analysis was repeated using age as a covariate to determine the extent to which the effect of the training was because of changes in age. Standardized mean changes in performance and differences between the changes were used to assess magnitudes of effects by dividing the appropriate between-player standard deviation. Standardized effects were defined as using a modified Cohen scale: <0.2 = trivial, 0.2–0.59 = small, 0.6–1.19 = moderate, 1.2–1.99 = large, >2.0 = very large (19). The effect was deemed unclear if its confidence interval overlapped the thresholds for small positive and negative effects.

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Results

Differences in the supervised and unsupervised groups' pretest values were small for body mass, skinfold thickness, percent body fat, and 400-m time, and moderate for bench press 1RM. All other differences in pretest values were trivial or unclear.

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Conditioning Phase

The supervised and unsupervised groups anthropometric and performance test results are displayed in tables 2 and 3 respectively. At the conclusion of the conditioning phase, the supervised group had greater changes in strength, VJ and acceleration than the unsupervised group. The differences between the changes were small, moderate and large for chin-ups 1RM (9.1%; 90% confidence limits ±6.9%), bench-press 1RM (16.9%; ±7.0%) and box-squat 1RM (50.4%; ±12.2% - Figure 2) respectively; while there was a small difference between the increases in VJ height (4.2%; ±6.5%). There was a moderate difference in the change in 10-m sprint time (2.1%; ±2.5%); however the differences were unclear at 20 m, 30 m and 60 m. Furthermore, the unsupervised group had greater increases in skinfold thickness and percent body fat, resulting in small differences (8.7%; ±8.3% and 8.7%; ±7.4% respectively) between the groups changes in body composition. All other differences between groups' changes in body composition (e.g. mass) and running performance (e.g. 400-m sprint time) were trivial or unclear.

Table 2

Table 2

Table 3

Table 3

Figure 2

Figure 2

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Competition Phase

Over the period of the competition phase, the supervised group's strength tended to decline, however the only clear change was a moderate decrease in box-squat 1RM (17.9% ± 24.2% - Figure 2). The resultant differences between the supervised and unsupervised groups\x{2019} changes during this phase were large for box-squat 1RM (28.6%; ±16.3%), moderate for bench-press 1RM (14.1%; ±6.3%) and small for chin-ups 1RM (7.5%; ±5.3%). Fat free mass had small increases in the supervised group (2.7% ± 2.4%) and trivial increases in the unsupervised group (2.2% ± 2.3%). Consequently, the differences between the groups' changes from Post 1 to Post 2 were trivial. The small to moderate decreases (∼2.8%) in speed time (10 m, 20 m and 30 m) in the unsupervised group from Post1 to Post 2 resulted in differences between the groups changes for 10 m (moderate; 4.3%; ±2.4%), 20 m (small; 1.5%; ±1.8%) and 30 m (small; 2.2%; ±1.9%). All other differences between the changes over the period of the competition phase were trivial or unclear.

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Long-Term Changes

Although the supervised group showed decreases in strength over the competition phase, the long-term changes (Pre to Post 2) for bench-press 1RM (16.3% ± 15.0%) and box-squat 1RM (41.8% ± 26.3%) were still moderate and large respectively. The moderate change in box-squat 1RM resulted in a small difference between the supervised and unsupervised groups' long-term change (15.9%; ±13.2%). There was a small difference (2.4%; ±1.6%) between the groups' long-term changes in fat free mass. All other differences between the long-term changes (Pre-Post 2) were trivial or unclear.

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The Effect of Age

In the secondary analysis to determine the extent to which a change in age effects the changes because of training, there were no clear effects during both the conditioning and competition phases. However, results indicated that the younger subjects tended to show greater improvements.

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Training Variables

The mean attendance for the supervised group during the conditioning phase was 66%. The supervised group achieved moderately higher training volumes, loads, and frequencies for both the conditioning and competition phases than the unsupervised group (Table 4).

Table 4

Table 4

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Discussion

The effectiveness of a 15-week supervised off-season conditioning program was compared with an unsupervised program in provincial representative adolescent rugby union players. Supervised players realized greater improvements in strength, body composition, and acceleration compared to the common unsupervised approach. In addition, the persistence of the changes induced during the conditioning phase, determined after a 6-month unsupervised competition period, showed the physical and anthropometrical gains were reduced in the supervised group, resulting in only small long-term differences between the changes in box squat 1RM and fat-free mass. Finally, there were no clear effects of a change in age on the changes in physical characteristics as a result of training

During the 15-week conditioning phase, the differences in strength gains are comparable with those reported in other studies of similar subjects. For example, increases of 40 and 25.5% in 3RM squat and 29.8 and 15.3% in 1RM bench press in supervised and unsupervised junior rugby league players, respectively, have been reported after 12 weeks of resistance training (6). The participants of the unsupervised group in this study were provided with the same program; nonetheless, moderate differences occurred with the supervised group in training frequency, load and volume. It seems that supervision increased adherence to the program through the organization of a structured training environment. Furthermore, greater external motivation and competitiveness evident within-group training may have resulted in increased training intensity. The lifting of greater loads (expressed as kilograms lifted per set) has been shown within supervised sessions compared to unsupervised sessions, potentially resulting in the stimulation of a higher recruitment threshold of motor units (24,28).

Neural factors are primarily thought to be responsible for strength changes in adolescents (13); however, as an individual reaches postpubescence, the influence of hormonal factors upon muscle growth and development increases (22). The mean age of the subjects in this study was that typically associated with Tanner stage 5, indicating increases in the secretion of sex hormones (3). Furthermore, resistance training has shown to increase resting testosterone concentration in pubertal males, and may contribute to the anabolic process during the adolescent growth spurt (35). Therefore, the greater training loads performed by the supervised subjects may have been above the threshold to elicit a subsequent testosterone response and provide an enhanced milieu for the development of fat-free mass (22,39) and in combination with initial neural gains are likely to be the key contributors to the increases in strength in these players.

The trivial increase in mass over the period of the conditioning phase is in contrast to other studies that have found significant increases in mass after resistance and mixed conditioning training in similar subject populations (6,17). Alternatively, this study found small increases in the supervised group's fat-free mass after the conditioning phase, which may be attributed to the combination of the trivial increase in body mass and the substantially greater change in skinfold thickness compared with the unsupervised group. It could therefore be postulated that the greater training frequency, volume, and load within the supervised group may have contributed to a greater fat loss and thus a small increase in fat-free mass (24).

A greater increase in VJ height occurred for the supervised group compared with the unsupervised group over the period of the conditioning phase. The greater gains may be because of the greater adherence to the specific program, a lack of prior experience with structure plyometric training, and a lower initial performance level, all allowing scope for greater improvement. Moderate differences also occurred between the groups' changes in 10-m sprint time. The acceleration phase of the sprint is highly related to lower body power production (2); thus, in combination with the speed training, the plyometric training may have contributed to an increase in acceleration performance.

The differences between the changes in MFITS performance were inconsistent. During the conditioning phase, speed, anaerobic and aerobic conditioning were only prescribed once a week, because not all the players were familiar with specific training techniques and intensities. Therefore, the training may have been of insufficient frequency or volume to override the rapid growth and maturation process for minimal adaptation (24,36).

A novel aspect of this study was the long-term follow-up of physical performance to measure the longitudinal effects of the conditioning program. The follow-up was performed after a 6-month competition phase in which all the subjects were provided with an unsupervised training program that was prescribed to maintain the physical performance levels achieved during the conditioning phase. However, during the competition phase, strength tended to decline in the supervised group and continued to show trivial increases in the unsupervised group. There was an increase in overall frequency, volume, and load of training in the competition phase compared with the conditioning phase in both groups; however, the majority of time during this period is typically spent on team-based skill sessions and competition (1). Therefore, the frequency and volume of resistance and mixed conditioning training performed during the competition phase may have been lower than that performed during the conditioning phase and subsequently may have been insufficient to preserve the short-term gains made in physical characteristics. To reduce the diminishing effects of the unsupervised competition phase, it is recommended that supervision be maintained. This may provide stimulus for increased adherence and the ability to perform intensities and loads required to preserve the improvements in performance (6,24).

At the conclusion of the competition phase, both groups showed small increases in mass, indicating the increases may have partially been a result of maturation (37). However, greater increases in fat-free mass occurred longitudinally (Pre to Post 2) in the supervised group compared with the unsupervised group. These longitudinal changes suggest the development of fat-free mass may be accelerated in adolescent athletes with a greater training age (indicated by the differences in training frequency, volume, and load).

Previous studies into the detraining effect in adolescents have typically retested 8–12 weeks posttraining (9,20,37). The postintervention period in this study was therefore over twice as long as those previously investigated. Furthermore, the provision of training recommendations, as opposed to complete cessation of training, and the collection of training data have provided an insight into a follow-up more representative of an applied physical development program. This study has provided a framework for future research into the long-term persistence (or detraining) effects in adolescents, with even longer follow-ups over multiple years with multiple conditioning programs required to further understand the physical progression that may lead to elite performance.

The third aim of the study was to determine the effect of a change in age on the changes in physical performance as a result of training. Although results showed younger players tended to improve more, the differences were unclear. These trends may be indicative of younger players of lower training age and initial physical capacities, which create a greater propensity for improvement (10,16). Additionally, the training stimulus may have been insufficient to increase the physical capacities in the older players with greater training experience (17). Further research is therefore required to establish the effectiveness of training within specific adolescent age groups, to determine the age that elicits the greatest improvements.

A limitation of this study is the lack of a measure for maturation, limiting the ability to make evidence-based conclusions about the mechanisms responsible for the changes. Nonetheless, the mean age of the players at the commencement of the study (15.3 years) is that typically associated with Tanner stage 5, indicating near full physical maturity (3); thus, notable pubertal changes may not have been evident in some players. Furthermore, as players are grouped according to age within age group rugby union, the effect of age on the changes in physical performance as a result of training would have greater practicality for practitioners.

In summary, greater improvements in strength, anaerobic leg power (VJ and 10-m sprint time) and body composition were made in adolescent rugby union players who were supervised over a 15-week off-season physical conditioning program compared with a similar group that completed the same program but were not supervised. The greater increases may be attributed to greater training intensities achieved in a competitive group training environment. A longitudinal follow-up after an unsupervised 6-month competition phase showed reductions in physical and anthropometrical characteristics; however, changes in lower body strength and fat-free mass were still greater overall in the players that were initially supervised. The effect of age on the change in physical performance was unclear and requires further research to establish the efficacy of training within specific adolescent age groups. The results indicate the importance of a supervised development program, not only for safety within adolescent athletes but also for enhancing improvements in physical attributes (13).

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Practical Applications

It is common for off-season conditioning programs in adolescent rugby union players to be supplied without appropriate explanation or supervision. Coaches and administrators wanting to improve the physical performance of adolescent athletes should consider organized, structured, and supervised group training sessions to ensure improvements are made. If such organization does not occur, it is likely that changes in physical attributes may closely match those associated with normal maturation. Specifically, maintaining supervision during the competition phase may enable an enhanced state for subsequent off-season physical conditioning programs and greater long-term athletic development.

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Keywords:

supervised; unsupervised; strength training; physical development

© 2013 National Strength and Conditioning Association