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Original Research

Long-Term Training-Induced Changes in Sprinting Speed and Sprint Momentum in Elite Rugby Union Players

Barr, Matthew J.1; Sheppard, Jeremy M.1; Gabbett, Tim J.2,3; Newton, Robert U.1

Author Information
Journal of Strength and Conditioning Research: October 2014 - Volume 28 - Issue 10 - p 2724-2731
doi: 10.1519/JSC.0000000000000364
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Abstract

Introduction

Speed is commonly considered to be a highly valuable ability in rugby union and a key component of a team's success (9). A notable difference between specialist sprinters competing in track and field and rugby players is the body mass. When examining historical data of the body types of elite sprinters, it would appear that there exists an optimal body mass for sprinters (26,27,29) that is not likely optimal for rugby union players (8). The mass differences between sprinters and rugby players are likely related to the various collisions in the game that favor heavy body mass (7,18). An indicator of the continued importance of size in rugby union has been the steady increase in body mass of players over the history of the game (16,22). The importance of both body mass and sprinting speed in rugby may mean that the combination of the 2, sprint momentum, is a more important determinant of success in rugby union. Sprint momentum, calculated by multiplying sprinting velocity with body mass, has previously been found to discriminate between performance levels of elite rugby league players (4), but there is currently a gap in the literature analyzing the importance of sprint momentum in elite rugby union players. Elite rugby union players might choose to play at a body mass that is not optimal for maximizing sprinting speed but optimizes sprint momentum. However, the relationships between sprinting speed, mass, and momentum and how they may discriminate between playing levels of elite rugby players are currently unclear.

Previous research that has examined long-term changes in strength and power in contact field-sport athletes such as rugby union (1), rugby league (2,3), and American football (12,15,24) players indicated that strength development can continue throughout a playing career. Long-term changes in the sprinting speed of American university football players, however, suggest that the development of speed is much more limited when compared with strength (15,24). It may be possible that speed peaks very early as a physical quality in contact field-sport athletes but sprint momentum continues to develop for a longer period of time as athletes continue to gain muscle mass (1). There are currently no published studies that have examined whether or not elite rugby union players improve sprint momentum and sprinting speed over several years of training.

The purpose of the study was to understand the development of the sprinting speed and sprint momentum in senior and junior international rugby players. Three different components of sprint momentum and sprinting speed were specifically examined. First, we examined whether speed or momentum could discriminate between senior and junior international rugby union players. Second, we examined whether or not junior rugby union players transitioning into senior rugby develop sprint momentum and speed at greater rates than senior rugby union players. Finally, we examined the relationship between sprinting speed, sprint momentum, and body mass. It was hypothesized that sprint momentum but not speed would discriminate senior and junior union players. It was hypothesized that junior players transitioning into senior rugby would improve sprint momentum at a greater rate than senior players and would close the sprint momentum gap over 2 years. It was also hypothesized that body mass would negatively affect sprinting speed but there would be an optimal body mass for maximizing sprint momentum.

Methods

Experimental Approach to the Problem

To understand how sprint momentum and sprinting speed are developed in elite rugby players, the study was divided into 2 parts. The first part consisted of a causal-comparative cross-sectional design and second part of the study was a longitudinal quasi-experimental design. The first part of the study consisted of determining sprinting velocity, sprint momentum, and body mass of 69 junior and senior international rugby players. The second part consisted of tracking the changes in body, sprinting speed, and sprint momentum of 28 international rugby union players over a 2-year period. Two-way and repeated-measure analyses of variance (ANOVAs) were used to calculate differences between the different conditions and groups. Correlations were also calculated between mass, sprint momentum, and sprinting velocity in part 1 and the changes in these qualities over 2 years in part 2.

Subjects

The participants in the first part of the analysis (height, 1.84 ± 0.1 m; body mass, 102.8 ± 11.9 kg; age, 26.2 ± 3.2 years) were 38 senior national team players (21 forwards and 17 backs) from the same national team (typically 11th–15th place in the International Rugby Board world rankings) and 31 under-20 national team players (17 forwards and 14 backs) also from the same country's national team (height, 1.84 ± 0.1 m; body mass, 93.2 ± 12.3 kg; age, 19.2 ± 0.9 years). The participants in the second part of the analysis were 12 (4 forwards and 8 backs) junior national team players (height, 1.85 ± 0.07 m; body mass, 92.2 ± 8.8 kg; age 18.9 ± 0.5 years) transitioning into senior rugby and 15 (6 forwards and 9 backs) senior national team players (height, 1.83 ± 0.06 m; body mass, 94.6 ± 8.6 kg; age, 24.1 ± 2.3 years). All of the junior players were playing under-20 national team players at the beginning of the study and had played senior international rugby (IRB test match or A match) by the end of the study. All of the participants involved in the study were training on a full-time basis at a national team training academy. Each of the participants was typically involved in approximately 8–12 weeks per year of national team duty, 24 weeks per year of club rugby, 12–16 weeks per year of preseason training, and 4 weeks of rest. Training during national team competition weeks involved 1–2 strength training sessions and 3–4 rugby practices per week. Training during club rugby competition weeks typically involved 2–3 strength training sessions, 1–2 speed training sessions, and 2–3 rugby practices per week. Training during preseason training typically involved 2–3 speed training session, 3–4 strength training sessions, and 1–2 rugby practices per week. Given the intense nature of rugby, each player was injured at some point of the study so that their training had to be modified, but no players were injured to an extent that long-term layoffs (>1 month) occurred. Each participant was following their own individualized training program, but typical sprint training sessions were based on the exercises listed in Table 1. Strength training sessions typically consisted of variations of the Olympic lifts, squats, pressing exercises, upper-body pulling exercises, plyometrics, and other exercises. Each session typically consisted of 4–6 exercises performed for 5–8 sets of 1–8 repetitions. Each participant gave written informed consent, and the study had Institutional Review Board approval.

Table 1
Table 1:
Typical speed exercises used during training (100–350 m per session total volume).

Procedures

Each of the players performed four 40-m sprints on an artificial field using a Brower (Brower Timing Systems, Draper, UT, USA) system with timing gates placed on 1 m high tripods at 0, 10, 30, and 40 m. The players began each sprint with their front foot beside a cone 0.75 m behind the first gate. The order of the trials was randomized for each subject to balance the possible effects of fatigue. Each subject completed at least 1 trial of each condition before their second round where they completed trials in the same order. A rest time of 4–5 minutes was given between each trial. The fastest 0- to 10- and 30- to 40-m splits were kept for analysis. The 0- to 10-m split is representative of acceleration ability, and the 30- to 40-m split is representative of maximal velocity (6). Velocity scores (m·s−1) were calculated for both of these splits by dividing the 10-m split by the time taken to complete the trial. The 0- to 10-m split was defined as initial sprint velocity (ISV) and the 30- to 40-m split as maximal sprint velocity (MSV). The mass of the athlete was multiplied by both velocity scores (kg·m−1·s−1) to obtain an initial sprint momentum (ISM) and maximal sprint momentum (MSM) score. Mass, height, and sum of 7 skinfolds (bicep, tricep, subscapular, abdominal, supraspinale, front thigh, and medial calf) of the athletes were tested using the protocol of the International Society for the Advancement of Kinanthropometry (23) by an ISAK-certified tester (level 2).

Statistical Analyses

Reliability for ISV and MSV was determined to be very reliable with intraclass correlations of r = 0.91 and r = 0.94. To compare mass, momentum, and velocity differences between under-20 and senior players in part 1, a 2-way (positional × age group) ANOVA was used. To compare changes in mass, momentum, and velocity differences between under-20 and senior players in part 2, a 2-way repeated (time × age group) ANOVA was used. The level of significance was set at p ≤ 0.05. If a significant F value was found, then a Tukey's post hoc test was used to determine the source of these differences. Complete data sets of sum of 7 skinfolds were only available for the beginning of the 2-year period and the end of the 2-year period, so a paired t-test was used to compare them. Pearson's correlations were calculated to characterize the relationship between sprinting velocity, sprint momentum, and mass. To characterize the differences between groups, Cohen's d effect sizes were calculated. The following classification system was used to determine the magnitude (13) of Cohen's d effect sizes, effect sizes were considered trivial for being <0.2, small for ≥0.2 and <0.6, moderate for ≥0.6 and <1.2, large for ≥1.2 and <2.0, and very large for >2.0. An alpha of p ≤ 0.05 was set for level of significance for ANOVAs. All statistical analyses were conducted using XLSTAT (Addinsoft, NY, USA) software.

Results

In part 1, moderate differences in ISM (mean difference: 49 kg·m−1·s−1, p < 0.0001, Cohen's d = 0.81) and MSM (79 kg·m−1·s−1, p < 0.0001, d = 0.95) were found between senior and under-20 players. Trivial differences in ISV (p = 0.426, d = 0.17) and MSV (0.05 m·s−1, p = 0.71, d = 0.09) were found between senior and under-20 players. Very large correlations were found between mass and MSM (r = 0.84) as well mass and ISM (r = 0.92). Large correlations were found between ISV (r = −0.52) and MSV (r = −0.68). In part 2, no significant differences were detected between the senior and junior groups at any of the time points. The junior group made large improvements in MSM (mean change: 86 kg·m−1·s−1, p = 0.03, d = 1.15) and MSV (0.5 m·s−1, p = 0.02, d = 1.09) and moderate increases in ISM (44 kg·m−1·s−1, p = 0.04, d = 0.96) and ISV (0.2 m·s−1, p = 0.13, d = 0.73) over the 2 years. The changes in the senior group were considerably lower with moderate improvements in ISV (0.18 m·s−1, p = 0.02, d = 0.79), MSV (0.27 m·s−1, p = 0.24, d = 0.68), ISM (26 kg·m−1·s−1, p = 0.36, d = 0.54), and MSM (37 kg·m−1·s−1, p = 0.42, d = 0.50). Trivial differences (p = 0.92, d = 0.02) were found for changes in sum of 7 skinfolds between the pretesting period (65.8 ± 20.0 mm) and end of the 2-year period (66.3 ± 18.4 mm) in the combined group of junior and senior players (Tables 2–5; Figures 1–3).

Table 2
Table 2:
Differences in maximal sprint momentum, initial sprint momentum, maximal sprint velocity, and initial sprint velocity between senior and under-20 national team rugby forwards and backs.*
Table 3
Table 3:
Two year changes in mass, maximal sprint momentum, initial sprint momentum, maximal sprint velocity, and initial sprint velocity of senior and junior national team players transitioning into senior international rugby.*
Table 4
Table 4:
Pearson's correlations between momentum, velocity and mass in elite rugby players (n = 69).
Table 5
Table 5:
Pearson's correlations between changes in momentum, velocity and mass in elite rugby players over 2 years (n = 27).
Figure 1
Figure 1:
Differences in maximal sprint momentum (A), initial sprint momentum (B), maximal sprint velocity (C), and initial sprint (D) between senior and under-20 national team rugby forwards and backs. Senior group results are in black and under-20 players are in white. Asterisk denotes a significant difference (p ≤ 0.05) between senior and under-20 players. Dashed line denotes a significant difference (p ≤ 0.05) between forwards and backs.
Figure 2
Figure 2:
Two-year changes in mass (E), initial sprint velocity (D), maximal sprint velocity (C), initial sprint momentum (B), and maximal sprint momentum (A) of senior international rugby players and junior rugby players transitioning into senior international rugby. Senior players are denoted with solid bars and junior players transitioning into senior rugby are denoted with dashed bars. Error bars denote SD.
Figure 3
Figure 3:
Relationship between body mass and maximal sprint momentum (solid diamonds, top graph), initial sprint momentum (open circles, top graph), maximal sprint velocity (solid diamonds, bottom graph), and initial sprint velocity (open circles, bottom graph).

Discussion

The similarity of sprinting speed but significant difference of mass and momentum between senior and junior players in part 1 are consistent with a previously reported comparison of elite junior and senior players (10) that showed differences in body mass but not sprinting speed. The differences in mass between forwards (∼11 kg) and backs (∼8 kg) in part 1 could indicate that this is a normal amount of mass for junior players to put on as they progress into senior rugby and they do so without increasing sprinting speed. The differences in mass and momentum between the 2 age groups could also have been skewed by junior players who do not have the frame to carry large amounts of muscle mass and will not progress onto senior rugby. Height was equivalent between the 2 groups but skeletal dimensions were not measured so this is unknown. The junior players transitioning into senior rugby did put on mass over 2 years (4.4 kg) but it was much less than the differences between the 2 age groups in part 1.

The cross-sectional data from part 1 and the study of Hansen et al. (10) might cause coaches to conclude that speed is not improved past 19 years of age because there was no difference in speed between juniors and seniors. The data from part 2 of this study provide strong evidence that sprinting speed, sprint momentum, and mass can all be improved with senior and junior players but junior players do have a greater window of adaptation for developing these qualities. No differences at any of the time points were detected between the senior and junior groups but the differences in effect sizes of the groups show that the senior group was near exhausting their potential of speed and sprint momentum improvement. The junior group made greater changes in the different sprint qualities when compared with the senior group with the exception of ISV that was similar between the 2 groups (Table 3; Figure 2). These results show that large changes can be made in all of the different sprint qualities in junior players transitioning into senior rugby but the greatest changes can be made in MSM. The strength and speed training (Table 1) that all of the players undertook likely influenced the athletes' ability to increase sprinting speed and sprint momentum. The heavy squatting, pressing, and pulling exercises were likely helpful for increasing body mass (1,5), and the emphasis on power exercises (5,11,19,25) and sprint-specific training methods (17,28) were likely able to improve the ability to develop the large but brief forces (14,29) necessary for maximal speed sprinting. Improving sprint momentum is likely somewhat more complex than improving sprinting speed as there are simultaneous goals of increasing muscle mass but improving the ability to develop mass-specific forces in a briefer time period. It could be inferred from the improvements in sprint momentum and sprinting velocity that the strength and speed exercises used in this study, at least in junior players, are successful for this. The smaller improvements in senior players in the first year and negligible improvements in the second year may indicate a few different things. It may indicate that the technique and neuromuscular changes that can improve sprinting speed (20) were possibly exhausted in these athletes, and no further improvements could be made. Alternatively, the exercises or training frequencies were inadequate for improving performance. Another possibility is that the extensive training background of the athletes may mean that larger gains must be made in training activities to observe noteworthy gains in sprint activities.

A hypothesis of this study was that body mass would negatively affect sprinting speed. Body mass in part 1 was found to have a stronger negative association with MSV (r = −0.68) than with ISV (r = −0.52) (Figure 3). This finding is in agreement with research that suggests that MSV is limited by the ability to develop mass-specific forces in a briefer period of time (30), but higher body masses negatively affect the ability to develop mass-specific forces (21). The mass of the players in part 1 of this study (101.7 ± 11.8 kg) was considerably higher than the narrow range of body masses (77.0 ± 6.6 kg) reported by Uth (26). If speed was the only key physical ability for rugby players, then the implication would be that players should focus on lowering their body mass. The small changes in mass of the players over 2 years, however, did not negatively affect their sprinting velocity (Tables 3 and 5), so these results would support the idea that small gains in mass can be made without compromising improvements in sprinting speed. The correlations between the changes in mass with ISV (r = −0.02) and MSV (r = −0.07) over 2 years were very weak, which means that it is a safe assumption that increasing muscle mass to increase sprint momentum will not negatively affect sprinting velocity.

Given the number and intensity of collisions in rugby, maximizing sprint momentum likely needs be a key focus for training rugby players. In part 1, a very large correlation (Figure 3) was found between mass and both ISM (r = 0.92) and MSM (r = 0.84). It could be concluded from this that there is a compromise between maximizing sprint momentum and maximizing sprinting velocity as mass positively affects one (momentum) and negatively affects the other (velocity). The longitudinal data from Table 5 indicate that increasing mass has the greatest effect on increasing ISM (r = 0.80) and MSM (r = 0.73), but the increases in momentum also correspond to increases in ISV (r = 0.59) and MSV (r = 0.63). This means that the sprint momentum of elite rugby players can be increased by developing both body mass and sprinting speed. It may be possible that excessively increasing body mass will negatively affect sprinting speed but positively affect sprint momentum. Maximizing momentum through increasing body mass is likely important for players whose position involves ball carrying in situations where contact is unavoidable (tight 5 players, etc.), and maximizing sprinting speed by minimizing body mass is more important for players where carrying a ball at maximal speed is normal and contact is somewhat avoidable (wingers, etc.). This is supported by the fact that in part 1, forwards were slower for both ISV (mean difference: −0.28 m·s−1, p < 0.0001, d = 1.04) and MSV (−0.72 m·s−1, p < 0.0001, d = 1.4) but had higher levels of ISM (77 kg·m−1·s−1, p < 0.0001, d = 1.68) and MSM (88 kg·m−1·s−1, p < 0.0001, d = 1.45). The relationship between sprint momentum, body mass, and sprint velocity would suggest that positional ideal standards should be set and all 3 scores need to be considered when testing.

Given the importance of sprint momentum for rugby union, it would be beneficial for future research to assess the impact of players improving sprint momentum. It would be worthwhile to know if the ability to gain mass and increase sprint momentum differentiates players who are successful in advancing to higher levels of competition from their peers who do not progress to higher levels. Additionally, it would also be interesting to know whether an increase in sprint momentum leads to individual improvements in performance during games. For instance, an off-season training program resulting in an increase in sprint momentum could lead to more effective tackles while on defence and more tackle breaks (31) while on offense during the following season.

Practical Applications

Improving sprint momentum is likely a key component of physical preparation for rugby. Monitoring sprint momentum, and not just sprinting speed, should be a key focus for strength and conditioning coaches working with rugby players. Measuring sprint times with 10-m splits allows for coaches to consider both sprinting speed and sprint momentum qualities. This allows for coaches to track meaningful changes in performance while considering improvements in both lean body mass and sprinting speed. Positional standards for both momentum and speed should be developed and be set as targets when planning training programs. The window for adaptation in developing sprint momentum and sprinting speed is likely greater for players in their late teens and early 20s when compared with players in their mid-to-late 20s. Developing sprint momentum and sprinting speed should, thus, be a key focus with this age group. To increase sprint momentum, strength training likely needs to consist of exercises that will increase both muscular hypertrophy and power. These exercises also need to be combined with different sprint training methods, so an increase in body mass does not negatively affect sprinting speed.

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Keywords:

acceleration; maximal sprint velocity; long-term athlete development

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