Changes in Sprint Momentum in Elite Rugby Union Players over a Three-Season Period

Abstract

The purpose of this study was to analyze the trend of sprint momentum over three consecutive seasons in elite rugby union players, to assess how body mass and sprinting speed affected changes in momentum, and to determine the impact of between-season changes in momentum on a selection of technical/tactical match performance indicators. The body mass, 10-m sprinting speed, and momentum of n = 37 elite rugby union players (age: 25.9 ± 2.8 y; height: 186.5 ± 7.3 cm; 22 forwards and 15 backs) were assessed over three consecutive seasons (2018–2021). Linear mixed-effects models were used to examine the impact of between-season changes in body mass and speed on momentum, and of body mass, speed, and momentum on technical indicators. Increased speed and body mass led to higher momentum (ES = 1.06–1.44). Speed changes improved effective carries, ineffective carries, carries, linebreaks, and offloads (ES = 0.48–1.17), while they reduced tackles (ES = −1.29). Changes in body mass reduced tackles (ES = −0.22) and improved effective carries (ES = 0.89) and carries (ES = 0.75). Changes in momentum reduced tackles (ES = −0.26) and ineffective contests (ES = −0.27), and improved offloads (ES = 0.61), effective carries (ES = 0.59), and carries (ES = 0.51). In conclusion, between-season improvements of momentum are achievable in elite rugby players, and, together with changes in speed and/or body mass, can have an impact on the technical/tactical performance during match play.

1. Introduction

Rugby union is a team sport that involves intermittent physical efforts, with frequent physical contacts and wrestling phases [1]. Achieving a high-level performance in rugby union requires the ability to sprint, as well as to accelerate and decelerate quickly [2,3,4]. The ability to accelerate, or the rate of change in speed, is considered more fundamental to success in team sports than maximum velocity [5]. Smart et al. [6] found significant correlations between players’ sprinting speed and technical/tactical performance indicators such as linebreaks and tries scored. A high sprinting speed allows players to be more difficult to tackle by opponents, while providing an advantage in making a tackle in the defensive phase [7]. Generally, backs are faster than forwards, particularly over distances of 30–40 m [8], and, between the 15th and 35th meter of a sprint, they can reach sprinting speeds comparable to those of competitive sprinters [4].

A large body size has been identified as a crucial factor for success in rugby union [9,10]. Over the past 35 years, the physical characteristics of rugby union players have shown an evident trend to increase [1,10,11,12,13,14,15,16,17,18,19]. Previous evidence suggests that the most successful teams in Rugby World Cups from 1987 to 2007 had the heaviest forwards [10] and the highest average team body mass [9]. Moreover, higher body mass in forwards correlates with increased force production during scrums [20,21] and tackles [22]. Forwards are also the players more involved in contacts in elite-level rugby, thanks to their greater body mass as compared to backs [4,23,24].

Another important physical characteristic of rugby players, especially in relation to tackles and collisions, is sprint momentum, that is, the product of a player’s sprinting velocity and body mass [25]. Momentum was observed to discriminate rugby union players of different competitive levels [16,19,26,27,28,29,30]. Forwards, despite exhibiting lower sprinting speeds than backs, show higher momentum thanks to greater body mass [17]. Previous authors also reported relationships between momentum and technical/tactical performance. Cunningham et al. [31] analyzed the correlations between physical test results and individual players’ key performance indicators measured during rugby union matches, observing large correlations between momentum and both dominant collisions (r = 0.862) and offloads (r = 0.776) performed by backs. Furthermore, in international female rugby union players, Woodhouse et al. [32] observed that momentum was associated with carries and tackles relative to time in forwards.

Since high body mass might be counterproductive to achieving a high running speed in a rugby union player, an optimal combination of body mass and sprinting speed is likely a key factor to maximize the momentum. At present, the interrelationships between short- and long-term changes in sprinting speed, body mass, and momentum, and the impact of these changes on a competitive performance in elite rugby union, have not been fully elucidated. Some authors have examined variations of fitness characteristics, including momentum, in rugby union across one season, reporting changes in sprint speed and momentum during the season in young players [31,32,33]. Instead, little has been investigated about longer term changes in momentum. To our knowledge, the only study performed over multiple seasons was conducted by Barr et al. [34], observing an increase of approximately 4.8% in body mass over a two-year period in junior players transitioning to the senior category. Noticeably, this change did not negatively affect the sprinting speed, leading therefore to an overall increased momentum [34].

There are no previous studies examining how long-term changes in momentum affect the individual technical/tactical match performance in rugby union players. To shed light on the magnitude and impact of long-term variations in momentum, the purpose of this study was to longitudinally analyze the body mass, sprinting speed, and momentum over three consecutive seasons in elite rugby union players. We analyzed the contributions of changes in body mass and sprinting speed to changes in momentum, and the relationships between inter-season changes in momentum and a selection of technical/tactical indicators.

2. Materials and Methods

2.1. Participants

Data were collected over a period of three seasons (2018/2019, 2019/2020, and 2020/2021) within a professional rugby team participating in the GUINNESS PRO 14 international championship. A total of 85 players were involved in the study over the examined seasons. Data of some players rostered in the examined team were excluded by the final analysis due to the occurrence of major injuries, or to the player having changed team during the study period. The final sample therefore included a total of 37 players (age: 25.9 ± 2.8 y; height: 186.5 ± 7.3 cm; 22 forwards and 15 backs), having played in official competitive matches for a total of at least 200 min in at least two out of the three examined seasons. Seven speed and body mass measurements (two to three per season) were performed for each player (approximately one every five months during the entire study period), and they were considered for further analysis. For all dependent and independent variables, the mean individual value calculated for a player over a season was taken as the data point for that player in that season. The study was approved by the University of Bologna Bioethics Committee (No. 0153636, 29 April 2025). Data were collected as part of players’ routine testing and monitoring, and all involved players provided consent for using their data for the purposes of this study.

2.2. Procedures

Sprint tests were carried out on an artificial turf field, over a 10 m distance. Sprint time was measured using Microgate Witty photocells (Microgate, Bolzano, Italy), with an accuracy of 0.01 s. Before the test, a warm-up of approximately 10 min, consisting of about 5 min of jogging, followed by dynamic flexibility exercises and two to four 20-m sprints at about 95% of maximum speed, was performed. The players started the test from a standing position with a standardized distance of 30 cm from the starting photocell, with a self-selected front foot. The best sprint time out of two trials was used to calculate the average velocity (expressed in m/s), which was used to calculate the momentum (mass in kg multiplied by speed in m/s, expressed in kg·m/s). Body mass measurements were taken in the morning in a fasting condition, on the same days in which sprint tests were performed, and measured to the nearest 0.1 kg with a Seca 769 scale (Seca Scale Corp, Munich, Germany).

A selection of match technical performance indicators collected in all official games played by the examined team over the three seasons included in the study (n = 67 games) were examined. The performance indicators were assessed as follows: tackles, sum of the number of effective tackles, neutral tackles, effective assisted tackles, ineffective assisted tackles, and recovery tackles; effective contest, the number of effective interventions at the breakdown; ineffective contest, the number of ineffective interventions at the breakdown; effective carries, the number of times a player brings the ball into contact, seeking advancement; ineffective carries, the number of times a player brings the ball into contact, looking for advancement; carries, given by the sum of effective and ineffective carrier; linebreaks, the number of times a player in possession of the ball breaks the defensive line; offload, the number of times the player made an effective pass while being tackled. The software Hudl Sportscode (Version 11, Hudl, Lincoln, NE, USA) was used to obtain the examined technical performance indicators.

For each indicator, to obtain seasonal values for each individual player, the total number of events performed by any player in all matches of a given season was taken and divided by the total playing time for that player in that season, and then multiplied by 80 to be normalized to an 80-min game, according to Cunningham et al. [31].

2.3. Statistical Analysis

All data are presented as the mean and the standard deviations. The effects of within-player seasonal changes in body mass and sprinting speed on changes in momentum were examined using linear mixed-effect models, with random intercept on individual players. Subsequently, linear mixed-effect models were run with momentum taken as a fixed factor with body mass and speed, and technical performance variables taken as dependent variables. For each model, the estimated effect size (ES) of the independent variable (fixed factor) on the dependent variable (outcome) was calculated with the following formula [35]:

$$ES={\displaystyle \frac{2·Estimated coefficient value·SD of the outcome variable}{SD of the Fixed Factor}}$$

(1)

Effect sizes were interpreted using the following thresholds: <0.20 = trivial, 0.20–0.59 = small, 0.60–1.19 = moderate, 1.20–1.99 = large, and ≥2.0 = very large [36]. All analyses were carried out for forward and backs separately. All analyses were performed using R software, version 4.3.1 (The R Foundation for Statistical Computing, Vienna, Austria).

3. Results

3.1. Body Mass, Sprinting Speed, and Momentum Across the Seasons

Table 1. Mean ± SD values of body mass, sprinting speed, and momentum across the three examined seasons.

	Season	Body Mass (kg)	Sprinting Speed (m/s)	Sprint Momentum (kg·m/s)
Forwards	18/19	111.8 ± 6.9	5.64 ± 0.21	629.6 ± 42.1
	19/20	111.0 ± 7.2	5.63 ± 0.24	624.4 ± 47.0
	20/21	109.9 ± 7.2	5.59 ± 0.20	614.5 ± 43.9
Backs	18/19	92.7 ± 7.1	5.79 ± 0.22	537.4 ± 47.4
	19/20	92.0 ± 5.8	5.84 ± 0.26	537.6 ± 42.6
	20/21	91.2 ± 5.4	5.78 ± 0.19	527.1 ± 36.9

shows the mean values of body mass, sprinting speed, and momentum for forwards and backs in the three examined seasons. For all of the examined variables, in both positional groups, the mean values were not significantly different between seasons (all p > 0.05).

3.2. Effects of Changes in Body Mass and Sprint Speed on Changes in Momentum

In backs, the linear mixed-effects modelling analysis revealed a significant effect of speed changes on momentum changes, with a 1 m/s improvement of speed leading to a momentum increase by 108.2 kg·m/s (95% CI 11.7–204.7 kg·m/s, p = 0.034, ES = 1.06, moderate). Moreover, in backs, a significant effect of body mass changes on momentum changes was observed, as follows: 1-kg increases of body mass induced a 6.1 kg·m/s (95% CI 3.64–8.57 kg·m/s, p = 0.002, ES = 1.44, large) increase in momentum. No significant effect of changes in players’ body mass on changes in sprinting speed was observed (p = 0.763).

In forwards, there was a significant effect of speed changes on momentum changes, with a 1 m/s increase in sprinting speed inducing a 99.5 kg·m/s increase in momentum (95% CI 7.25–191.72 kg·m/s, p = 0.036, ES = 1.39, large). Furthermore, a significant effect of changes in body mass on changes in momentum was observed. A 1-kg increase in body mass involved a 5.39 kg·m/s increased momentum (95% CI 3.76–7.01 kg·m/s, p < 0.001, ES = 1.37, large). No significant effect was observed between changes in players’ body mass and changes in sprinting speed (p = 0.808).

3.3. Effects of Changes in Body Mass, Speed, and Momentum on Changes in Technical Performance Indicators

In forwards, significant positive effects were detected of changes of sprinting speed on changes in effective carries (p = 0.001, ES = 0.85, moderate), ineffective carries (p = 0.032, ES = 0.54, small), carries (p = 0.001, ES = 0.83, moderate), linebreaks (p = 0.011, ES = 0. 48, small), and offloads (p = 0.005, ES = 1.17, moderate) (

Table 2. Relationships between physical performance and technical performance indicators for forward players over three seasons. Estimated coefficients with 95% confidence intervals and effect sizes are reported.

	Tackles		Effective Contest		Ineffective Contest		Effective Carries		Ineffective Carries		Carries		Linebreak		Offload
Predictors	Estimates CI 95%	ES	Estimates CI 95%	ES	Estimates CI 95%	ES	Estimates CI 95%	ES	Estimates CI 95%	ES	Estimates CI 95%	ES	Estimates CI 95%	ES	Estimates CI 95%	ES
Speed	0.031 (−4.560 to 4.621)	0.00	−0.925 (−2.039 to 0.189)	−0.11	−1.544 (−3.233 to 0.145)	0.09	4.535 * (2.076 to 6.995)	0.85	1.503 * (0.147 to 2.859)	0.54	6.030 * (2.849 to 9.212)	0.83	0.339 * (0.089 to 0.589)	0.48	1.720 * (0.590 to 2.851)	1.17
Body mass	−0.154 * (−0.257 to −0.050)	−0.22	−0.006 (−0.041 to 0.028)	−0.03	−0.037 (−0.088 to 0.013)	−0.14	−0.016 (−0.114 to 0.083)	−0.05	0.005 (−0.041 to 0.051)	0.03	−0.009 (−0.139 to 0.121)	−0.02	−0.001 (−0.010 to 0.088)	−0.03	0.013 (−0.029 to 0.055)	0.16
Momentum	−0.022 * (−0.040 to −0.005)	−0.26	−0.003 (−0.009 to 0.002)	−0.14	−0.009 * (−0.016 to −0.002)	−0.27	0.009 (−0.006 to 0.024)	0.24	0.005 (−0.002 to 0.012)	0.24	0.014 (−0.006 to 0.033)	0.28	0.001 (−0.001 to 0.002)	0.14	0.006 * (0.000 to 0.012)	0.61

* p < 0.05.

), while in backs, a significant negative effect of changes in sprinting speed was observed on changes in number of tackles (p = 0.002, ES = −1.29, large) (

Table 3. Relationships between physical performance and technical performance indicators for backs players over three seasons. Estimated coefficients with 95% confidence intervals and effect sizes are reported.

	Tackles		Effective Contest		Ineffective Contest		Effective Carries		Ineffective Carries		Carries		Linebreak		Offload
Predictors	Estimates CI 95%	ES	Estimates CI 95%	ES	Estimates CI 95%	ES	Estimates CI 95%	ES	Estimates CI 95%	ES	Estimates CI 95%	ES	Estimates CI 95%	ES	Estimates CI 95%	ES
Speed	−8.661 * (−13.284 to −4.037)	−1.29	−0.247 (−1.070 to 0.576)	−0.16	−0.355 (−1.132 to 0.421)	−0.21	0.428 (−3.093 to 3.949)	0.15	0.133 (−0.693 to 0.959)	0.07	0.590 (−3.088 to 4.269)	0.16	0.183 (−0.289 to 0.656)	0.23	0.656 (−0.440 to 1.752)	0.33
Body mass	−0.011 (−0.300 to 0.278)	−0.03	0.023 (−0.005 to 0.051)	0.30	0.017 (−0.013 to 0.046)	0.13	0.133 * (0.028 to 0.239)	0.89	0.009 (−0.020 to 0.037)	0.09	0.144 * (0.037 to 0.251)	0.75	0.009 (−0.008 to 0.027)	0.23	0.024 (−0.017 to 0.066)	0.24
Momentum	−0.026 (−0.063 to 0.010)	−0.41	0.002 (−0.002 to 0.006)	0.14	0.001 (−0.003 to 0.005)	0.06	0.016 * (0.000 to 0.032)	0.59	0.001 (−0.003 to 0.006)	0.08	0.018 * (0.002 to 0.034)	0.51	0.002 (−0.001 to 0.004)	0.22	0.005 (−0.001 to 0.010)	0.26

* p < 0.05.

). Body mass changes, in forwards, had an effect on the changes in number of tackles (p = 0.006, ES = −0.22, small) (Table 2), while in backs it had an effect on changes in effective carries (p = 0.018, ES = 0.89, moderate) and on changes in numbers of carries (p = 0.013, ES = 0.75, moderate). Some effects were detected of changes in momentum on changes in performance indicators. Changes in tackles (p = 0.016, ES = −0.26, small), ineffective contests (p = 0.019, ES = −0.27, small), and offloads (p = 0.048, ES = 0.61, moderate) were, respectively, observed to be associated with changes in momentum in forwards, while in backs changes in momentum affected changes in effective carries (p = 0.048, ES = 0.59, moderate) and of carries (p = 0.032, ES = 0.51, moderate).

4. Discussion

The main purpose of this study was to analyze the impact of within-player seasonal changes in sprinting speed and body mass on momentum, and of speed, body mass, and momentum on indicators of technical performance measured during official games in elite professional rugby players over three consecutive seasons. Taken together, the findings show that changes in body mass have a slightly higher impact than changes in sprinting speed on changes in momentum in forward, whereas in backs both changes in speed and body mass have large effects on changes in momentum. Moreover, increases in body mass do not affect sprinting speed in the range of observed changes. Various effects, ranging from small to large, were also observed of changes in speed, body mass, and momentum on match technical performance indicators in both forwards and backs.

The present findings suggest that an effective way to increase a player’s momentum would be to increase their body mass, since it is not associated with a decrease in sprint speed. These observations are in agreement with previous findings related to junior players transitioning to the senior category, demonstrating that increases of players’ body mass have an impact on momentum without negatively affecting sprinting speed [34]. Indeed, while speed performance can be reached very early by athletes in contact sports, momentum can continue to increase as athletes increase their muscle mass. Younger athletes have greater opportunities for improving physical capacities, especially in terms of speed, compared to senior players that are much closer to exhausting their potential [34,36]. Noticeably, despite the average body mass, sprint speed and momentum were almost unchanged during the three-year study period, and some individual players showed remarkable variations. Specifically, in backs, the range of changes between consecutive seasons were −5.5 to +7.1% for body mass, −4.7 to +5.9% for speed, and −5.7 to +4.8% for momentum, while in forwards they were −3.8 to +5.5% for body mass, −3.8 to +6.0% for speed, and −6.7% to +7.5% for momentum. The study used real-world data collected in an elite competitive rugby union team, where the players performed habitual training across the competitive seasons, and it was beyond the purpose of this study to investigate the effects of specific training strategies on body mass, sprint speed, and momentum values. Nevertheless, the observed changes lead us to suppose that, even in senior players, there can be long-term (between-season) improvements in sprinting speed and increases in body mass, which can be pursued if the aim is to improve momentum.

Another purpose of this study was to investigate the impact of between-season changes in speed, body mass, and momentum on changes in technical performance during official games played. Sprinting speed changes showed effects for both forwards and backs. Effective carries, ineffective carries, carries, linebreaks, and offloads were all positively impacted by running speed changes in forwards, while the only (negative) significant effect observed for backs was the number of tackles (−1.29). These findings are partially in agreement with previous research showing that carries have a relationship with sprinting speed in both forwards and backs [7,37]. Furthermore, these results agree with previous findings by Smart et al. [6], who reported relationships between speed and linebreaks, as well as numbers of tries scored. Moreover, the heaviest players were observed to be more efficient in carrying the ball during offensive actions, but higher body mass was not associated with increased tackling performance [17,22]. In agreement with this, in the present study, body mass changes were associated only with changes in the number of tackles for forwards, and were not related to changes in any performance variables for backs. Momentum changes were found to affect the numbers of tackles performed and ineffective contacts, and with effective carries and numbers of carries, for forwards and backs, respectively, all with small effects. These results are in partial agreement with findings by Cunningham et al. [31], who observed positive relationships between players’ momentum and dominant collisions and numbers of offloads performed by backs.

A limitation of the present study is that only the body mass of players was evaluated, instead of the lean mass or body composition. Separately examining the lean mass and the fat mass could provide further information, compared to considering body mass only. Another limitation is to have examined only one high-level elite team, whose training and playing activities can be influenced by player market and injury dynamics. A further limitation is that the analyses were not performed by position, but by positional group. Further research is needed to assess teams participating in leagues of different levels to understand the relationships between changes in physical and technical performance more in-depth. In conclusion, between-season improvements in momentum are detectable in elite rugby players. Together with changes in speed and/or body mass, changes in sprint momentum may have an impact on technical/tactical performance during elite rugby union competitions.