# Changes in Sprint Momentum in Elite Rugby Union Players over a Three-Season Period
## 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 [PERSON] 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.