The tackle is a physical contest between opposing players contending for territory and ball possession. During an 80 minute rugby union match, a player will physically engage in the tackle contest, whether as a ball-carrier or tackler, between 10 to 35 times depending on the position of the player (Deutsch et al., 2007; Quarrie and Hopkins, 2008). During a match, tight forwards (position numbers 1-5, who primarily compete in the set phases such scrums and lineouts) engage in the tackle approximately 10-25 times, loose forwards (position numbers 6-8, who mainly competes for possession of the ball at rucks and assist the tight forwards in set pieces) are involved in 25-35 tackles, inside backs (position numbers 9,10,12,13, whose key responsibility is to execute tactics and distribute the ball) competes in 20-25 tackles, and outside backs (position numbers 11,14,15, who are typically quicker and expected to run into open spaces to cross the advantage line and score points) engage in 10-15 tackles (Deutsch et al., 2007; Quarrie and Hopkins, 2008).
A player requires a high level of skill, physical tolerance and resistance to fatigue to repeatedly engage safely and effectively in the tackle, therefore understanding the physical demands of a tackle is important with many applications such as design and development of proper training drills and equipment, planning and management of training and recovery between training sessions and matches.
The biomechanics of injury risk can be explained by the event either resulting from an overload of the system’s tolerance levels, or a reduction in the system’s tolerance levels through micro trauma to a point where normal loads cannot be tolerated (McIntosh, 2005)
For the tackle, studies have shown a positive relationship between the number of tackles made during matches and markers of muscle damage (Smart et al., 2008; Takarada 2003). Also, repeated tackling decreases the amount of force produced by the tackler, which may be attributed to fatigue (Usman et al., 2011).
In rugby union and rugby league studies, the specific physical and technical requirements for safe and effective contact in the tackle have been highlight (summary of tackler below).
Based on this, we propose a theoretical model for the relationship between the number of tackles in which a player engages in (acute or chronic fatigue), magnitude of impact (energy load), markers of muscle damage (micro trauma) and how this relationship interacts with tackle injury risk (tolerance overload or reduction) and tackle performance (Hendricks and Lambert, 2014).
Players may have an upper limit for being able to endure repeated high energy impact tackles. If this upper limit is exceeded the risk of injury is substantially increased, and tackle performance is noticeably decreased (figure below). This upper limit is reached either through one or more very high-energy impact contact situations or, accumulates over a match or season following repetitive lower-energy impact situations. However, effective tackle skill training, proper physical conditioning, strength, power, equipment and attitude/motivation can offset this upper limit (McIntosh, 2005). For example, physically conditioned players with a high level of tackle skill may have the technical ability and physiological capacity to minimise the energy load on the body, thereby increasing their tolerance level for physical loads.
This paper was published in the Journal of Sport Science and Medicine. The full article can be found here http://www.jssm.org/letter.php?id=jssm-13-715.xml .