March 9, 2016

Overview of the latest research on the tackle in youth rugby

by Nicholas Burger

The tackle is an intrinsic part of rugby union. It is a display of physical strength and technical proficiency and is a skill that is required across all playing positions. It is also responsible for a large proportion of injuries in the sport. Research pertinent to the tackle in rugby union and associated aspects of safety and performance has been conducted predominantly in senior playing cohorts (Quarrie and Hopkins, 2008; McIntosh et al., 2010; Fuller et al., 2010) and less is known about youth levels of the game. The following article highlights current literature available regarding tackle safety, injury and performance in rugby union, particularly at the youth level.

Injury epidemiology

Injury rates in youth rugby union are high in comparison to other team sports, and this is primarily due to the tackle. The incidence rate in under-13 South Africa rugby is 50.0 injuries per 1000 exposure-hours (Burger et al., 2014). It is important to note that the tackle is the most frequently occurring contact event in rugby and, therefore, may not carry a high propensity to cause injury (number of injuries per event) in comparison to other less frequent forms of contact, for example the scrum. However, further research at the youth level is required to determine this.

Between 2008-2011, eight tackle-related injuries in South Africa resulted in a permanent ASCI (acute spinal cord injury) (Brown et al., 2013). Only one of these injuries occurred to a junior (under-9 to under-17) rugby union player.

Injury surveillance was conducted for under-13, under-16, and under-18 age groups over 3 years at the South African Rugby Union Youth Week tournaments, with 7216 players participating in 531 matches between 2011 and 2014. Across all 3 age groups over the 4 monitored years, one hundred and eight concussion events were recorded at a rate of 6.8/1000 player-match-hours (95% CI, 5.5-8.1). Of the one hundred and eight concussions, 62% occurred in the tackle (McFie et al, 2016). Further analysis of the concussion injury mechanism in the undr-18 cohort found that players who failed to execute certain techniques substantially increased the potential for concussion (Hendricks et al. 2015).

Technique

Recent research has shown that under-18 rugby union players who demonstrate poor tackle technique (for tackling and ball-carrying) are at a greater risk of being injured (Figure 1 and Figure 2, Burger et al., 2016). This is the first time this aspect of tackling has been studied in youth level rugby union. Findings from this research advocate and add to the current coaching guidelines on safe tackle technique, which is also the most effective technique (Hendricks et al., 2014).

Figure 1: Ball-carry technique proficiency scores comparing injury vs. non-injury for front-on and side-on tackles.

Figure 2: Tackler proficiency scores comparing injury vs. non-injury for front-on and side-on tackles.

A study comparing the tackle-related injury rates and characteristics of varying levels of rugby union in Australia observed that junior players (under-15) were significantly less like likely to be injured in a tackle when compared to senior professional players (McIntosh et al., 2010). This finding may be attributed to the lower playing intensity and impact forces that occur in youth rugby union.

It is noteworthy that a study in youth ice hockey found that under-13 players who had previously participated in non-contact (no body-checking) forms of the game were at a higher risk of being injured during contact in comparison to players who had previously experienced body-checking (Emery et al., 2011). This increase in injury risk may be attributed to a lack of physical preparedness and technical proficiency (Hendricks et al., 2015).

Player conditioning

Repetitive tackling and contact load may result in acute and chronic fatigue which may predispose rugby players to injury (Hendricks and Lambert, 2014). Physiological and anthropometric conditioning are prerequisite to participating in rugby union and go hand-in-hand with well-developed technical proficiency (Gabbett, 2008; Hendricks and Lambert, 2014).

Player knowledge, attitude and behaviour

Research has shown that junior rugby players tend to place dominating the tackle as a priority over safety for themselves or their opponent (Hendricks et al, 2012). Junior players should not only be physically conditioned for rugby and contact situations but it is clear that these players may also require psychological conditioning informing them of the benefits of performing safe tackle technique (which may also be the most beneficial towards a successful performance outcome). This may be achieved through educational safety programmes.

Guidelines for Tackle Skill Development

In 2010, Hendricks and Lambert (2010) proposed guidelines to development tackle technique based on the literature available at the time.

Safety and educational programmes

There are numerous rugby safety programmes available that disseminate educational guidelines for coaches, parents, players and medical professionals. These programmes (BokSmart, RugbySmart, World Rugby) include specific information regarding safety during contact and tackles, and provide advice to ensure that players are physically conditioned and prepared for participation (Quarrie et al., 2007; Brown et al., 2015).

In addition to the research…

Legislation

The tackle is a highly dynamic and open phase of play. As a result, it is more difficult to regulate and control in comparison to set-piece plays including the scrum and line-out. However, over the years, World Rugby has developed and implemented game laws to combat dangerous behaviour during tackles. These laws state that a player ‘a player must not tackle (or try to tackle) an opponent above the line of the shoulders even if the tackle starts below the line of the shoulders’ (Law 10.4e) and ‘a player must not charge or knock down an opponent carrying the ball without trying to grasp that player (Law 10.4g) (World Rugby Law 10). These laws apply to all levels of play.

Conclusion

From the above it is evident that a concerted effort is being made to make contact situations, particularly the tackle, safer for participants at all levels of rugby union. While injury surveillance forms a crucial part of injury epidemiology research, it alone cannot guide injury prevention solutions. It is important to also identify the circumstances and factors which contribute to the manifestation of injuries. These factors are often modifiable and may be controlled to reduce the burden and incidence of injury.

Youth rugby union players should be physically and mentally conditioned to cope with contact, safe and effective tackle technique should be emphasised during training sessions, referees and match officials must ensure that the laws of the game pertinent to contact and foul play are stringently adhered to, and safety and educational guidelines must be distributed widely amongst all stakeholders in youth rugby union.

Nicholas Burger is a PhD candidate at the Division of Exercise Science and Sports Medicine (ESSM), University of Cape Town. He is investigating the mechanisms of injuries during tackles and novel methods to reduce the incidence of these injuries.

References

Brown JC, Lambert MI, Verhagen E, et al. The incidence of rugby-related catastrophic injuries (including cardiac events) in South Africa from 2008 to 2011: a cohort study. BMJ Open 2013;3(2):e002475.

Brown JC, Verhagen E, Knol D, et al. The effectiveness of the nationwide BokSmart rugby injury prevention program on catastrophic injury rates. Scandinavian Journal of Medicine and Science in Sports 2015;doi: 10.1111/sms.12414.

Burger N, Lambert MI, Viljoen W, et al. Tackle-related injury rates and nature of injuries in South African Youth Week tournament rugby union players (under-13 to under-18): an observational cohort study. BMJ Open 2014;4:e005556.

Burger N, Lambert MI, Viljoen W, et al. Tackle technique and tackle-related injuries in high-level South African Rugby Union under-18 players: real-match video analysis. British Journal of Sports Medicine 0:1-8, 2016.

Emery C, Kang J, Shrier I, et al. Risk of injury associated with bodychecking experience among youth hockey players. Canadian Medical Association Journal2011;183(11):1249-1256.

Fuller CW, Ashton T, Brooks JHM, et al. Injury risks associated with tackling in rugby union. British Journal of Sports Medicine 2010;44:159–167.

Gabbett TJ. Influence of fatigue on tackling technique in rugby league players. Journal of Strength and Conditioning Research 2008;23:540–548.

Hendricks S, Jordaan E, Lambert MI. Attitude and behaviour of junior rugby union players towards tackling during training and match play. Safety Science 2012;50:266–284.

Hendricks S, Matthews B, Roode B, Lambert M. Tackler characteristics associated with tackle performance in rugby union. European journal of sport science. 2014;14:753-762.

Hendricks S, Lambert M. Tackling in rugby: Coaching strategies for effective technique and injury prevention. International Journal of Sports Science and Coaching. 2010 1;1:117-36.

Hendricks S, Lambert MI. Theoretical Model Describing the Relationship between the Number of Tackles in Which A Player Engages, Tackle Injury Risk and Tackle Performance. Journal of Sports Science and Medicine 2014;13:715-717.

Hendricks S, O’connor S, Lambert M, Brown J, Burger N, Mc Fie S, Readhead C, Viljoen W. Contact technique and concussions in the South African under-18 Coca-Cola Craven Week Rugby tournament. European journal of sport science. 2015;15:557-64.

Mc Fie S, Brown J, Hendricks S, Posthumus M, Readhead C, Lambert M, September AV, Viljoen W. Incidence and Factors Associated With Concussion Injuries at the 2011 to 2014 South African Rugby Union Youth Week Tournaments. Clinical Journal of Sport Medicine. 2016 doi: 10.1097/JSM.0000000000000276.

McIntosh AS, Savage TN, McCrory P, et al. Tackle characteristics and injury in a cross section of rugby union football. Medicine and Science in Sports and Exercise 2010;42:977–984.

Quarrie KL, Gianotti SM, Hopkins WG, et al. Effect of nationwide injury prevention programme on serious spinal injuries in New Zealand rugby union: ecological study. BMJ 2007;334:1150.

Quarrie KL, Hopkins WG. Tackle injuries in professional rugby union. American Journal of Sports Medicine 2008;36:1705–1716.

March 4, 2016

Managing the acute : chronic workload ratio among team sport athletes

Managing the individual in a team sport environment is one of the greatest challenges but one of the most crucial aspects to the collective success of the team. Training and performance share a complex relationship, which is based on several factors, many of which are unique to the specific individual and the performance task. Therefore, athlete monitoring has become a popular trend among strength and conditioning coaches¹.

Monitoring training loads is one of the simplest ways to determine the athlete’s response to the training stress over a period of a time. By monitoring what an athlete has performed in a week (Acute workload) compared to what he has been prepared for (Chronic workload), the strength and conditioning coach can begin to build trends in predicting injury risk. Predicting and ultimately preventing injury is the “Holy Grail” in athlete performance. The Chronic workload can be determined as an athlete’s state of fitness, whereas the acute workload can be determined as the athlete’s state of fatigue². The difference between the positive function of fitness and the negative function of fatigue produces either a positive (where the chronic workload is above the acute workload) or a negative (where the chronic workload is below the acute workload) training-stress balance. The assumption is that physical preparedness grows as chronic workload outweighs acute workload² – suggesting that as fitness improves and fatigue is reduced, the performance of the athlete should improve. However, if acute workload outweighs chronic workload, the athlete is at an increased risk of injury – especially in the week following a negative training-stress balance.

load

The above graph shows an example of a training phase depicting chronic workload, acute workload and daily workload. This is indicative of a positive training-stress balance as the athlete’s chronic workload outweighs the acute workload over a period of time.

It is important to note that a sudden spike in daily training load will increase the athlete’s acute workload while decreasing the chronic workload², potentially leading to a negative training-stress balance and increased risk of injury in the 1 week following.

A more recent calculation in the form of a ratio provides defined thresholds with quick and easy feedback. The acute:chronic workload ratio indicates that a player is less resistant to injury when subjected to spikes in acute workload, which equates to very-high acute:chronic ratios ~ 1.5³.

THE CHRONIC:ACUTE TRAINING LOAD RATIO

In the current week, a very high acute:chronic workload (>2.11) in combination with a very high acute workload is associated with an increased risk of injury by up to 6.9 times as well as demonstrating a 10 fold increase in injury risk in the subsequent week³.

The acute:chronic workload ratio needs to be analysed in combination. A high chronic workload combined with moderate, and moderate – high workload ratios had a smaller risk of injury than a low chronic workload combined with several acute:chronic workload ratios³. (Additional Reading recommended; Training injury paradox: should athletes be training smarter or harder?; Gabbett, T; BJSM)

It is suggested that monitoring acute:chronic workloads be mainstream practice in elite sport in order to better predict the onset of injury and therefore prevent rather than react. For the most practical application, it is best to monitor the acute to chronic workload ratio during the current week and as an average over two weeks relative to either a high or low chronic workload.

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REFERENCES

Joyce D, Lewindon D. High Performance Training for Sports. Human Kinetics; 2014.
Hulin BT, Gabbett TJ, Blanch P, Chapman P, Bailey D, Orchard JW. Spikes in acute workload are associated with increased injury risk in elite cricket fast bowlers. Br J Sports Med. 2014;48(8):708-12.
Hulin BT, Gabbett TJ, Lawson DW, Caputi P, Sampson J a. The acute:chronic workload ratio predicts injury: high chronic workload may decrease injury risk in elite rugby league players. Br J Sports Med. 2015;33:1-7.

February 4, 2016

Understanding Neuromuscular Adaptations in High Performance Athletes:

Part 3: Testing & evaluating special strength:

With a basic overview and understanding of various neuromuscular adaptations to training, the next aspect which we will look at, is the evaluation of our athlete’s ability to express power as well as what best practice is to improve it.

Samozini et al, recently published a study on an iPhone app that allows you to not only determine jump height through flight time but also build a force-velocity profile on your athletes (see figure 1).

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Apps like this are very useful, as they are cost effective, portable, valid and reliable – see link to open source;

(paperhttps://www.researchgate.net/publication/270286306_The_validity_and_reliability_of_an_iPhone_app_for_measuring_vertical_jump_performance)

They allow strength and conditioning specialist to conduct scientific analyses on their athletes with ease, they allow strength and conditioning specialist to conduct scientific analyses on their athletes with ease, and in-turn they gather valuable information from it to allow for better program prescription.

But before we move on, let me introduce you to a few terms that are synonymous with explosive power:

Starting Strength: The muscles ability to produce force at the start of the contraction before any external movement occurs.

Acceleration Strength: The ability to produce Fmax force as quickly as possible at the start of and isometric or concentric contraction.

Index of Explosive Strength (IES): Is an expression of the of the athletes ability to produce maximal force in the shortest time period. IES = Fmax / Tmax

Rate of Force Development (RFD): Rate of rise of contractile force at the onset of a muscle contraction. RFD = Fmax (A) – Fmin (B)/ Time from A – B

Reactivity Coefficient (RC): Is the athlete’s explosive strength index relative to their body weight. RC = Fmax / Tmax . W Or RFDmax / W

Reactive Strength Index (RSI): The athlete’s ability to produce a maximal concentric contraction in the shortest period of time that is preceded by an eccentric contraction. RSI = Fmax – Fmin / Contact Time

Strength Deficit: The difference in force production between movements incorporating the stretch shortening cycle and movements predominantly utilizing the concentric contraction.

When training for explosive strength we need to consider all the above components of explosive strength, i.e. taking into account the athletes specific neuromuscular structure that is required to produce maximal force as quickly as possible. However, if one of the “links in the chain” is missed, then the expression of Fmax will not be entirely possible. Therefore, when programming with an end goal of explosive strength in mind, we have to consider the full spectrum of strength and power training to ensure that our athletes reap the rewards of true training transfer.

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What are some of the methods used to evaluate explosive strength?

Although it is beyond the scope of this post to discuss all the possible methods of testing explosive strength in detail, I will aim to briefly address some of the most utilized methods in mainstream strength and conditioning.

One of the easiest methods of testing your athlete’s strength deficit is by calculating the difference between a countermovement jump height and squat jump height. This will allow the strength and conditioning professionals to identify the areas that their athletes need to work on. For example, a large deficit may indicate that more hypertrophy or strength development is required, whereas a smaller deficit may indicate that more stretch shortening cycle type work is required (See figure 3).

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The use of more expensive equipment such a the GymAware, Fitrodyne, force plates or contact mats allow for many different explosive strength test to be conducted. For example, strength and conditioning coaches are able to create force velocity and power curves with various lifts, such as squats, squat jumps, clean variations, bench press etc, to establish the neuromuscular development of their athletes.

Reactive Strength Index testing is another good measure that can be conducted using a force plate or contact mat. Depth vertical jumps from various heights (e.g. 30cm, 45cm & 60cm) will give you an overview of the reactive strength and neural firing rates of your athletes. This is important because a decrease in neural firing rates will cause a decrease a particular joint stability. The longer it takes for the muscles to contract in a dynamic environment the more susceptible your athlete is to ligamentous injuries.

Rate-of-force development and starting strength can be measured on a force plate with various movements such ad isometric mid-thigh pulls, counter-movement-jumps and squat jumps, just to name a few.

Lastly, some more common test that are used to identify athlete explosive strength with equipment that is more accessible are tests such as; medicine ball chest throws, medicine ball overhead throws, broad jumps as well as vertical jumps.

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