Friday, October 5, 2018

Liverpool vs Manchester City: Who are ready for selection?

The Liverpool vs Manchester City match will definitely attract most of the interest this weekend. Both teams have competed for the UEFA Champions League mid-week and this makes things slightly complicated. Are all players ready for selection? I tried to replicate a hypothetical scenario having player A and B and assuming they are both equally important for tactical reasons. I have applied simple sports science tools and is not my intention to interfere with coach role. The coach has the final word! This is just an example of how sports science could help in decision-making.
No doubt to implement a system like this you need first to build human relationships. To read more on that visit https://www.tandfonline.com/…/full/10…/24733938.2017.1377845  and https://hiitscience.com/coach-lets-do-hiit-today-hmm-not-a…/

Wednesday, September 26, 2018

“Coach, let’s do HIIT today!” “Hmm, not a good idea”.


How many times have you heard this? Let’s do HIIT to make us feel better? It’s not uncommon. High-Intensity Interval Training (HIIT) is popular, but in fact its popularity resides mostly amongst the scientists. Coaches are more conservative, and fear implementation of HIIT, at least as it is described in scientific papers. Indeed, the very first studies of the revised HIIT model from Canada described a HIIT protocol with repeated 30-sec all-out bouts on the bike while pedaling against an external load of 0.075 kp per kg body weight (Burgomaster et al., 2005). As the area evolved, more real-world protocols were developed (Iaia et al., 2008). Here, participants performed 8-12 x 30 sec bouts at 90-95% of their maximal running speed, with 3-min rest between. Billat et al. (2001a & b) proposed another programme that consists of repeated 15 sec high intensity bouts with 15 sec of low intensity or rest in between. I believe we are now in a position to say that we have some realistic proposals to put on the table for consideration by coaches. Martin and Paul have further advanced our knowledge, proposing easy to use protocols and ideas (Buchheit & Laursen, 2013a & b), which will be extended further in the book and course across 20 sport application chapters provided by practitioners embedded at the coalface of elite sport.

We now have the program. Our next step is to read behind the lines before we talk to the coach. With that being said, I’d like to put forth some hidden issues that are like to arise when you defend your plan to the coach.

Injuries
“Aren’t we at higher risk of injury doing HIIT compared to conventional football training”? The answer is both yes and no. We are at higher risk when we do HIIT if we haven’t respected the basic rule of progressive overload, which is fundamental to safe exercise training periodization. We recently showed this in a study, where conventional football training was complemented with adjacent HIIT sessions (Paul et al., 2018). Across 4 weeks, endurance performance was improved and no injuries occurred. It’s important to appreciate that injuries can be the consequence of lower than optimal fitness due to inadequate training. Indeed, the model proposed by Tim Gabbett suggests that low fitness itself may be a risk factor for non-contact injuries. In contrast, high levels of fitness may protect against injuries (Gabbett, 2016). Thus, a focus towards ensuring high aerobic fitness in our players should actually protect them from non-contact injury occurrence. Of course, this only occurs when we build the training program in a progressive manner.

Our limited resource – Time  
It’s important to appreciate that coaches have program to run. They are concerned more about training as a team, not as individual player. They have to be. That’s why today, most of our training time in football uses small-sided games (SSG), which are useful for building and maintaining match-specific technical and tactical elements (Lacome et al., 2018). Additionally, we know that playing SSG will assist to develop some of the match specific physical fitness elements at the same time. With full respect to use of this approach, SSG have limitations too. For example, SSG might not be specific enough to a player’s individual needs. Often, SSG won’t provide enough stimulus to build key football-specific elements like the ability to perform long intensive efforts.

The solution? 
Supplement your SSG with specific short interval HIIT. For example, you might use 2-3 sets of repeated 15-sec or 30-sec bouts at 90-95% of maximal speed (Billat et al., 2001a & b; Iaia et al., 2008). Another option would be to perform repeated bouts of either 30 sec at 110% of 30-15 intermittent field test (IFT) or 15 sec at 120% of IFT (Paul et al., 2018). All programmes do not require much time and bring great benefit.

After convincing yourself, the next step is to convince the coach. That’s either the easy or the hard part of the day, depending on your relationship. I’m talking about the human relationship, because that’s the foundation of any professional relationship. Building trust is key. I can’t emphasize the importance of this enough, or give you advice on how to go about this. Its personal. Ultimately, the ability to build trust in human relationships incorporates everything; who you are, where you come from, what your life expectations are, your values and beliefs – ultimately seeing the other person for who they are and they, in turn, seeing you. Are you there on the team to satisfy your personal inner needs and professional ambitions, or are you there to contribute to making the common team dream a reality? Do you believe science is everything or do you feel we are part of the team, a member of the family, where using science can help to make it better?

Of course there are theories from the social sciences, like the diffusion of innovation theory, which can help you further build your skills in effective communication of science. For those interested please read a recent editorial on this topic (Nassis, 2017). I’m not sure if it is so much knowing the science behind or trusting your intuition. After so many years, I tend to believe sometimes it’s good to trust your intuition, provided you have enough experience to trust in it, it will lead you in the right direction.

Going back to where we started. Maybe instead of “Coach, let’s do HIIT today”! How about we try another approach with a subtle change in wording:

“Coach, what do you think about doing HIIT today? Do you like the plan? Any ideas on how we could make it better?”

This post was first published at HiitScience on September 22, 2018

References




Burgomaster KA, Hughes SC, Heigenhauser GJF, Bradwell SN, Gibala MJ. Six sessions of sprint interval training increasesmuscle oxidative potential and cycle endurance capacity in humans.  J Appl Physiol 2005;98:1985-1990. 



Lacome M, Simpson BM, Cholley Y, Lambert P, Buchheit M. Small-SidedGames in Elite Soccer: Does One Size Fit All? Int J Sports Physiol Perform 2018;13:568-576.

Nassis GP. Leadership in science and medicine: can you see the gap? Science and Medicine in Football 2017;3:195-196.  

Paul DJ, Marques JB, Nassis GP. The effect of a concentrated period of soccer specific fitnesstraining with small-sided games on physical fitness in youth players. J Sports Med Phys Fitness 2018 Jun 27 [Epub ahead of print] 


Tuesday, September 25, 2018

Decelerations, accelerations, total workload and return to play: food for thought

Today, I had the chance to read a fantastic recent editorial on the nature of decelerations in football and their contribution on player's mechanical load. Here is the link to the full paper which I hope you enjoy.
With this opportunity, I had also the time to think more about the topic. No doubt that decelerations as well as accelerations should be taken into account when quantifying player's workload. With full respect to the great work published and despite the advances in knowledge regarding isolated risk factors for injuries, one of the key questions remains unanswered: what constitutes workload in football and team-sport athletes? Which indices should we trust in order to build effective injury risk estimation models? A couple of years ago we published an editorial with the hope to stimulate further discussions on the topic. I believe this paper is still relevant and hope you enjoy this read too https://bjsm.bmj.com/content/51/6/486

Monday, May 14, 2018

Real world research worth exploring: Machine learning algorithms in injury prevention



Today, I would like to comment on a recent paper reporting the use of machine learning algorithms to estimate injury risk in team sports athletes (López-Valenciano et al., 2018). Machine learning (ML) is a relatively new approach in sports medicine and science that applies certain algorithms, mostly without pre-defined assumptions, to solve complex problems like the sports injury prediction. As the name indicates, machine learning attempts to make computers "learn" and produce more and more accurate algorithms. As a discipline it integrates statistics with computer science.

In the study of López-Valenciano, a total of 132 male professional soccer and handball players underwent pre-season screening evaluation which included personal, psychological and neuromuscular measures. In addition, injury surveillance was employed to all musculoskeletal injuries during the season. The authors employed different learning techniques to check their accuracy in injury prediction.

Their results showed that the machine learning algorithms presented moderate accuracy for identifying players at risk of injury. From other studies, we know that ML accuracy can be improved with more data entered in the analysis. Nevertheless, the novelty of the study of López-Valenciano and colleagues is they showed that machine learning can assist in solving problems like the identification of players at risk. However, one should bear in mind that ML algorithms work well for the population they were created and we cannot predict what will happen with another set of data.

Tuesday, May 8, 2018

Real world research worth exploring: Accelerometer-based prediction of sports injury

analog.com


The use of accelerometers in studying the non-contact injury risk is a hot topic both in team and individual sports. Recently a research team from the University of California tested the hypothesis that the running-related injuries were the result of a combination of high load magnitude and strides number that result in accumulated microtrauma (Kiernan et al., 2018). During the studying period of 60 days, elite runners wore a hip-mounted activity monitor to record accelerations while training. From these accelerations the researchers estimated the vertical ground reaction forces (vGRFs). Their results showed that  the injured athletes had significantly greater peak vGRFs and weighted cumulative loading per run. 

The beauty of this study is the use of a common accelerometer to derive data associated with injury risk. Of course, these findings should be verified in bigger samples but the main message of this study is that this type of microtechnology, much cheaper that the GPS-embedded accelerometry, may assist in injury risk management for athletes/teams with limited resources.

Wednesday, May 2, 2018

Player performance metrics: time to reconsider our approach!



There are different performance metrics but most of them are looking at football performance in a fragmented way. For instance, match running distance at different speeds is considered as an important index, sometimes without taking into consideration the match context (player's position, opposition performance etc). 

Also, it seems that some actions, very decisive for the team performance, are not properly evaluated. As an example, in one moment in last night's match Bayern Munich striker defended very effectively against Ronaldo (at 6th minute of the match, match highlights here ). 

How would you rate an attacker's performance doing fantastic work while team is defending? Is it time to reconsider our approach and integrate physical performance  with technical and tactical data? Your thoughts?

Monday, February 5, 2018

How to test your players? 如何测试你的运动员的健身?

Fitness testing in football (soccer) can be a useful tool to 1) identify individual's needs, 2) reduce the risk of injuries, and 3) optimize training plans and performance. There is a number of tests that a sport scientist and practitioner can use. Before you choose, it would help if you answer the following questions:

-Why am I testing the players?
-What is my plan for the next month and the whole season?
-Which of the tests in the literature are valid, reliable and sensitive to training?
-Which of those that fulfill criterion 3 above, does my coach like?

To make it simple for you, I have summarized in table 1 below the most common tests. Their validity and reliability varies a lot and should you want to know the in-depth details you can read table 2 as well as our review paper on that topic (Paul & Nassis, 2015a). In general, all the below tests have acceptable validity and reliability.

While this is a guide, I advise you, especially the junior practitioners, before you go ahead and speak to the coach, better to have plan B too. Sometimes coaches may prefer a different test to the ones on the list. 


Table 1. Common tests used for fitness assessment in football (soccer)
Football Fitness Element
How to test?
Where can I find more info to back up my proposal?
 Sprinting ability
10-m, 20-m, 30-m, 40-m sprint
Paul & Nassis (2015a)
 Change of direction ability
T test
Slalom sprint
Slalom dribble sprint
Paul et al (2016) 
Huijgen et al (2010)
Huijgen et al (2010)
 Muscle strength/Power
Different types of jumps
Isokinetic dynamometry
Paul & Nassis (2015b)
 Aerobic fitness
 Yo-Yo intermittent recovery test
30-15 intermittent test
Bangsbo et al (2008)

Buchheit (2008)
Repeated Sprint Ability
7 X 30m or 6 X 20m 

Dribbling ability
 30-m slalom dribbling 
Huijgen et al (2010)



Table 2. Summary of the tests advantages and disadvantages (modified Paul & Nassis, 2015a)





Sources & related links

Bangsbo et al (2008). Sports Medicine 38(1): 37-51, read here

Buchheit (2008). Journal of Strength & Conditioning Research 22(2): 365-374, read here

Huijgen et al. (2010). Journal of Sports Science 28(7): 689-698, read. here

Paul, Gabbett & Nassis (2016). Sports Medicine 46(3): 421-442, read   here

Paul & Nassis (2015a). Pediatric Exercise Science 27(3): 301-313, read here

Paul & Nassis (2105b).  Journal of Strength & Conditioning Research 29(6): 1748-58, read here


Thursday, January 11, 2018

Coach, better to do whole body cryotherapy or cold water immersion?


This is a frequently asked questions by players and competitive athletes after they have completed prolonged and exhaustive exercise. Should you have the resources available in your club, this is a true dilemma. Both forms of cryotherapy, either whole body cryotherapy (BC) or cold water immersion (CWI) are used to speed up recovery. The suggested mechanism of potential beneficial effect of cryotherapy is associated with reduced inflammation, muscle damage and muscle soreness perception. Whether or not cryotherapy assists in a faster recovery of the functional capacity and sports performance is still debatable.

Whole body cryotherapy is gaining more popularity and this is due to the fact with this form of cryotherapy athletes can be exposed to far higher temperatures compared to CWI (around -85  °C vs. -10  °C). This level of air temperature during the whole BC is assumed to limit inflammation by reducing peripheral blood flow and, hence, speed up recovery after exhaustive exercise. However, there is very little evidence to support this assumption. Therefore, the effect of whole BC vs CWI is still under investigation.

In a recent study, published in the European Journal of Applied Physiology, 31 trained but recreational runners completed a test marathon and following the run they were allocated in 3 groups in terms of the recovery means they used: the CWI group, that immersed lower limbs and iliac crest at water of 8 °C for 10 min; the whole BC group, that was exposed to two cold treatments in a cryotherapy chamber (3 min at − 85 °C  followed by a 15-min warming period in ambient temperature + 4-min bout at − 85  °C); and the placebo group. Participants in the placebo group consumed 2 × 30 ml per day of a fruit flavored drink which did not contain any antioxidants or phytonutrients 5 days before the run, in the day of the run and for 2 days after. In this group, participants were simply asked to rest in ambient temperature for 10 min following completion of the marathon.

The results of this study showed that the implementation of a cryotherapy intervention resulted in at least unclear effects for every outcome measure when compared to the placebo intervention. As the authors state in their manuscript it seems that any beneficial effect of cryotheraphy after exercise is simply a product of the placebo effect.

These findings support the idea of planning the recovery strategy that best fits the beliefs and the needs of the individual athlete.


Source

Wilson et al (2018). Recovery following a marathon: a comparison of cold water immersion, whole body cryotherapy and a placebo control. European Journal of Applied Physiology 118:153-163.

Tuesday, January 2, 2018

The best scientists get out and talk to the coaches

Are you a sport scientist and medical team member wondering why the coaches can't understand you? To make you feel better let me say you are not the only one. In a survey with high level football club staff it was reported that their injury prevention programs' effectiveness was lower than initially expected. The reason being the low coaches' engagement (1).

As many would agree there is a gap between the staff in the lab and the treatment room and the coaches. Sometimes or most of the times they don't speak the same language. What can we do? Let's start with small changes. The first step is to get out of the lab and talk to the coaches. Talk to them using a language they can understand. Talk when it's needed and communicate what's important. Day by day communication will build trust. Trust will build confidence in your relationship and, with time, trust and confidence will make things better.

The figure below is a short description of steps that could help in making the connection between team members stronger. Should you want to read more on tips of more effective communication you can read this article


Figure 1. Four tips to become a better professional.





For further reading
1.Akenhead and Nassis (2016). Training load and player monitoring in high-level football. Int J Sports Physiol Perform 11(5): 587-593  here

Thursday, July 27, 2017

Why RPE is not the best tool to identify athletes in risk of injury?

Published 
J Strength Cond Res. 2017 Aug;31(8):e77-e78. doi: 10.1519/01.JSC.0000522116.12028.06

Reply to Manuscript Clarification for the paper:
Brito J, Hertzog M, Nassis GP. Do match-related contextual variables influence training load in highly trained soccer players? J Strength Cond Res 30:393-399, 2016.

Title:
Workload assessment in soccer: an open-minded, critical thinking approach is needed

George P. Nassis1, Maxime Hertzog1 and Joao Brito2


We acknowledge the journal for giving us the opportunity to highlight the key findings and clarify any misunderstandings to the authors (1). Our practical advice that “coaches need to take into consideration that training loads are affected by match-related parameters“ is based on actual data which showed that 1) higher weekly loads were reported after a defeat or draw compared to a win, and 2) when preparing to play against a medium level team, average sRPE during the week was higher than that before playing against a top or bottom team (2). With reference to the first point, we commented in the paper that “it was not possible to conclude whether this was a consistent coaching strategy or whether it denoted the difficulty the coaches have to create training sessions as demanding as official matches”.
Our findings are in line with the literature showing that the complex interaction of many factors that contribute to the personal perception of physical exertion, including hormonal and neurotransmitters concentration, substrate levels, external factors (environment, spectators), psychological states, previous experience and memory may limit the use of RPE in accurately quantifying training intensity and workload (3, 4). This might explain the high variability we found in sRPE (5–72%). Objective methods, like heart rate monitoring, are suggested as a more accurate way of internal workload calculation. The limitations of RPE use in soccer have also been presented elsewhere, with the correlation coefficients between sRPE and heart rate-based training load ranging from 0.50–0.61 (5).
Regarding the second point of this letter stating that the training content of our study was not controlled, we believe this point has been made clear in our manuscript. In fact, this is one of the limitations of sRPE; the fact that no account is taken for the external load. As mentioned on the letter, the authors “are aware that such a study design is almost impossible to set at elite soccer level” (1). Therefore, there is no disagreement between the letter’s authors and us.
In summary, our study showed that a RPE-based workload calculation is not without limitations and this should be taken into account from scientists and practitioners. Indeed, this point has been raised by others as well (3, 4). Studies showing low-to-moderate correlation coefficients between RPE and GPS-derived workload data are on the same line (6). As mentioned by the letter’s author previously, “despite various contributing factors, session rating of perceived exertion has the potential to affect a large proportion of the global sporting and clinical communities” (7). We believe our study has indeed highlighted some of these “contributing factors”. As we acknowledge in our manuscript, “the sRPE is a practical low-cost tool to assess training load in soccer”. However, this does not justify that it can be an accurate and sensitive method in all cases, and all its limitations should be considered. Either subjective or objective data should be combined, or one should move towards assessing the training physiological outcome and eliminate the use of subjective tools, especially with elite players (8, 9). There is a risk of spreading inappropriate information by presenting RPE-based method as the gold standard for workload quantification. We strongly suggest a more open-minded and critical thinking approach to the related data presented in the literature. This approach might help advance the knowledge in the field which at the moment is superficial and of limited extent.


References:
1.    Chamari K, Tabben M. Manuscript clarification. J Strength Cond Res, 2017.
2.    Brito J, Hertzog M, Nassis GP. Do match-related contextual variables influence training load in highly trained soccer players? J Strength Cond Res 30: 393-399, 2016.
3.    Borresen J, Lambert MI. The quantification of training load, the training response and the effect on performance. Sports Med 39:779-795, 2009.
4.    Abbiss CR, Peiffer JJ, Meeusen R, Skorski S. Role of ratings of perceived exertion during self-paced exercise: what are we actually measuring? Sports Med 45:1235-2143, 2015.
5.    Impellizzeri FM, Rampinini E, Coutts AJ, Sassi A, Marcora SM. Use of RPE-based training load in soccer. Med Sci Sports Exerc 36: 1042-1047, 2004.
6.    Weston M, Siegler J, Bahnert A, McBrien J, Lovell R. The application of differential ratings of perceived exertion to Australian Football League matches. J Sci Med Sport 18:704-708, 2015.
7.    Haddad M, Padulo J, Chamari K. The usefulness of session rating of perceived exertion for monitoring training load despite several influences on perceived exertion. Int J Sports Physiol Perform  9: 882-883, 2014.
8.    Akenhead R, Nassis GP. Training load and player monitoring in high-level football: current practice and perceptions. Int J Sports Physiol Perform 11: 587-593, 2016.
9.    Nassis GP, Gabbett TJ. Is workload associated with injuries and performance in elite football? A call for action. Br J Sports Med 51:486-487, 2017.




Monday, May 1, 2017

The Transition Period in Soccer: A Window of Opportunity

Below is a review paper we published last year with relevant points and practical advises. Should you are interested in learning more please click on the link here and send me an email. Limited copies will be provided. The infographic is by Dr Yann Le Meur.



 2016 Mar;46(3):305-13. doi: 10.1007/s40279-015-0419-3.
The Transition Period in Soccer: A Window of Opportunity.
Silva JRBrito JAkenhead RNassis GP
Abstract
The aim of this paper is to describe the physiological changes that occur during the transition period in soccer players. A secondary aim is to address the issue of utilizing the transition period to lay the foundation for the succeeding season. We reviewed published peer-reviewed studies if they met the following three selection criteria: (1) the studied population comprised adult soccer players (aged >18 years), (2) time points of physiological and performance assessments were provided, and (3) appropriate statistics for the calculation of effect sizes were reported. Following two selection phases, 12 scientific publications were considered, involving a total sample of 252 players. The transition period elicits small to moderate negative changes in body composition, a moderate decline in sprint performance with and without changes of direction, and small to moderate decrements in muscle power. Detraining effects are also evident for endurance-related physiological and performance outcomes: large decrements in maximal oxygen consumption V̇O2max) and time to exhaustion, and moderate to very large impairments have been observed in intermittent-running performance. Off-season programs should be characterized by clear training objectives, a low frequency of training sessions, and simple training tools in order to facilitate compliance. The program suggested here may constitute the 'minimum effective dose' to maintain or at least attenuate the decay of endurance- and neuromuscular-related performance parameters, as well as restore an adequate strength profile (reduce muscle strength imbalances). This periodization strategy may improve the ability of players to cope with the elevated training demands of pre-season training and therefore reduce the risk of injury. Moreover, this strategy will favor a more efficient development of other relevant facets of performance during the pre-competition phase (e.g., tactical organization). We contend that the transition period needs to be perceived as a 'window of opportunity' for players to both recover and 'rebuild' for the following season.

Friday, April 21, 2017

Injury prevention training in football: Time to consider training under fatigue?

dailystar.co.uk

 by Darren Paul, Joao Brito, George Nassis
published in Aspetar Sports Medicine Journal (download pdf here)

Muscle injuries often occur towards the end of each half and this has been associated with fatigue (1). Current practice often means injury prevention training is performed at the start of the session. The hypothesis is that when training is performed in a fresh state it allows players to demonstrate better form. In this article we will look at fatigue, fitness and training order to question this existing practice and build a case for performing injury prevention at the end of practice, when in a fatigued state.

DEMANDS OF FOOTBALL
Football is a sport where players perform bouts of high intensity activity interspersed with periods of lower intensity. The demands are increased by having to execute complex movements such as accelerating and decelerating, changing direction, jumping and tackling, parts of which are likely to impact on the characteristics of the match (2). To do this players need an appropriate level of fitness, namely moderate-to-high aerobic and anaerobic power, good agility, flexibility and muscular development and the ability to generate power during fast movements. Although players may not excel across all of the physical components, they should possess levels that will allow them to remain competitive for the whole match.

It is clear that physical qualities are not the only determinant of match performance. The outcome of a match depends on the complex interaction of several physical, psychological, technical and tactical factors. The work rate of a player in a match is also dependent on many other factors. Some of these are:
  • the quality of the opposition,
  • changes in positional role,
  • the effects of previous and/or forthcoming game commitments,
  • environmental conditions,
  • dehydration,
  • cultural differences and other intrinsic and extrinsic factors.

One example of the complexities is the distance covered. In the English Premier League players from less successful teams cover significantly greater distances in high-intensity activities than their more successful counterparts(3). The opposite was found in Italy where players of the most successful teams from the Italian Serie A perform more high-intensity activities during a game when in possession of the ball compared with players of less successful teams(4). It is improper to suggest that superior fitness and/or players'/teams' levels will manifest in higher amounts of effort during any given match.

FATIGUE
Given the demanding nature of football, players will likely experience a degree of transient or accumulated fatigue at some stage of the match. The oversimplification of interpreting this with time-motion analysis is that players tend to experience this fatigue or/and impaired performance mainly after short-term, intense periods in both halves and towards the end of the match(5). However, basing assumptions regarding physical fitness and fatigue purely on activity profile statistics is flawed; particularly given that our understanding of physiological responses during match activity remains limited. For example, it is still unknown to what extent the dynamic responses to match demands (such as accumulation of metabolites in muscles, plasma osmolality, substrate availability, body temperature and dehydration) prevent total breakdown of any single peripheral physiological system, either prematurely or in the final periods of the match(6).

Fatigue has become a hot topic in football despite being regarded as a complex and multi-factorial entity. There is growing interest as to how fatigue relates to recovery, player fitness and effort during matches. To avoid exhausting themselves before the final whistle, players are likely to adopt a pacing strategy that allows them to be involved in demanding and critical moments, even during the final stages of a match. The regulation of self-chosen high intensity activity is also an important product of training, as players need to learn to adopt pacing strategies that will allow a high effort even during the final stages, or when required. For example, an early sending off might increase the overall work rate of outfield players. Hence, there is likely a demand to cover more distance in order to counteract the numerical disadvantage. This may result in higher levels of fatigue towards the end of the game(6). The large match-to-match variability of individual player work rates, particularly high intensity activity, as a representation of time-motion analysis means players are unlikely to perform to their maximal capacity during most matches.



FITNESS
When planning training sessions, coaches should take into account that playing and training affect each individual player differently. One of the objectives of a fitness test battery is to identify differences in players' physical characteristics. A variety of fitness tests are currently used to monitor performance and evaluate training response. Unfortunately, there is no exact measure for ‘physical performance’ in a football match. This stresses the fact that individual performance in fitness tests should not be used to directly predict performance in competition. Nonetheless, player fitness should be considered as a factor that contributes to match result. This means that using fitness tests together with physiological data might be useful for monitoring performance measure changes and directing training prescription. If testing and/or monitoring are not done often, coaches might not detect adaptations, which can occur faster than the time between tests. From an applied perspective, this remains a challenge, as coaches are sometimes reluctant to sanction frequent testing within the season. This is despite the fact that routine monitoring may aid periodisation strategies, prevent under/overtraining and maintain players in optimal condition.

A relevant question when planning training sessions relates to fatigue. This is important as muscle injuries (e.g. hamstring strains, the most prevalent muscle injuries in football) typically occur in the latter stages of a match(7). Interestingly, fatigue during the match has been associated with decreased eccentric strength and flexibility(7). Most joint sprains also occur towards the final stages of each half of the match. We think that this might be associated with fatigue-related changes in neuromuscular control, joint dynamic stability, and postural control. This may result in players performing ‘different’ movement patterns than when they are fresh. Fatigue may lead to players using potentially injurious landing and turning techniques that occur during the later stages of football activity. Evidence to support this theory was seen using a 90-minute intermittent exercise protocol, representative of football match play. During the protocol, players had time-dependent impairments in sprinting kinematics, peak eccentric hamstring torque, functional strength ratio and overall sprint performance during the latter stages of the test(7). Such research supports our hypothesis that fatigue is a major injury risk factor of match play.

Low fitness level is thought to be an injury risk factor for players(3). Therefore, practitioners often try to elevate physical fitness in the belief that this will reduce the incidence of fatigue and accompanying injury. It cannot be overlooked, however, that players with greater physical fitness will simply work at a greater, rather than reduced, relative intensity, the implication being players may still suffer from fatigue. Players tend to perform less physical work and fewer skilled actions in the second half of a match compared to the first, regardless of ability. However, given that players may rarely perform to the maximum capacity in a match, the relationship between maximal (test) performance, fitness and injury occurrence is far from simple. This is likely to have profound implications for conditioning as part of the training programme. Despite such knowledge, there appear to be few time-related guidelines on when to embed injury prevention training into the practice sessions.

Resistance to fatigue is a key factor for a player to continually perform throughout the whole match. Indeed, the player’s performance in response to training can be estimated from the balance between a negative (fatigue) and positive function (fitness). There is a fine line between improving fitness and negatively overloading the player, which could cause injury. There is now growing emphasis placed on monitoring training loads (using global positioning systems, heart rate monitors, time-motion analysis and subjective scales such as rate of perceived exertion) to allow teams to better manage and monitor training loads. Such tools are commonly used within the applied setting and are deemed important to develop performance-enhancing training guidelines.

TRAINING ORDER
The issue of training order is considered an important factor in the design of training programmes. Generally, this con-cept has been considered with regards to the order of endurance and strength training and a possible interference effect(8). Either order of training has its advantages and disadvantages. This means it is important to consider the objective of the training session. For example, residual fatigue from the endurance component of concurrent training may compromise the ability to develop tension during the strength element of concurrent training. Essentially, there appears a likely trade-off that needs to be considered in view of the training goal.

SPECIFICITY
The law of training specificity states that the specific nature of a training load produces its own specific response and adaptations(9). By inference, it would seem training in a fatigued state may improve performance in a fatigued state, too. In terms of injury prevention training, it seems the general approach is to perform drills earlier at the start of the session, often in a non-fatigued state. The justification is that players perform efforts in a ‘fresh condition’ that allows the musculature to produce the appropriate responses of protective function in maintaining stability, balance and body control. We propose some injury prevention training would be effective when performed after rather than before fatigue sets in. The reality of the match means that players will execute specific tasks in both non-fatigued and fatigued conditions. Hence, it would seem training in both conditions might benefit the players.

Research has started to examine the effect of injury prevention training under fatigued conditions. The limited number of studies available have mainly been conducted in semi-professional football players and more studies in professional players are needed. In one study, eccentric strength training conducted post-training was shown to significantly reduce the negative influence of fatigue on hamstring strength(9). Following the 8-week intervention, players who performed the training fatigued, compared to non-fatigued, showed better maintenance of eccentric hamstring strength and preserved functional eccentric hamstring to concentric quadriceps stre-ngth ratio during an intermittent test. A real life significant reduction in match-play hamstring injury rate in Australian Rules football was shown following an intervention strategy, including a football-specific eccentric hamstring strength drill, performed in a fatigued state(10). The protective qualities may apply to other intrinsic factors that can be trained. For instance, a greater improvement in balance ability was observed when balance training was performed after, rather than before, football training(11). This means that training in a fatigued state could also be applied to proprioception. Intuitively, the application of this as a training strategy is largely dependent on the trainers’ objective within the session. However, we recommend that the timing for injury prevention training, including eccentric strength training, core stability, neuromuscular control and balance drills, should vary between training sessions as a strategy to improve adaptability to the specific demands of the game.



CONCLUSION
In conclusion, we recommend practitioners consider performing injury prevention training in a fatigued state too. By exposing the player to training under fatigue, we can better prepare them for the demands of the match. This strategy might assist in reducing the match fatigue-related injuries.
 Published in Aspetar Sp Med Journal


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