MUSCLE INJURY PREVENTION IN ELITE FOOTBALL PLAYERS, WHAT EXERCISES WORK?
Muscle injuries are a major concern in the world of football. Therefore, the focus on preventive strategies for muscular injuries is fundamental.
GSSI FCB Sports Nutrition Conference: Recovery Nutrition for Football
Rollo, I* and van Loon, L.J.C
Nutrition in football has historically been low of the list of priorities as coaches and team physicians prepare players for competition. The term “building a team” typically refers to the recruitment of new players, staff and the experimentation with tactics in pursuit of winning performances. However, in literal terms it is the nutritionist/sports dietician who may in fact have the biggest impact on “building” a successful team.
The development of techniques to intrinsically label protein have provided evidence that ingested foods are used to build new tissues in the human body (van Loon et al., 2009; Pennings et al., 2011). Therefore, the body of a footballer is a product of the foods and nutrients ingested daily. Furthermore, stable isotope methods have allowed the protein synthesis rates of various body tissues to be direct quantified and rates of turnover calculated (Koopman et al., 2006). Subsequently, we know that the footballers’ body is in a constant state of flux and that vital tissues such as skeletal muscle are continually being degraded and resynthesized.
In professional football, the physical demands of matches have become more intense (Bush et al., 2015). In addition, the congested fixture schedule coupled with the reduced recovery duration between matches contributes to an increased risk of injury (Dellal et al., 2013) and reduced physical performance (Rollo et al., 2014). The aim to todays conference is to combine theory and practice of recovery nutrition. Specifically, the “science” of sports nutrition provides the evidence and rationale to inform the “practical” nutrition recovery strategies. Here we introduce the two sessions of the conference , protein and hydration and discuss the relevance of nutrition in “building a team”.
The conference will begin by addressing the topic of protein. The proteins in a players body are constantly broken down into amino acids and these amino acids then become available for the synthesis of other proteins. New amino acids are delivered through nutrition, whilst excess amino acids are either oxidised or metabolised to fatty acids or glucose. Muscle is an important tissue being responsible for 25-30% of whole body protein metabolism. The quantity of skeletal muscle will depend on the size and body composition of the player. The contractile fibres within muscles and enzymes needed for biochemical reactions in the players body are all examples of proteins. An average 70 kg male player contains approximately 12 kg of protein and 220 g of free amino acids.
Many of the adaptations we are interested in to promote performance in football occur within the muscle. The balance of protein synthesis and degradation dictates whether net protein synthesis occurs. If protein degradation rates are greater than the rates of synthesis, there will be a reduction in protein content; conversely, muscle protein content can only increase if the rate of synthesis exceeds that of degradation. Research has mostly focused on protein synthesis but both processes (breakdown and synthesis) are important. It is believed that protein synthesis is the main driver of positive protein balance because protein breakdown does not change as much. On the other hand, it is also believed that protein degradation is important to remove damaged proteins and allow new proteins to be synthesized. Thus, the key to rapid recovery is increasing protein turnover (synthesis as well as breakdown), not just reducing breakdown (Phillips & Van Loon 2011; Phillips 2014).
Skeletal muscle has a turn-over rate of approximately 1-2% per day. Therefore, the leg muscles for example used to, transport the player, pass the ball and score a goal, would theoretically be completely “new” in a 6-week period. Thus, over the competitive season a player’s entire muscular system may be broken down and rebuilt approximately six times. Guidelines for daily protein intake for a 70 kg player are in the range of 1.3-1.8 g/kg per day (Phillips & Van Loon 2011). This equates to about 120 g of protein divided over 6 meals, interspersed by about 3 h, with each meal containing approximately 20 g of protein (Phillips and Van Loon 2011). However, protein synthetic response after exercise may be accelerated by optimising the quantity (Moore 2015), timing (Tipton 2007; Tipton et al., 2007; Beelen et al., 2008) and quality (van Loon 2012) of protein intake following training and matches.
The tendons and connective tissues such as ligaments are vital for football performance, as it is these tissues which hold the muscular skeletal system together and stabilise movement around joints. Strains and sprains of soft tissues (tendons and ligaments) account for more than 60% of all injuries reported in the English Premier League (Hawkins et al., 2001). The physiology of tendons and ligaments is different to muscle (Kjaer et al., 2009). This is because tendons and ligaments have limited blood flow, and they are dependent on nutrient delivery though bulk fluid flow (Baar 2015). The turn-over of tendon is significantly lower than muscle.
Nevertheless, early evidence suggests there are opportunities for remodelling of tendon tissue which can be augmented by nutrition. This is because ingested protein may add to the successive rings of collagen that surround the core making the structure stronger. Specifically, the ingestion of gelatin has been reported to be effective in increasing circulating concentrations of the amino acids glycine, proline, hydroxyproline, and hydroxylysine (Shaw et al., 2016). Furthermore, the ingestion of gelatin (15 g ingested with 50 mg vitamin C) 1 h prior to exercise increased blood markers (amino-terminal propeptide of collagen I) related to increased collagen synthesis (Shaw et al., 2016). Although more research is required, the ingestion of gelatin is a promising nutritional intervention to improve both the function of connective tissues and speed the recovery from musculoskeletal injuries. Furthermore, this intervention may be of great relevance to those populations who experience a high incidence of ligament injury, such as female players (Celebrini et al., 2012; Celebrini et al., 2014; De Ste Croix et al., 2015).
Given the low turnover rate of tendons, players will likely have the same “core” tendon protein between the ages of 17 years and 70 years of age (Heinemeier et al., 2013). Therefore, players will have the same tendons throughout a season and their competitive career. However, as studies which have provided proline with vitamin C have reported improved collagen synthesis (Paxton et al., 2010), remodelling is possible throughout the season with appropriate loading and nutrition (Shaw et al., 2016).
In the afternoon, the third session of the conference focuses on hydration and fueling. The amount of water a player has in their body will depend upon their body size and body composition. Greater quantities of lean mass are associated with greater total body water. Thus, players body water content may range from approximately 30 L to 50 L, accounting for 55-70% of body mass respectively (Wang et al., 1999). The water content of the body in healthy players is well regulated (Raman et al., 2004). However, as players engage in football training and matches the rate of fluid turnover is significantly increased. This is because in both cool and hot environments, sweating provides the primary mechanism to dissipate the metabolic heat generated as a consequence of playing football (Ekblom 1986; Shirreffs et al., 2005). Sweat rates in footballers have been reported to range from 0.5 L·h-1 to 2.5 L·h-1 (Broad et al., 1996; Maughan et al., 2005; Shirreffs et al., 2005; Da Silva et al., 2012; Baker et al., 2016; Nuccio et al., 2017).
If we assume a higher level of total body water i.e. 50 L; in cool low intensity training environment total body would turn over in approximately 100 playing hours. However, during match play in warm environments, at a modest sweat rate of 1.5 L·h-1, total body water would turn over in approximately 33 playing hours. In practical terms, total body water would turn over in just under four weeks for a player completing 2-games a week and a 1 h training session between games. Thus, over a 38 week season a player’s total body water may turnover a conservative ten times.
Both acute and chronic hypohydration equivalent to deficit of >2-3% of pre-exercise body mass during exercise may increase cardiovascular strain (Armstrong et al., 1997), impair cognitive function (Ganio et al., 2011; Nuccio et al., 2017) and increase the perception of effort (McGregor et al., 1999). This may manifest as reduced physical (Mohr & Krustrup 2013) and technical (McGregor et al., 1999) football performance. To this end, after exercise players should aim to replace any fluid deficit (Maughan & Leiper 1995). Normal eating/drinking practices are, in general, sufficient to restore euhydration. However, during pre-season or periods of fixture congestion, rapid and complete rehydration can be achieved by drinking 1.5 L of a sodium-containing fluid for each 1 kg of a player’s body mass loss (Thomas et al., 2016). Strategies such as weighing players in and out of training allow individualised drinking plans to be developed and thus fluid turnover to be monitored (Maughan & Shirreffs 2008).
The brain is the vital, yet often forgotten about organ for football performance. Although player psychology is beyond the scope of this article, it is the brain which must convey space, make tactical decisions, regulate body processes and drive the recruitment of muscle to complete the physical movement required for football. Decision making and the ability to make the correct decision at high speed are likely key points of differentiation between elite players and their recreational counterparts.
There are clear reasons why there has been limited information regarding the brain tissue and rates of protein synthesis in vivo in humans. However, a recent study by Smeets and colleagues used stable isotope methods to directly assess brain protein synthesis rates in patients undergoing a temporal lobectomy (Smeets et al., 2018). Fascinatingly, brain tissue protein synthesis rates were 3-4-fold higher than skeletal muscle tissue, much higher than previously assumed. Accordingly, this hypothetically equates to the players brain being completely regenerated over a duration of 2 weeks. Therefore, players will, theoretically, have 20 “new” brains over a competitive season. This research is its infancy and the impact of diet and exercise, as well as the impact of football activity per se such as repeated heading of the ball, may have on brain protein turnover are yet to be established.
Based on the available literature firm nutritional guidelines to support brain protein remodelling cannot be made. Prudent advice would be to ensure the player maintains an adequate hydration status, especially if playing in the heat (see fluid section above) (Maughan et al., 2007) and protein intake (Phillips & Van Loon 2011). In addition various supplements may be considered, the main compounds presently under investigation and of interest are omega 3 fatty acids and creatine (Ashbaugh & McGrew 2016). This is because the ingestion of high dosages of omega 3 fatty acids may improve the short term outcomes following head injuries such as concussion (Lewis 2016). This may be achieved via neurite growth, increased neurite branching, and subsequent synaptogenesis, resulting in enhanced synaptic function and improved neuronal repair after a head injury (Kim & Spector 2013). Furthermore, the ingestion of omega 3 fatty acids has been reported to normalise levels of proteins associated with neuronal circuit function and locomotor control after sustaining a concussion (Wu et al., 2011). Supplementation with creatine monohydrate has been reported to improve cerebral energetics (Pan & Takahashi 2007; Turner et al., 2015). This may result in improved cognition, communication, self-care, personality, and behaviour (Sakellaris et al., 2006), all relevant to football performance and potentially brain remodelling (Sakellaris et al., 2008).
A footballer’s body is continuously rebuilding itself from the substrate provided via the diet. Thus, physically, the player that begins a season may be almost a completely different player by the end of the season. Observations from science highlight the important of appropriate practical nutrition strategies to optimize the remodeling of tissues to “recover” and “build” capable, resilient footballers.
*Disclaimer: Ian Rollo is an employee of the Gatorade Sports Science Institute, a division of PepsiCo, Inc. The views expressed in this article are those of the authors and do not necessarily reflect the position or policy of PepsiCo, Inc.
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