Football (Soccer) Needs Analysis
Football is a sport that is fuelled through both aerobic and anaerobic metabolism. A players dominant source of energy will be delivered through aerobic metabolism, however the most decisive football actions are likely to be anaerobic in nature (Wragg, Maxwell, & Doust 2000). The physical demand of football is usually high – with some research claiming that the average work intensity is close to anaerobic threshold; measured as a percentage of maximal heart rate (Stølen, Chamari, Castagna & Wisløff, 2005). This research suggests that an ideal player will have high aerobic capacity, as well as the ability to recovery quickly from anaerobic actions.
Time motion analysis, through the use of video or global positioning systems (GPS) has allowed scientists to quantify physiological data on individual players and playing positions (Al-Hazzaa, Alumuzaini, Al-Rafaee et al 2001). Football players cover approximately 10-12km of ground per game (Bangsbo & Michalsik 2002), however this approximation will fluctuate due to variance between playing positions. Midfield players are shown to run the furthest distances during a single match, and normative data shows that professional players run greater distances than amateurs (Mohr, Krustrup, & Bangsbo 2003). Football players are required to repeatedly produce high intensity, fatiguing efforts that can affect the outcome of the match (Bradley, Di Mascio, Peart, Olsen, & Sheldon, 2010). Some research has shown that exercise intensity during the second half of games is usually lower, and the sum of distance covered is less in comparison to the first half (Rienzi, Drust, Reilly, Carter & Martin (2000), although a study into elite football players in England showed contrasting results; Di Mascio and Bradley (2013) found that, on average, players completed their most intense bouts of exercise during the second half. This may suggest that elite players are more capable of maintaining anaerobic abilities than their moderate / amateur counterparts, as shown by Mohr, Krustrup, & Bangsbo (2003), who found that elite players sprinted 58% (P < 0.05) more than ‘moderate’ players.
It is estimated that players will be required to sprint for 2-4 seconds every 90 seconds in a game (Bangsbo, Nørregaard & Thorsoe 1991), with sprinting contributing to between 1 and 11% of a players total distance coverage in a match (Van Gool, Van Gerven, & Boutmans, 1988). Attackers (0.69km ± 0.08km) and lateral defenders (0.64km ± 0.06km) have been found to cover greater distances (P < 0.05) sprinting than midfielders (0.44km ± 0.04km) and central defenders (0.44km ± 0.03km) (Mohr, Krustrup, & Bangsbo 2003). Anaerobic activity demands account for approximately 3% of total game time in professional football, with this figure often doubling during the most intense periods of the game; indicating a high demand for anaerobic capacity (Di Mascio and Bradley 2013). These are important findings for the strength and conditioning coach to consider, as they highlight to the coach the importance of understanding repeated sprint capacities that player will benefit from having.
In addition to sprinting ability, footballers also need to have high endurance capabilities. Research estimates that players bodies will be subjected to; 15 tackles, 10 headers and 50 actions with the ball during a game, whilst also being involved in high intensity intervals every 70 seconds (Helgerud, Engen, Wisloff, & Hoff 2001; Mayhew, & Wenger, 1985), in total; players may be required to perform up to approximately 1400 ‘short’ actions in a game (Rienzi, Drust, Reilly, Carter, & Martin, 2000). Di Mascio and Bradley (2013) studied high intensity periods of elite football matches and found that, on average, the most intense periods of the game were immediately followed by periods that were 15% less intense than the match average. These findings support previous research by Mohr, Krustrup, & Bangsbo, (2003) who observed a considerable reduction in high intensity running following the 5 minute period where the most high intensity running was performed. This is also in agreement with Bradley and colleagues (2009) who reported that high intensity running was reduced (≥14.4-15 km / h -1) following high intensity bouts in both amateur and professional athletes.
In agreement with Withers et al – who found that lateral defenders sprinted 2.5 times further than central defenders - Di Mascio, & Bradley, (2013) also found that lateral defenders and wide midfielders showed the greatest levels of high intensity distance running as well as demonstrating the capacity to recover faster than players in other positions. Inclusion criteria for this study were strong, with 100 players randomly selected from English premier league clubs. Data collection and analysis was completed through time motion analysis of games in which teams in a similar league position competed and each match was at the same time of day. Environmental factors couldn’t be controlled and may have affected some of the data. The data showed that during the most intense periods of the game, work:rest ratios changed drastically from 1:12 (match average) to 1:2, with around 30 seconds of rest between high intensity actions. This finding highlights the importance of the strength and conditioning coach to manipulate training in order to prepare players to have the ability to recover quickly during high intensity periods.
Mohr, Krustrup, & Bangsbo (2003) studied players recovery capacities through research with highly elite players over a course of three seasons. Elite players performed far better in Yo-Yo intermittent recovery tests, running 10.7% further than their ‘moderate level’ counterparts. In addition to the previous research already mentioned, midfield and lateral players performed better in the test than both central defenders and attackers.
In order to establish a players energy expenditure in a game of football, research suggests finding the relationship between heart rate (HR) and oxygen uptake (VO2) (Hoff, Wisløff, Engen, Kemi., & Helgerud. 2002). Studies by both Bangsbo (1994) and Esposito et al (2004) support this idea, finding validity in the HR- VO2 relationship in intermittent exercise after drawing comparisons between HR and VO2 over various levels of exercise intensity. Astrand (2003) found that an exercise intensity of 85% maximal heart rate is equal to around 75% VO2 max. Studies show that the VO2 max of professional outfield male football players ranges from around 50-75mL/kg/min and goalkeepers – 50-55mL/kg/min (Stølen, Chamari, Castagna, & Wisløff, 2005), figures that are far higher than those documented in various studies from the 1980s (Ekblom, 1986; Faina, Gallozzi, Lupo, Colli, Sassi, & Marini, 1988). Anaerobic threshold is said to be between 76.6% (Casajus, 2001) and 90.3% (Vanfraechem, Tomas, 1993) although naturally, the majority of research has found anaerobic threshold percentage to be between these figures. Unfortunately, there are extremely wide variances in methodology as well as inclusion criteria and statistical analyses, which is why there is a wide range of reported anaerobic thresholds. Helgerud, Hoff, & Wisloff, (2002) studied gender differences in strength and endurance of professional football players, reporting that male and female players utilised anaerobic and aerobic energy systems similarly.
Research in to youth exercise physiology suggests that VO2 max should be proportional to body mass (mb) which is raised to the power of 0.67 (Åstrand, Rodahl, Dahl, Stromme, S.B. 2003), however there is some confusion as to how VO2 max should be expressed; with Nevill, Brown, Godfrey, Johnson, Romer, Stewart, et al, (2003) claiming that VO2 max should be raised to the power of 0.75-0.94 over a variety of bodyweights. Although incorporating a scaling procedure may be complex; it should certainly take place, as attempts to improve capacity without one are likely to result in skewed evaluations and inappropriate training programmes (Stølen, Chamari, Castagna, & Wisløff, 2005). Expressing VO2 in relation to mb with youth athletes requires an understanding of the effect that aerobic capacity has on aerobic performance. Although it’s known that on field performance is influenced by aerobic capacity (Helgerud, Engen, Wisloff, & Hoff. 2001); extraneous variables, such as tactics and opposition, are certainly likely to affect aerobic performance in some way. Therefore, it is appropriate and intuitive to enhance aerobic performance through the development of aerobic capacity, which should be achieved through the use of appropriate body mass scaling procedures (Svedenhag, 1995).
Kicking is a key action in football, knowledge of which is important to obtain when devising training programmes (Lees, Asai, Andersen, Nunome, & Sterzing, 2010). Kicking is a throw-like action, which requires distal segments of the body to ‘lag’ behind proximal ones as they move forwards (Dörge, Andersen, Sorensen, & Simonsen, 2002), kicking could also be described as a whipping action whereby a summation of forces lead to the high velocity action (Rodano, & Tavana, 1993). There are many extraneous and environmental factors that will slightly alter the mechanics of each kick, detailed analyses of each variable is beyond the scope of this needs analysis, as is analyses of other biomechanical skills that are used in football (running, jumping, landing, diving). For the purpose of biomechanical analysis, kicking a stationary ball can be broken down into four distinct parts; the approach, the standing leg, the kicking leg and the foot to ball contact (Lees, Asai, Andersen, Nunome, & Sterzing, 2010).
Generally, players will approach a stationary ball at an angle of 43-45° (Egan, Vwerheul, & Savelsbergh, 2007; Ioskawa & Lees, 1998) for two main reasons; firstly a curved path allows the body to be laterally inclined towards the centre of rotation which allows greater knee extension and increased foot velocity. Secondly, a curved run is utilised for stability of the standing leg, aiding both consistency and accuracy (Lees, Steward, Rahnama, & Barton, 2009). In addition to the curved run up, Lees and Nolan (2002) noted that the final step is greater when players are kicking maximally, which they associated with a higher degree of pelvic retraction and higher range of pelvic rotation needed to produce a maximum velocity kick.
Kellis, Katis & Gissis, (2004) studied the ground reaction forces of the support leg of ten amateur players in three angles of approach; vertical (15-20 N.kg-1), posterior (4-6 N.kg-1) and lateral (5-6 N.kg-1). This study – amongst others – concluded that horizontal forces are usually directed in posterior and medial directions (Lees, Steward, Rahnama, & Barton, (2009); Orloff, Sumida, Chow, Habibi, Fujino, & Kramer. 2008). As the standing foot strikes the ground, Lees and colleagues (2009) found knee flexion to be positioned at 26° on average, with flexion increasing to 42° as the kick continues to ball contact. In addition, the same researchers reported flexion/extension moments of the ankle (2.2 N. m KG-1), knee (3.2 N. m KG-1) and hip (4.0 N. m KG-1). Kellis, Katis & Gissis, (2004) found that a higher angle of approach resulted in greater production of ground reaction forces both medially and posteriorly. In addition, the angled approach showed increased external rotation displacement and a greater pre-activation of biceps femoris when compared to a straight run up.
Muscle activation timing of kicking has been studied through the use of electromyography. The sequence of the kick is proximal to distal, with iliopsoas activating to produce hip flexion, followed by rectus femoris – which provides both hip flexion and knee extension – and lastly knee extensors such as vastus lateralis (Dörge, H. C., Andersen, T., Sørensen, H., Simonsen, E. B., Aagaard, H., et al (1999) in conjunction with ankle dorsiflexors such as tibialis anterior (Asami, & Nolte, 1983). A stretch shortening cycle occurs during the kicking action; the quadriceps contract eccentrically due to knee flexion as the thigh moves forwards from hip extension to hip flexion. As the forwards motion continues, the stretch shortening cycle occurs and the knee begins to extend through concentric contraction of the quadriceps (Lees, Asai, Andersen, Nunome, & Sterzing, 2010).
Anderson (1999) suggests that increased ball velocity can be achieved by either increasing foot velocity or by having more mass in the lower limb to kick with (Ball, 2008). Additionally; Bollens, De Proft, & Clarys, (1987) stress the importance of dorsiflexor rigidity for successful kicking, after their biomechanical analysis showed high activation levels of tibialis anterior. Nunome and collegues (2006) found that foot to ball contact is brief, lasting just 10 milliseconds. Ultra high-speed video has shown, that on impact, the foot is usually abducted (passively), everted and plantar flexed with the ability to produce up to 2,800 newtons of force (Shinkai, Nunome, Ikegami & Isokawa, 2008).
As the best professional teams continue to advance the physical capacities of players, data is showing that lower ranked teams tend to show physiological values similar to those reported 30 years ago (Stølen, Chamari, Castagna & Wisløff, 2005). The top national teams such as Germany have higher average VO2 max than the less well-ranked teams such as India and Singapore (Stølen, Chamari, Castagna, & Wisløff, 2005), similar research also found that players in league winning team in Hungary showed greater average aerobic capacities than the team that finished bottom (Wisloff, Helgerud, & Hoff, 1998) and in Iceland, where the top teams had superior peak oxygen uptake (63.2 ± 4.5 vs 61.7 ± 5.1 mL.kg -1 .min, p = 0.02, N = 226) (Arnason, Sigurdsson, Gudmundsson, Holme, Engebretsen & Bahr, 2004). Wisloff and colleagues (1998) also found a 13% difference in maximum oxygen uptake (a measure of endurance) and a 22% one-rep max of leg extensor strength between the top and bottom teams in an elite Norwegian league. This data suggests that to achieve a higher league position, the strength and conditioning coach should effectively train aerobic capacity effectively, taking positional variances into account (Wisløff, Castagna, Helgerud, Jones, & Hoff, 2004). In contrast to the differences seen in oxygen uptake, Arnason and colleagues (2004) reported few differences between the top teams and bottom teams in the two highest leagues in Iceland, after testing 306 players from 20 teams on body composition, jump testing, leg extensor power and flexibility. These findings may be attributed to a number of factors, firstly; the differences in player quality between these two leagues is unknown, also; the researchers tested players just one time - before the season had even started, the relationship to fitness and league position is therefore flawed as other variables could have skewed the results.
Football is a high intensity team sport, characterised by aerobic activity that is supplemented with intermittent bouts of anaerobic activity in the form of; kicking, rapid acceleration sprints, turns, jumps and tackles (Bangsbo, & Michalsik, 2002). Although the majority of the movement within a game will be of submaximal intensity (Reilly, 2000), mean work rate has been reported to be close to anaerobic threshold at approximately 70-75% of maximal work rate (Bangsbo, Nørregaard, & Thorsoe. 1991). The strength and conditioning coach should understand positional needs, as generally, midfield players, lateral defenders, central defenders, strikers and goalkeepers have vastly different energy expenditure requirements (Stølen, Chamari, Castagna, & Wisløff, 2005). When devising a periodization programme for an elite football player, it is crucial for the strength and conditioning coach to have a deep and research driven understanding of physiological, technical and biomechanical requirements needed to perform at the top level. In addition, an understanding of what separates an elite player from an amateur player is advised, as is the ability to test and interpret physical performance.
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