Evidence-based classification - Impact of including the ball in classificationNews
How does the ball influence the performance of change of direction and sprint tests in para-footballers with brain impairments? Implications for evidence-based classification in CP Football
Football is a multi-faceted sport, in which conditional, technical and tactical factors interact , requiring intermittent high-intensity efforts  where players are often required to repeatedly produce maximal or near maximal sprints of short duration (1–7 s) with brief recovery periods . The ability of soccer players to continually perform high-intensity high-speed actions is known to impact football match performance, defined as actions requiring rapid accelerations (10 m sprint), actions at maximum speed (30 m sprint), or actions requiring agility . Sheppard and Young  defined agility as a rapid whole-body movement with change of velocity or direction in response to a stimulus, but this definition comprises both a perceptual decision-making process and the outcome of this process, a change of direction (COD) or velocity . COD can be described as the ability to change direction while sprinting over a pre-planned course , so linear and change-of-direction speeds are essential qualities for athletes who play field sports such as football [7, 8]. Physical match analysis showed that during elite-level football games, players perform a considerable amount of COD bouts at high intensity using a wide range of turning angles , and straight sprinting speed has been also considered as a factor in the football-specific component model of COD .
Cerebral palsy (CP)-Football is a para-sport for athletes with brain impairments such as ataxia, hypertonia or athetosis (i.e. cerebral palsy, stroke or traumatic brain injury), and those impairments that might be deemed severe enough to impact on the performance of football skills. CP-Football is currently governed by the International Federation of Cerebral Palsy Football (IFCPF), with international tournaments organized by IFCPF (i.e. Continental championships, World tournaments and U-19 championships) and by the International Paralympic Committee (IPC) or its Regional Organizations (i.e. Paralympic Games, ParaPanAm Games, Asian Paragames, or European Paragames). Considering this high international repercussion, CP footballers deserve special attention. For a particular competition, players are classified in one of the following four profiles : i) FT5 athletes with hypertonia or spasticity in both lower limbs and to some degree in both upper limbs. These players have difficulty running, turning and stopping because of a lack of lower limb control; ii) FT6 athletes are affected by coordination and balance problems in all four limbs and trunk, and typically have difficulties dribbling the ball when running, accelerating and stopping; iii) FT7 class is designated for athletes with unilateral spasticity, meaning that only one side of their body is affected, causing the players to walk and run with a limp. On the impaired side the athlete might have problems balancing, so that often the impaired leg is used to kick the ball; and iv) FT8 describes the minimum impairment criteria to be eligible and it is usually difficult to see the impact of impairment when watching the player running or controlling the ball. However, involuntary muscle contractions and hesitation before explosive movements do constitute activity limitations in comparison to regular football players.
Paralympic classification systems aim to promote participation in sport by people with disabilities by minimizing the impact of impairment on the outcome of competition , placing athletes in the same class when their impairments cause a similar degree of activity limitation . Unfortunately, the system used for assessing and classifying brain impairments is typical of many Paralympic classification systems in which there is little scientific evidence on which to base methods for allocating these classes . Evidence-based classification research is currently a hot topic in Paralympic sports and, in particular, evaluation of sprint ability has been recently applied in wheelchair propulsion in athletics [15, 16], runners with prosthetic legs , runners with brain injury , wheelchair rugby , or CP-Football . The study by Reina et al.  demonstrated the validity and reliability of two COD tests to evaluate activity limitation in CP-Football players compared with controls. In fact, to the authors’ best knowledge, no previous studies have been focused on studying sprint and COD in para-footballers, comparing their performance with and without dribbling a ball.
Even though football requires accelerations, decelerations, and COD throughout the game, many sprints and COD tests are conducted around stationary objects. Whereas sprint running or pre-determined COD can be pre-planned (closed skill) , the inclusion of the ball during the test might increase its ecology . For example, straight sprints in football are mostly conducted with the ball and it is the most frequent action in goal situations . According to the new International Paralympic Committee Athlete Classification Code , International Sport Federations must develop sports-specific Classification Systems through multidisciplinary scientific research. Thus, it is necessary to evaluate general and specific football skills with standardized tests, in order to evaluate players´ activity limitations due to their impairments in a particular para-sport.
The aims of this study were: i) to analyze the absolute and relative intra-session reliability of three tests that require sprinting, accelerations, decelerations and COD (with and without ball) in para-footballers with brain impairments; ii) to evaluate the relationships among the tests used in the study; iii) to compare the performance in the tests when ball dribbling is required; and iv) to explore the practical implications for evidence-based classification in CP-Football and its usability for decision-making with the current classes. Hence, we hypothesized that the proposed tests to assess performance in CP-Football players will exhibit good intra-session reliability, being useful for decision-making between current class profiles. In addition, dribbling a ball during the tests will constrain para-footballers performance, requiring higher time to complete the tests.