# Impact of One Additional Substitution on Player Load and Coaching Tactics in Elite Football
## 1 Introduction  
The demand for additional substitutions in football has been raised by professional players, coaches, and recent scholarship [1, 2]. This has been supplemented by research findings confirming reduced player performance in extra time [3, 4]. Players of the top clubs and national teams have reported an ever-increasing strain due to both an increased speed of play during matches and an increased frequency of matches [5, 6]. More competitions and less regeneration time have been identified as the prime sources of increasing injury frequency [7]. In order to counteract this increased burden, the International Football Association Board (IFAB) allowed an additional substitution during extra time of professional football matches in 2016 [8]. Information about the impact of this rule change on the game has largely remained limited [2, 9]. Therefore, this study evaluates the effects of an additional substitution in regular time and extra time on the aspects of player load reduction and increase of tactical influence of coaches on the match. The additional substitution in extra time analysed in this study was approved by the IFAB and the Federation Internationale de Football Association (FIFA) in 2016 [10]. This rule change was specifically enacted by the IFAB to address the concerns of the global football community [8]. Recent scientific findings have indicated reduced player performance in extra time, which may have led to the requests making way for this rule change [3, 4, 11]. This aspect becomes particularly important in the light of the study [PERSON] et al. [4], who found that there had been an increasing number of matches with extra time at recent World Cup finals. Since 1986, more than one-third (35%) of senior FIFA World Cup knockout matches have required 120 min of match-play [4]. Therefore, substituting a player with better physical performance than a starting player has a positive impact on the game [12; 13]. Higher load causes not only a decrease in performance but also increases the potential for injuries. Despite this, the physical stress on athletes at the national level has increased over the recent years. This is caused by the higher speed of the game as well as the greater number of matches played per season [6]. The combination of higher load and less regeneration time has caused an increased frequency of injury for players [7]. The majority of coaches in football consider substitutes important for success during a football match, despite the limited influence that coaches have in reducing player load and changing their starting line-up or substitutions [14]. Substitutions can have a significant impact on a game of football, and the tactical influence of coaches on the match has been demonstrated in several studies [9; 15; 16]. For example, [PERSON] [13] concluded that both the substitutes and the substituted players scored more goals than players who were used for the entire duration of the game. Previous research has also indicated the physical advantages of using substitutes; namely, they cover greater distances with high-intensity [17; 18] and medium-intensity runs [19] than the players who have been in the game from the start [20]. This is in line with the practical perception by the coaches who state the main justification for substitutions being the perceived ability of these players to have a physical and tactical impact [15]. Overall, substitution behaviour is dependent during the course of the match on factors such as score and injuries [9; 14; 21]. There are several studies that suggest the best possible timing of substitutions using various approaches such as modelling the effect probabilities on match outcomes; none of them focus on improving the understanding of how the timing of substitutions influences the management of player load [22; 23]. In order to assess the impact of substitutions, it is relevant to study physiological conditions such as variations in exercise intensity and fatigue among football players.