## 4 Discussion  
This novel study examined the positional movement demands associated with participation in an NFL football game and is the first to report on position-specific loads on professional football athletes. Positions have different roles to play during a game and different locomotor demands required of their role. Significant positional differences with respect to total distance, maximum velocity, high-velocity movements, and acceleration and deceleration actions were identified. In addition, similarities in locomotor demands were found between positions that compete against each other during gameplay. For example, the highest total running volume and maximum velocity were observed in WR on offense and defensive backs (CB, S) on defense. Conversely, linemen (OL, DL) performed the least amount of running and exhibited the lowest maximum velocity compared to other positions. High-velocity efforts, acceleration, and deceleration efforts displayed variability between positional groups, suggesting movement activity is dependent on the in-play requirements for each group. Collectively, in addition to describing the locomotor demand of American football, these findings are relevant to practitioners who are responsible for physically preparing athletes for competition. The primary findings of this paper corroborate those of prior studies conducted on game play in lower levels of American football. In collegiate football matches, wide receivers and defensive backs performed the highest amount of total distance compared to other positions [3]. Similar observations were made at the high school level, where non-linemen positions accumulated greater total distance than linemen [19]. While such trends were observed to be consistent across levels of play, the average total game distance in this study was lower from that of [PERSON] and colleagues [3]. This difference might be because [PERSON] et al. tracked players while they were on the  
Figure 3: Distribution of (**A**) acceleration efforts, (**B**) acceleration distance, (**C**) deceleration efforts, and (**D**) deceleration distance accumulated by an NFL player during a regular season game based on position group. Horizontal lines represent the 25 th, 50 th, and 75 th percentiles, and the diamond denotes the average value for each position group. sideline as well as on-field, while this analysis only recorded on-field locomotor activities. Additionally, they quantified demands of a single collegiate team over one season, and their findings may be specific to how that team was coached; this research observed the demands of all NFL teams over multiple seasons. This could also explain the high variability within positions in this study. Teams compete with different tactical schemes depending on how they are coached, which could affect a player's in-game demands. The team's success or failure to execute in a game could also affect the metric, as teams with many scores and therefore many kickoffs may accumulate more distance at higher velocities. Participation levels may also contribute to the positional variability. Some players are starters and participate in most of a game's offensive or defensive plays, while others may only substitute in for a handful. Additionally, players may primarily participate in special team plays, which may also contribute to the positional variability. This study did not assess variability within position groups; further work should be undertaken to delineate the nuances of these tactical schemes and situations. Linebackers were observed to have the highest number of high velocity efforts (5.1 \(\pm\) 4.3); however, this group also displayed the largest variability across player-games. These findings may be specific to the unique roles LB perform on the field; some primarily serve to rush the QB, others are required to play in space and cover offensive players in the passing game, and still others may be used primarily to stop running backs on rush plays.