Physical activity can promote positive physical changes which, when performed repeatedly, can result in improvements to sport performance. However, activity that is too intense or too frequent may result in potential injury. Reducing injury occurrences and severity has shown to be critical for competitive success. In college football, injury rates have been reported to be 7.14 per 1,000 athlete exposures (AEs), with 35% occurring from a non-contact or overuse cause. A potential contributor to these injuries may be the length and intensity of sport activities that athletes experience following periods of time-off. Another contributor could be the rate that athletes experience this increased activity. In response, sport practitioners have begun measuring athlete activity during training and competition. Research has shown relationships between the amount of activity (workload), the rate of activity exposure, and ensuing non-contact injury. However, these studies have drawn criticism for how these relationships were assessed and the lack of an associated path between activity and injury. In response, the purposes of this dissertation were to 1) utilize modern techniques to assess the relationships among injuries, activity, and rate of activity increase at a particular point of the season between two different teams, 2) determine the non-contact injury rates for each phase of the calendar year and assess the relationship of injury occurrence to activity and activity rates within one team, and 3) to evaluate if inflammation may be a key component on the path between activity and non-contact injuries. Our first study measured workload, workload ratio, and non-contact injuries from two football teams (120 athletes) across two seasons. Both teams observed 44 total non-contact injuries, however the difference in reported injuries which resulted in time-loss from sport (Team 1: 6; Team 2: 17) led us to question if teams used different criteria for removing an athlete from team activities. Teams had different workload and workload ratios in each phase of the year. Our calculations demonstrated that workload and workload ratios were associated with injuries. However increased activity was associated with lower chance of injury, and workload ratios were only associated with a higher chance of injury to a point. These relationships were consistent with our second study, which examined these measures across nearly three years of data from one team (n = 88). The pre-season practice phase was the largest in both workload and time-loss non-contact injury rate (4.70 AEs), however, winter conditioning (2.84 AEs), spring practice (2.64 AEs), and summer conditioning phases (1.42 AEs) had injury rates higher than in-season (1.20 AEs). This suggests the need to monitor these other phases of training. Finally, we assessed C-reactive protein in 19 football players during a pre-season and in-season period to determine if workload and workload ratios led to increased inflammation (CRP), which led to non-contact injury. However, our study showed that CRP did not vary across time and was poorly related to any difference in activity from week to week. However, the observance of only one time-loss non-contact injury limited our findings. Overall, our studies highlight the strengths and weaknesses of the current workload and workload ratio research. Further research should be conducted across multiple teams and years in order to observe enough non-contact injuries to permit the use of certain statistical tools that would be more useful to practitioners and coaches. In addition, further research should continue to see if there is a path between seek to find mediating pathways between activity and injury.
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