5A 117 INCREASING WORKLOAD RELATES TO INJURY RISK IN RUNNING 3.4. Relative Risk and prediction Fortnightly and between week two and three the ACWR difference category ‘Low increase’ was associated with the risk on sustaining an injury. The runners sustaining an injury with the fortnightly ACWR difference category ‘Low increase’ had a RR of injury of 4.49 (CI 95%: 2.02 – 9.96, p < 0.000). The relative risk for sustaining an injury with the weekly ACWR difference category ‘Low increase’ between week two and three was 2.74 (CI 95%:1.30 – 5.76, p = 0.012). In terms of percentage, the ACWR difference category ‘Low increase’ is overrepresented in the four-week period before the injury in comparison with the periods not preceding an injury. Figure 2 illustrates the distribution of the fortnightly AWCR difference categories comparing the period before the injury with the period without injuries. The predictability of an injury expressed by the specificity and sensitivity is limited. The fortnightly AWCR difference category ‘Low increase’ has specificity of 0.62 and a sensitivity of 0.74. Where the AWCR difference category ‘Low increase’ between week two and three has a specificity of 0.57 and a sensitivity of 0.68. 4. DISCUSSION The current study expressed the workload in running as the combination of duration and RPE and investigated the association between the acute workload, the chronic workload, the ACWR, the change in the ACWR and the injury risk in competitive runners. We did not find an association between the acute workload, the chronic workload, the ACWR and injury risk. However, a 4.5-fold increase in injury risk was associated with low increase (0.10–0.78) of the fortnightly AWCR difference. Also, a 2.7-fold increase in injury risk was demonstrated for a low increase (0.05–0.62) of the week-to-week ACWR difference between week three and two before an injury. These findings suggest that there is an association between increased ACWR and the risk of sustaining an injury. The injury incidence of 3.6/1000h was comparable to previous studies on competitive runners that found incidences from 2.5–7.4 injuries per 1000 h for long-distance runners [35], [36] and 5.6–5.8 for sprinters and middle-distance runners [36]. Conform literature most injuries in the current study were reported in the calf-Achilles region [23], [27]. A main difference between the literature on running and injury risk and this study is the definition of workload. Previous studies in running defined workload as a single nonrelative factor, like duration, distance, or frequency [4,6,7], whereas we applied a combination of duration and RPE, the sRPE [23]. The sRPE was expressed in acute and chronic workload. The current research did not show an association between acute or chronic workload and injury risk. Based on the literature on running one cannot draw a conclusion on the relationship between a single nonrelative workload factor and
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