The Ability of Internal and External Workload to Predict Soft Tissue Injury of the Lower Limbs in College Female Soccer Players

Background: Understanding an athlete’s workload is one way to determine the likelihood of receiving a sports injury. Workload variables are categorized as either internal load (IL) such as heart rate, or external load (EL) which include speed, distance or volume. Objective: This study investigated the correlation between IL and EL measured by micro-technology in female college soccer players. In addition, the utility of IL and EL to predict risk of soft tissue injury on lower limbs was examined. Method: 23 NCAA Division One women soccer players 19.2 ± 1.2 years old, 168.2 ± 7.3 cm, and 141.0 ± 17.9 kg were recruited. Only field players with no prior lower limb injuries were included. IL measurements collected were ratings of perceived exertion (S-RPE), average heart rate (Avg-HR), training impulse (TRIMP i.e., HR x time) and estimated maximum heart rate (Max HR). Total distance (TD), average speed (Avg-Spd), high speed running distance (HSR), estimated maximum speed (Max speed) and intensity volume index (VI index) were identified as EL. The workload data were categorized as being either acute or chronic. Acute was defined as the measured average workload the seven days immediately prior to the injury, while chronic workload meant the average workload 21 days before the athletes were hurt. Spearman correlation was used to examine the relationships between IL and EL and one-way ANOVA and Kruskal Wallis tests were conducted to investigate the mean differences between injury groups. Results: There were significant positive correlations between S-RPE and TD (r = .82, p < .001), TRIMP and TD (r =.75, p < .001), Avg-HR and Avg-Spd (r = .80, p < .001), and H-HR zone and HSR (r = .60, p < .001). The results indicated that the acute Avg-HR, the A/C ratio of Avg-Spd and VI index were significantly (p = .001) higher in the injured compared to the non-injured group. Conclusion: The study indicated that internal and external load were significantly correlated in this group of female soccer players. Also, acute Avg-HR and A/C of speed and volume index may predict the risk of soft-tissue injury in female athletes.