An exploration into the assessment of hip extension strength and its importance for performance in professional soccer.

Field: Health Professions (Health Sciences)

Hip extension is a joint action that contributes to athletic movement during performance in various sports. Within the sport of professional soccer, high intensity efforts encompass an important proportion of athletic movement and optimal hip extensor functioning can be seen as a crucial action for the successful performance of such actions. Perhaps related to the importance placed upon high intensity efforts in soccer, the number of hamstring strain injuries that occur are of major concern to practitioners within the field. As such, great efforts are made to establish methods of managing and mitigating these injuries, one of which being improving hip extension function. Methods of establishing an individual’s maximal hip extension strength capacity are available yet are not void of several clinical and practical limitations. As such, understanding the relationship between the specific ability of hip extension with performance and injury related measures are difficult to investigate. Therefore, it may be of use to investigate the development of new strength assessment methods. In study 1 (chapter 3) a framework of considerations was outlined that surround various methodological and theoretical concepts believed to influence the subsequent validity, reliability and operational success of hip extension assessment tools in the applied field. These considerations arose from information in previous scientific research and from the research team’s (PhD candidate and supervisors) wealth of experience working in applied professional sport. Throughout the framework of considerations, the assessment tools currently available for hip extension strength were critiqued and a rationale for the development of a new tool was outlined. Further into the chapter the adherence of these considerations was presented throughout the development of a new assessment tool (Hip Extension Bench). Finally, the ultimate section of this chapter then introduced information surrounding practical application of the Hip Extension Bench. In study 2 (chapter 4) the sensitivity of the Hip Extension Bench was investigated where the research team assessed muscle activity and force changes in response to various hip flexion positions. The investigations were undertaken with a mixed population of elite soccer players (n = 10), competitive sprinters (n = 10) and recreationally active males (n = 5) and consisted of assessment across 6 different hip positions (70, 60, 45, 30, 15 and 0 hip flexion). Results displayed precise and specific changes in individual hip extensor muscle activity and force production under maximal isometric contractions at different hip joint angles. Gluteus maximus muscle peak activity was pronounced at positions of inner range hip flexion (0 and 15) whereas maximum force and biceps femoris long head and semitendinosus peak activity was pronounced at positions of greater hip flexion (60 and 70). These data suggest that the Hip Extension Bench can be manipulated to selectively target specific hip extensor muscles and careful precisions must be adhered to upon assessment setup to confirm standardised conditions. In study 3 (chapter 5) the test-retest reliability of the Hip Extension Bench under non-fatigued conditions was investigated. A group of 40 elite youth soccer players and 15 competitive sprinters undertook maximal isometric hip extension contractions at two angles (15 and 60) on two occasions with a minimum and maximum of 7 and 14 days between test days. Generally, both cohorts demonstrated good reliability of bilateral and unilateral isometric hip extension strength assessments. The findings also demonstrated the difficulties surrounding data collection in the applied field where several complications may arise that influence the subsequent findings and informed decisions that are made on reflection of the data. In study 4 (chapter 6) the first implementation of the Hip Extension Bench within research surrounding isometric hip extension strength and sprint-acceleration and jump performance associations was presented. A sample of 10 competitive sprinters completed a minimum of three 40 m sprints on test day 1 and a comprehensive battery of strength and power assessments on test day 2 with a minimum and maximum of 7 and 14 days between each test day. The main findings confirmed that isometric hip extension strength was highly correlated with several force-based variables of sprint-acceleration performance (theoretical maximum force; F0, total force; FT Peak, total force across distances of 2, 20 and 40 m; FT 2, 20 & 40 m, mean horizontal force; FH Mean, horizontal force across distances of 2 and 20 m; FH 2 & 20 m and peak power; Pmax) and jump performance in the horizontal direction (the sum of left and right leg horizontal countermovement jumps; UL HCMJ Sum). These findings provide evidence for the role and importance of hip extension strength, specifically under isometric conditions, in high intensity effort performance. Overall, these findings suggest that a new assessment tool for isometric hip extension strength has been developed that is suitable for application in the environment of applied professional sport. The findings also confirmed the important of hip extension for high intensity effort performance and in conclusion provide a strong rationale for the implementation of the Hip Extension Bench for future research and application in performance and injury management.