ACCELERATION SPRINT TRAINING EFFECTS ON ECCENTRIC HAMSTRING STRENGTH, SPRINT PERFORMANCE AND BICEPS FEMORIS FASCICLE LENGTH.

Acceleration is a pivotal quality in Australian football (AF); however, sprint-related hamstring injuries are the most frequent non-contact injury in AF. This case study aimed to determine the effects of an unresisted acceleration biased sprint training program on sprint performance, eccentric hamstring strength, and hamstring muscle architecture. One semi-professional AF athlete undertook 6-weeks of unresisted acceleration training during the off-season period of 2020. Unresisted acceleration training was completed twice weekly, over distances of 5-metres, 10-metres, and 15-metres. A variety of starting positions (2-point, 3-point, walking) were utilised to apply progressive overload. Sprint performance tests of acceleration (0-10m) and maximum speed (30-40m), alongside an eccentric hamstring strength assessment, and a Biceps Femoris Long Head ultrasound were completed before and after the intervention. Fascicle length and hamstring muscle soreness were recorded following each of the 12 training sessions during the intervention. Overall, the athlete improved across all areas of testing, with notable improvements in maximum speed (-7%), mean eccentric strength (+16%), and Biceps Femoris fascicle length (+9%). Furthermore, the reported soreness for the athlete was low, addressing a common barrier for speed and eccentrically biased training. This case study highlights that unresisted sprint training when programmed in line with best practice guidelines is an effective tool to improve sprint performance. The short time frame of adaptation is an encouraging aspect and supports the trainability of these qualities during a typical mesocycle. These findings offer an accessible, effective protocol, that can be modified to address common modifiable risk factors (eccentric hamstring strength and Biceps Femoris Long Head fascicle length) for hamstring strain injury, and simultaneously improve sprint performance. [ABSTRACT FROM AUTHOR]