IntroductionAcceleration is an essential component in many different field sports, including games such as rugby, soccer, American football and tennis (Spencer, Bishop, Dawson and Goodman, 2005). It is widely considered the most important attribute in team sports (Wilson, Lyttle, Ostrowski, & Murphy, 1995), so the ability to improve it would be valuable for many sporting events (Cronin & Hansen, 2006). An athlete's ability to accelerate depends on numerous factors, including technique/body position (kinematics) and the force production capacity (kinetics) of the body (Cronin, Hansen, Kawamori, & McNair, 2008). Important kinematic factors that influence acceleration performance include stride frequency and length (Hunter, Marshall, & McNair, 2004; Murphy, Lockie, & Coutts, 2003), stance phase duration (Murphy Lockie & Coutts, 2003), the position of the foot strike through the athlete's center of mass (Chu and Korchemny, 1993), the knee flexion angle before and after the foot strike (Murphy, Lockie and Coutts, 2003), the amount of hip extension at takeoff (Vonstein, 1996), the take-off angle of the athlete's center of mass at takeoff (Hay, 1985) and trunk inclination that progressively decreases from 45⁰ to 5⁰ (Baechle and Earle, 2008). Kinematic factors, particularly trunk flexion, may change slightly as an athlete becomes fatigued, as trunk muscle fatigue has been shown to cause increased trunk flexion during running (Hart, Kerrigan, Fritz, & Ingersoll , 2009). Koblbauer, Schooten, Verhagen, and Van Dieen (2013) found that an increase of just 4⁰ in trunk flexion during running in novice athletes can increase the risk of injury to the lower extremity and back muscles by exposing the knee to a greater load (Z.... .. middle of paper ......ervention. Furthermore, future research needs to identify whether the small change in trunk flexion found in this study could lead to long-term effects on trunk kinematics sprint. This will allow coaches to understand how weighting vests can impact sprint kinetics and how it can be manipulated to increase acceleration power and decrease the risk of injury trunk flexion at 5%, 7.5% and 10% (p = 0.83) resistance in resistance vest sprint training compared to unloaded sprinting The study highlights that low percentages of sprint resistance do not cause injury through the change in trunk kinematics, although trunk flexion is increased slightly in response to an external stimulus, recent research (Koblbauer, Schooten, Verhagen and Van). Dieen, 2013) suggests that this increase is not enough to raise concern about injuries.