Athlete Acceleration and Its Effect

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Introduction
Acceleration 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 and Murphy, 1995), therefore the ability to enhance it would be valuable to many sporting events (Cronin and Hansen, 2006). An athlete’s ability to accelerate is dependent upon numerous factors, including technique/body position (kinematics) and the force production capability (kinetics) of the body (Cronin, Hansen, Kawamori and McNair, 2008). Important kinematic factors that affect acceleration performance include step frequency and step length (Hunter, Marshall, and McNair, 2004; Murphy, Lockie and Coutts, 2003), duration of the stance phase (Murphy Lockie and Coutts, 2003), position of foot strike through the athlete’s centre of mass (Chu and Korchemny, 1993), knee flexion angle before and after foot strike (Murphy, Lockie and Coutts, 2003), the magnitude of hip extension at toe-off (Vonstein, 1996), the angle of take-off of the athlete’s centre of mass at toe-off (Hay, 1985) and trunk lean progressively decreasing from 45⁰ to 5⁰ (Baechle, and Earle, 2008).
Kinematic factors, in particular trunk flexion may change slightly when an athlete fatigues, as fatigue of the trunk musculature has been shown to cause an increase in trunk flexion during running (Hart, Kerrigan, Fritz and Ingersoll, 2009). Koblbauer, Schooten, Verhagen and Van Dieen (2013) found that an increase of just 4⁰ trunk flexion whilst running in novice athletes can increase risk of injury of the lower limbs and back musculature by exposing the knee to increased load (Z...

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...ervention. Furthermore future research needs to identify if the small change in trunk flexion found in this study could lead to any long term effects on sprint kinematics. This will allow coaches to understand how weighted vests may impact on sprint kinetics and how it can be manipulated to increase acceleration power and decrease risk of injury.
In conclusion there was no significant difference in trunk flexion at 5%, 7.5% and 10% (p=0.83) resistance in resisted vest sprint training compared to unloaded sprinting. The study highlights that low percentages of resisted sprint resistance will not cause injury through change in trunk kinematics. Although trunk flexion did increase slightly to the response of an external stimulus, recent research (Koblbauer, Schooten, Verhagen and Van Dieen, 2013) suggests this increase is not enough to cause concern for injury.

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