KINEMATIC FACTORS AFFECTING FAST AND SLOW STRAIGHT AND CHANGE-OF-DIRECTION ACCELERATION TIMES

Hewit, JK, Cronin, JB, and Hume, PA. Kinematic factors affecting fast and slow straight and change-of-direction acceleration times. J Strength Cond Res 27(1): 69-75, 2013-In many sports, players are often required to accelerate immediately after rapid changes of direction (CODs) before performing a subsequent COD movement. Therefore, court-based players will often not attain their maximum velocity before having to decelerate and change direction. The purpose of this study was to determine what kinematic factors affected fast and slow straight acceleration (SA) and change-of-direction acceleration (CODA) times. National under-21 netball players performed 3 trials each of a 2.5-m SA and a CODA involving a 180 degrees COD followed immediately by a 2.5-m sprint. Players were grouped into either a faster or slower category based on performance times (2.5-m time). Significantly higher average step frequency (4%, p = 0.03) was observed for the faster group when compared with the slower group in the CODA task. For the SA task, faster times were associated with significantly smaller average step lengths (SLs; 7%, p = 0.03), greater torso angles (i.e., greater forward lean; 30-37%, p < 0.001), and smaller hip angle (less knee lift) in the first step (21-22%, p = 0.00). The SA task was associated with significantly longer average SLs (21-23%, p = 0.00) and significantly longer SL across all 3 steps as compared with the CODA task (17-27%, p < 0.001) A significantly increased forward lean was associated with the first step of the SA task (34%, p < 0.001) and significantly higher knee lift for the first and second steps of the SA task (11-22%, p = 0.00 and 0.04, respectively). These kinematic differences can be used for training purposes for both coaches and strength and conditioning practitioners.