PHASE FOUR- ACCELERATION

The acceleration phase is concerned with the initial steps out of the blocks as the athlete drives into a full upright running position. In these first strides, the body moves like an arrow at 45 degrees. They are short fast and low strides with a rapid foot action off the ground. Each stride should lengthen as the body becomes upright. The gaze assists in the change in truck angle as the eyes follow the ground until in a full running action (Fig 5) (Ballesteros 1979).

Fig 5
Picture sourced 23-4-13

 Biomechanical Principles

During the block start the athletes centre of gravity is shifted forward of the driving foot as the body and the trunk leans forward (Brynes 2012). Dyson explains that athletes needs to constantly change their trunk lean and centre of gravity in relation to the supporting foot to gain maximum acceleration through an extended back leg. Each stride out of the blocks an athlete needs to raise their centre of gravity to a full up right running position. In terms of angular kinetics the speed of legs is vital for the speed of running. Speed or torque is created through the hip flexibility and leg strength. Also the legs work as levers as they cycle or rotate through the four phases of the running action (Blazevich, 2010 p77).  Like the block start the running action also has a four phases, contact, support, drive, recovery (fig 6). The drive and recovery phases are the most important when considering the acceleration out of the block start. At the drive phase the back leg is pushing off the ground to propel the body forward and the recovery phase is where the leg is preparing for the subsequent stride.

Fig 6
Picture sourced 23-4-3 http://www.oandplibrary.org/popup.asp?frmItemId=E430377C-3232-400F-8BDE-F481D84ECA38&frmType=image&frmId=24