When you do a shuttle run , you can be said to be close to executing simple harmonic motion. Running back and forth two fixed points , you probably have strained your knees at the two extreme ends and running through the centre with not effort at all. This describes the acceleration as the force is proprotional to acceleration F= ma. The important thing to remember is that the acceleration is not constant having maximum magnitude at the two ends and zero in the centre, always directed towards the centre. The direction of acceleration towards the centre simply means that if you are running away from the centre you will have to slow down as your direction of motion is opposite to acceleration . If you are running towards the centre you accelerate because the direction of motion is in the same direction as acceleration.The next step is to know all the formulas needed to calculate acceleration , veloctiy and whatever time or displacement.
