ABSTRACT
Within the human body these forces can be further defined into being either external or internal forces. External forces include all the forces that exist outside of the body: such as in the case of kicking a soccer ball and internal forces include all those that act inside the body: such as the forces across the anterior cruciate ligament in the knee when a player is tackled in rugby. Often many of the external forces are responsible for the internal forces that are experienced by the muscles, bones, joints, ligaments, and tendons. Both external and internal forces act at various places all over the body during movement. Without the existence of these forces we would not be able to move with any acceleration. Similarly, to achieve a specific performance such as in the case of sprinting 100 m in less than 10 seconds requires the careful execution and control of force. However, such forces can also cause injury and a more thorough understanding of them will help in both the improvement in performance and future prevention of injury. Consider Fig. B1.1 and see if you can identify some of the different external and internal forces that are occurring in these activities.
