What term describes the external force acting on tissues causing internal reactions?

The term that describes the external force acting on tissues causing internal reactions is load. In the context of biomechanics and athletic training, a load refers to any force that is applied to a tissue, such as muscle, tendon, or ligament, which can lead to various internal physiological responses. These responses can include deformation of the tissue and changes in its mechanical properties, impacting its strength, flexibility, and overall function.

Understanding the concept of load is essential for athletic trainers and therapists, as it guides them in determining safe levels of activity for athletes and in designing rehabilitation programs that consider the tissues' reaction to stresses and strains resulting from loads. Consequently, recognizing how different loads affect tissues helps practitioners in preventing injuries and enhancing performance.

The other terms, such as stiffness, elasticity, and creep, are related concepts but do not directly describe the external force itself. Stiffness refers to the resistance of an object to deformation under load, elasticity denotes the ability of a material to return to its original shape after deformation, and creep indicates the time-dependent permanent deformation of a material under constant load. While these concepts are important in understanding how tissues respond to loads, they do not define the external forces acting upon them.