Skeletal and smooth muscles move when nerve impulses, sent from the stimulate the muscle fibers, telling them to either contract or relax.

Lots of points if answered ! match the terms to their definition. 1. physical stress a term used to describe the workload placed on the body in general 2. plateau a principle that refers to the gradual increase in the amount of exercise sustained over a specified period of time 3. progression how quickly your heart rate returns to normal after an activity session 4. recovery heart rate a principle stating that the results you get will be directly related to the type of work you do and to specific muscles or body parts being worked 5. specificity states that the body adapts to increasing demand by developing the ability to handle those specific demands 6. stamina the ability to sustain a workload for an extended period of time 7. the overload principle an element of fitness that is characterized by a decrease in improvement or a leveling off of performance