Final answer:
Isometric contractions do not change the angle of a skeletal joint and involve sarcomere shortening and increasing muscle tension, but do not move a load. They are active in maintaining posture and maintaining bone and joint stability.
Step-by-step explanation:
An isometric contraction occurs as the muscle produces tension without changing the angle of a skeletal joint. Isometric contractions involve sarcomere shortening and increasing muscle tension, but do not move a load, as the force produced cannot overcome the resistance provided by the load.
In everyday living, isometric contractions are active in maintaining posture and maintaining bone and joint stability. However, holding your head in an upright position occurs not because the muscles cannot move the head, but because the goal is to remain stationary and not produce movement.
Most actions of the body are the result of a combination of isotonic and isometric contractions working together to produce a wide range of outcomes.