Answer: C. Improved joint flexibility
Explanation:
Isometric exercises are the exercises which involves the contraction of particular muscles or group of muscles. In these exercises the muscles do not change their length and the joints does not move. These are the exercises which are done in one position. These exercises are performed in order to obtain strength during training exercises during which the muscle length and joint angles do not basically change. These exercises are high intensity exercises and contributes to the building of muscles and burning of fat.
On the basis of the above information, A. Rapid strength improvement is the correct option.