When you work harder, your muscle cells work harder and increase in size. how might various organelles in a muscle cell increase in size, number, or activity to respond to the challenge of an increased workload?

The muscle cells allow the body movement along with the skeletal system.  

After physical exercise, the muscle cell adapts either by an increase in cell number, increasing the diameter of the fibre and the increase in the cytosolic organelles which can increase the efficiency of the muscle cells.

The cells grow in number and size by adding the myofibrils to the existing cells and by adding sarcomeres to increase their length.

The physiological response is elevated by increasing the number of energy-producing organelle in the cell called mitochondria which produce ATP in response to the physical exercise.