Isotonic exercises involve moving your joints and muscles rhythmically and repetitively through their ranges of motion using low resistance, while isometric exercises are static and require you to contract your muscles without joint motion.
Substations are normally outdoors and are enclosed by a wire fence. However in residential or high density areas, the substation may be indoors and housed inside a building to restrict the humming noise of the huge transformers. slide 2 of 6 View of a Substation
FIG. 1 is a diagram of a power substation 10 having a variable frequency transformer 12 to convert the power from one power grid 14 (shown in the figure as high voltage lines) coupled to the substation to another power grid 16 (shown has high voltage lines) coupled to the substation.