One reason that electric power plants do not send out electrical energy as a direct current is that direct current can not be transformed explain why

This is because direct power has no pulsation (waveform characteristic) that is significant in electromagnetic induction. The gradual increase and decrease of power, at a given frequency, in indirect power is significant in electromagnetic induction. This enables transformers to induce electricity into the secondary coil, from the primary coil, at the core of the transformer.Transformers transform electric power by increasing or decreasing the voltage and current of electricity.

the answer is lactic acid from anaerobic respiration. the acid in lactic acid is what creates sore and burning muscles. if you think about how acid burns that will give you a clue for questions like this.