Tetany is a medical condition in which the frequency of action potential of muscles increases due to low blood calcium levels. The hypocalcemia is a primary cause that increases muscle contraction that causes spasms of the hands and feats. If the calcium levels in blood plasma are less than 50%, the contraction of muscles spontaneously generated that is it becomes involuntary. The low levels of parathyroid hormones can also cause tetany.

Fatigue is the feeling of overtiredness with extremely low energy. Muscle fatigue is the decline in ability of muscles to generate force. It can be a result of vigorous exercise, but abnormal fatigue may be caused by barriers to or interference with the different stages of muscle contraction.