Spatial summation is the recruiting of new muscle fibers to increase the muscle strength. Temporal summation occurs when a muscle fiber is continuously stimulated to contract without being able to conclude relaxation.
The permanence of a muscle fiber under a continuous state of contraction by temporal summation is known as tetany (e.g., the clinical condition of patients contaminated by the toxin of the tetanus bacteria). Tetany ends when all available energy for contraction is spent or when the stimulus ceases.