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Related to Infradian rhythm: ultradian rhythm
See: regularity
References in periodicals archive ?
Humans also exhibit rhythms shorter than 24 hours, termed ultradian rhythms, and longer than 24 hours, termed infradian rhythms (Refinetti & Menaker, 1992).
A cycle including a shorter interval, one less than 20 hours, is referred to as ultradian; infradian rhythms have a "repeat" that is greater than 28 hours.
The fact that they are only slightly smaller suggests the presence of a partially chaotic process mingled with more constrained processes such as circadian, ultradian, or infradian rhythms (Peters, 1991).