biorhythmics
/ˌbʌɪə(ʊ)ˈrɪðmɪks/noun
With singular concord. The biorhythmic properties of a person or other living organism; the study of biorhythms, specifically the use of one's own biorhythms for the purposes of self-improvement.
Origin
1940s; earliest use found in Acta Psychiatrica et Neurologica Supplementum. From biorhythmic: see -ic.