We computed the coherence function between simultaneously recorded endogenous skeletal muscle vibrations (vibromyogram, VMG) and electro‐cortical oscillations (electroencephalogram, EEG) in man in order to demonstrate a functional coupling of these signals. For detection of transient changes in coupling strength a novel computerized technique for calculation of the ‘running’ coherence was developed. High coherence values indicated a deterministic relationship between VMG and EEG. Cyclic variation in coherence with periods of 20–70 sec (mean value of 40 sec +/‐ 9 SD) demonstrated an ordered temporal pattern of changes in coupling strength between brain and muscle rhythms. The data suggest the existence of a common rhythm generator involving various oscillating structures, which may simultaneously drive supraspinal cortical and spinal segmental CNS activity. The same source may in part also be responsible for some autonomic rhythms. Models explaining the cyclic variation in VMG‐EEG coherence and a clinical concept of temporal disorder as ‘disease’ are discussed.