Possible mechanisms of muscle cramp from temporal and spatial surface EMG characteristics

In this study, the initiation and development of muscle cramp are investiga ted. For this, we used a 64-channel surface electromyogram (EMG) to study t he triceps surae muscle during both cramp and maximal voluntary contraction (MVC) in four cramp-prone subjects and during cramp only in another four c ramp-prone subjects. The results show that cramp presents itself as a contr action of a slowly moving fraction of muscle fibers, indicating that either the spatial arrangement of the motoneurons and muscle fibers is highly rel ated or that cramp spreads at a level close to the muscle. Spectral analyse s of the EMG and peak-triggered average potentials show the presence of ext remely short potentials during cramp compared with during MVC. These result s can also be interpreted in two ways. Either the motoneurons fire with enl arged synchronization during MVC compared with cramp, or smaller units than motor units are active, indicating that cramp is initiated close to or eve n at the muscle fiber level. Further research is needed to draw final concl usions.