2011 Volume 9 Issue 2 Pages 147-151
Many forearm muscles are responsible for producing a gripping force and the interaction of EMG activity in forearm muscles is unclear during gripping. The purpose of this study was to investigate the change in EMG activity in forearm muscles during sustained gripping. Six subjects participated in this study. They performed sustained gripping with their dominant hand at 50% maximal voluntary contraction (MVC) and MVC without restriction of the wrist (maximum one minute). Gripping force and EMG (flexor carpi ulnaris [FCU], flexor digitorum superficialis [FDS], and extensor carpi radialis [ECR]) were measured simultaneously and average gripping force, root mean square EMG (rmsEMG) and mean power frequency (MPF) every five seconds were calculated. The relationship between contraction time and EMG responses (coefficient) were investigated. Fatigue was defined as a 5% decline in gripping force from the target level during 50% MVC. In 50% MVC protocol, there was no difference in the coefficient of rmsEMG among the three muscles. But, the coefficient of MPF was different and decreasing MPF in ECR tended to be smaller than in FCU. Only the coefficient of MPF in ECR tended to correlate with time to fatigue. In MVC protocol, the coefficient of rmsEMG was different and a decreasing rmsEMG in ECR tended to be larger than in FDS. There was no difference in the coefficient of MPF among the three muscles. These results suggest that neural drive to ECR is larger during gripping. Therefore, we conclude that EMG activity of ECR plays an important role in gripping.
