Reliability of forearm muscle electromyography data during multi-planar maximum voluntary contraction grip and wrist articulation

INTRODUCTION
To date the Myon 320 system has yet to be reliably tested using forearm muscles responsible for gripping. The purpose of this research is to reliably test electromyographic (EMG) signals from both right and left Flexor Digitorum Superficialis (FDS) and Extensor Carpi Radialis Brevis (ECRB) muscles during an individual, static multi-planar maximum voluntary contraction (MVC) hand grip task. According to Ratamess et al, (2007) pulling exercises such as dead lifts, bent over rows, and pull-ups all greatly depend on the athlete’s level of grip strength. Therefore, resistance training to improve grip strength may be critical to athletic success in several sports. Friden and Lieber, (1994) suggest that very high tension levels in the ECRB muscle maybe a causative factor in lateral epicondylitis. This corresponds to the secondary findings of the study that there was a significant increase in output from the ECRB in comparison to the FDS.

METHODS
Eight right handed male subjects participated in this pilot study. (Age: 22.5 ± 7.6 years, Height: 185.5 ± 5.40cm, Weight:82.18 ± 29.69 kg). Participants were attached to a custom rig (to ensure correct elbow positioning). A Myon 320 Surface EMG System was used with AMBU surface electrodes to capture the output of the ECRB and FDS during each MVC. A Medical Research Ltd pinch grip digital analyser was used to capture the force (N) of each maximal hand grip for a maximum time of five seconds. A total of ten trials were carried out for each hand with five separate wrist positions (neutral, flexion, extension, radial deviation and ulnar deviation) and two repetitions per position. All data was captured by a Myon 320 Surface EMG system where a high/low pass Butterworth filter and RMS were implemented prior to analysis. All data was then imported into Microsoft Excel 2016 where the Mean, Standard Deviation, Standard Error of Means were calculated for all outputs. A Paired T-Test was also carried out to compare the differences between the four muscles (left and right FDS, ECRB) and their corresponding wrist positions. Significance was set to P = 0.05.

RESULTS AND DISCUSSION
There were no significant differences (P>0.05) shown between both left vs right FDS and left vs right ECRB. However, a significant difference was displayed across different muscle groups (left FDS vs left ECRB and right FDS vs right ECRB). This increase is visible across all five wrist positions. The ECRB muscle displayed an average of 3.3 times the output of the FDS (SD ± 0.49). This concurs with Snijders et al. (1987) who suggest that a power grip is associated to the high loading of extensor muscles. It has also been noted that this increase was not only significant with the wrist in the extension position, but also in neutral and flexion. Again, Snijders et al. (1987) support these findings by commenting that the grasping hand in the fingers cause a flexing moment at the wrist joint in various situations, which must be equilibrated by the activity of the extensor muscles.

CONCLUSIONS
The results of this study have clearly shown that there is no significant difference in EMG output across either the FDS or ECRB when comparing the same muscle on both left and right side during different wrist positions. There is however a significant difference when comparing the FDS against the ECRB on the same arm. This pilot study concludes that the data retrieved from all participants have been validated and these protocols, methods and system can be used in future trials.

ACKNOWLEDGEMENTS
The authors would like to thank staff at the University for their support throughout the study and the participants for their patience and professionalism. The staff at Myon are also acknowledged.