The influence of wrist posture on the time and frequency EMG signal measures of forearm muscles

Abstract

This study investigates how altering wrist posture influences the relationship between the time and frequency measures of the electromyography (EMG) signal of extensor digitorum communis (EDC) and flexor carpi ulnaris (FCU). Thirteen participants exerted handgrip force related to maximum voluntary contraction (MVC) in four tests: 20%MVC and 50%MVC in neutral wrist posture and 20%MVC in full wrist flexion and extension. EMG measurements from EDC and FCU were used to calculate normalized values of amplitude (nRMS) and mean and median frequency of the power spectrum (nMPF, nMF). During muscle shortening (wrist flexion for FCU and wrist extension for EDC) nRMS was approximately twofold higher than in neutral posture for FCU and fourfold for EDC. All measures obtained at 20%MVC in neutral posture were significantly different from 20%MVC in wrist flexion for FCU and 20%MVC in wrist extension for EDC (p<0.05). Differences between 50%MVC and 20%MVC at neutral posture (nRMS) were significant for both muscles, although in nMPF and nMF for EDC only. Muscle shortening changed the pattern of statistical significance when the time and frequency domain measures were compared, whereas muscle lengthening did not. It can be concluded that muscle shortening caused by altering wrist posture influences the relationship between the time and frequency measures in both muscles. This suggests that in studies using EMG in different wrist postures, changes in the relationship between the time and the frequency measures should be considered.

EMG vs Precision and Accurancy in Dentistry

“…Roman-Liu and Bartuzi [18] analyses chosen sections of the EMG signal and divided them into parts. Out of them, they chose 3-second sections with the most stable value of the amplitude.…”

“…Before each measurement, the skin shall be properly prepared and its condition shall be checked so that between the electrode and the skin the resistance is not too large because it influences the result of the test. The skin is disinfected with an alcohol swab, shaved and disinfected one more time [18]. Another method of preparing the skin is wiping it with abrasive paper (in order to remove the outer layer of the epidermis) after prior shaving and then disinfecting it with alcohol [19].…”

“…Another method of preparing the skin is wiping it with abrasive paper (in order to remove the outer layer of the epidermis) after prior shaving and then disinfecting it with alcohol [19]. Electrodes should also be disinfected with alcohol and fixed to the skin surface with the use of a double-sided adhesive tape [18]. Gels or gel electrodes are the recommended method of decreasing the resistance.…”

Influence of type of MVC test on electromyography measures of biceps brachii and triceps brachii

“…However, others reported a decrease in muscle length resulting in a decrease in EMG amplitude [17]. Roman-Liu and Bartuzi [18] showed that a decrease in muscle length caused by altering the wrist posture influenced the relationship between the time and frequency measures in forearm muscles, whereas an increase in muscle length did not. Studies on BB [19,20] and TB [20] showed an increase in spectral parameters such as MF and MPF when the length of muscle decreased.…”

Flexor carpi radialis surface electromyography electrode placement for evoked and voluntary measures

“…The MPF we observed was 130 ± 33 H z at 100% MVC. Roman‐Liu and Bartuzi observed an MPF of 121 ± 28 H z while participants performed isometric contractions of the wrist flexors at 50% MVC. The higher MPF we observed was most likely due to muscle fiber conduction velocity changes between 50% and 100% MVC .…”