Oxygenation And Myoelectric Activity In The Forearm And Shoulder Muscles Of Males And Females

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Linear relationships exist as decreasing oxygenation (StO2%) and increasing myoelectric activity (EMG) for the biceps brachii and brachioradialis muscles. This relationship is not yet established for the trapezius and extensor carpi radialis (ECR) muscles, i.e. muscles prone to work-related pain (WRMP). In regard, females have a higher incidence of WRMP. PURPOSE: To determine the relations between StO2% and EMG in the trapezius and ECR muscles of males and females during isometric contractions (10-70 % MVC). METHODS: Thirteen males and fifteen females (26 ± 5 yrs for both) were equipped with probes for near infrared spectroscopy (NIRS) and EMG over the right forearm ECR and shoulder trapezius muscles. For the ECR measurements wrist extensions, and for the trapezius elevation of the shoulder joints were performed. From NIRS data the change in StO2% from baseline (DStO2%) was calculated. EMG amplitudes (RMS, root mean square) were expressed as percentages of maximum. Slope values (k) between DStO2% and EMG RMS and correlation coefficients (R) were calculated for each subject and mean differences tested with T-tests. RESULTS: For the ECR, the mean slope for females (k=-0.67) tended to be steeper than males (k=-0.48), (p=0.10). Females also tended to correlate better (R=-0.87) than males (R=-0.60), (p=0.06). For the trapezius, slopes and correlations for males (k=-0.60, R=-0.71) and females (k=-0.56, R=-0.77) were not different. Mean (± SE) DStO2% and EMG-RMS over force are shown below. CONCLUSION: Our results show a gender specific pattern for the relation between StO2% and EMG for the ECR, but not for the trapezius. Whether this has an impact on the higher incidence of WRMP for females than males requires further investigation.FIGURE