Electromyography: Relationships & Applications

1. Electromyography: Relationships & Applications D. Gordon E. Robertson, PhD, FCSB Biomechanics Laboratory, School of Human Kinetics, University of Ottawa, Ottawa, Canada Biomechanics Laboratory, University of Ottawa

2. Isometric EMG • linear relationship for submaximal contractions • exponential relationship over full range • can be used as a control signal to regulate myoelectrically controlled devices Biomechanics Laboratory, University of Ottawa

3. Isometric EMG • exponential over full range especially when normalized to maximum force Biomechanics Laboratory, University of Ottawa

4. Force-velocity • Hill’s equation illustrates that as speed of muscle shortening increases, force decreases • but for eccentric contractions force increases with speed of lengthening Biomechanics Laboratory, University of Ottawa

5. Force-velocity-length • force varies with both length and velocity of contraction • also pre-history, i.e., prestreched, fatigued, or relaxed Biomechanics Laboratory, University of Ottawa

6. experiment by Komi measured EMG of three muscles measured maximum force at different speeds of contraction Maximum EMG Biomechanics Laboratory, University of Ottawa

7. Maximum EMG • results of force similar to Hill’s equation and Gordon & Huxley Biomechanics Laboratory, University of Ottawa

8. Maximum EMG • EMGs did not vary across velocity of contraction Biomechanics Laboratory, University of Ottawa

9. EMG during Dynamic Contractions strong correlation between level of concentric contraction and EMG weak correlation between level of eccentric contraction and EMG EMG level is often greater during a brief rapid MVC then during a sustained MVC following figures show biceps and triceps brachii during a horizontal rapid flexion extension movement, an electrogoniometer was used to monitor elbow angle Biomechanics Laboratory, University of Ottawa

10. Biceps Triceps Angle Velocity Accel. Concentric flexion Concentric extension Flexing Extending Concentric flexion by biceps Concentric extension by triceps Flexion Extension Biomechanics Laboratory, University of Ottawa

11. Biceps Triceps Angle Velocity Accel. Low EMG to stop extension Stopping extension with biceps Stopping flexion with triceps Flexion Extension Biomechanics Laboratory, University of Ottawa

12. Biceps Triceps Angle Velocity Accel. In this trial flexion was stopped by ligaments and bones Flexion Extension Flexing Extending Biomechanics Laboratory, University of Ottawa