Presentation is loading. Please wait.

Presentation is loading. Please wait.

 The Use of Surface Electromyography in Biomechanics by Carlo De Luca  JAB Vol 13, p 135-163; 1997  To its detriment, EMG is too easy to use and consequently.

Similar presentations


Presentation on theme: " The Use of Surface Electromyography in Biomechanics by Carlo De Luca  JAB Vol 13, p 135-163; 1997  To its detriment, EMG is too easy to use and consequently."— Presentation transcript:

1  The Use of Surface Electromyography in Biomechanics by Carlo De Luca  JAB Vol 13, p ; 1997  To its detriment, EMG is too easy to use and consequently too easy to abuse.  EMG provides easy access to physiological processes that cause the muscle to generate force and produce movement.  EMG has many limitations that must be understood, considered, and eventually removed so that the discipline is more scientifically based.

2  EMG signal/force Relationship Pitfalls  Is the EMG signal detected and recorded with maximum fidelity?  What are the configuration, dimension, and electrical characteristics of the electrode unit?  How Should the EMG signal be analyzed?  How are initiation and cessation times of EMG signal measured?  What are the preferred parameters for measuring the amplitude of the EMG signal?  What are the preferred parameters for measuring the frequency spectrum?  Where does the detected EMG signal originate?  Is there any crosstalk?  Where is the electrode placed on the surface of the muscle in relation to its anatomical structure?  How much fatty tissue is there between the electrode and the muscle surface?

3  EMG signal/force Relationship Pitfalls  Is the EMG signal sufficiently stationary for the intended analysis and interpretation?  Does the muscle change length?  Is the activation pattern of the motor units stable? That is, do some motor units alternate between the state of recruitment and derecruitment?  Where does the measured force originate?  What is the state of the synergistic and antagonistic muscles associated with the task?  Are the motor control characteristics of the contraction stable for the intended interpretation? Is there any change in the relative force contribution among muscles during the contraction?  Is the force generated homogenously throughout the muscle?

4  Electrode Structure and Placement Factors  Electrode configuration describes:  The area and shape of the electrode detection surfaces, which determine the number of active motor units detected by virtue of the number of muscle fibers in their vicinity, and  the distance between the electrode detection surfaces, which determines the bandwidth of the differential electrode configuration.  Location of the electrode with respect to the motor points in the muscle and the myotendinous junction, which influences the amplitude and frequency characteristics of the detected signal.  Location of the electrode on the muscle surface with respect to the lateral edge of the muscle, which determines the amount of crosstalk.  Orientation of the detection surfaces with respect to the muscle fibers, which affects the value of cond. vel., amplitude and frequency of signal.

5  Physiological, Anatomical, and Biochemical Factors  The number of motor units at any particular time of the contraction, which contributes to the amplitude of the detected signal.  Fiber type composition of the muscle, which determines the change in pH of the muscle during a contraction.  Blood flow in the muscle, which determines the rate at which metabolites are removed during the contraction.  Fiber diameter, which influences the amplitude and conduction velocity of the action potentials that constitute the signal.  Depth and location of the active fibers within the muscle with respect to the electrode detection surfaces; this relationship determines the spatial filtering, and consequently the amplitude and frequency characteristics of the detected signal.  The amount of tissue between the surface of the muscle and the electrode, which affects the spatial filtering of the signal.

6  Detection and Processing the EMG Signal  Differential Electrode Configuration:  Detection surfaces two parallel bars 1 cm apart  Bandwidth of Hz with a rolloff of 12 dB/octave  Common Mode Rejection Ratio > 80 dB  Noise < 2 uV RMS ( Hz)  Input Impedance > 100 MegaOhms  Locate the electrode on the midline of the muscle belly, between the myotendinous junction and the nearest innervation zone, with the electrodes aligned parallel to the muscle fibers.  Use RMS or average rectified EMG to measure the amplitude.

7  Comparisons Among Subjects, Muscles and Contractions  EMG/Force comparisons should be limited to isometric contractions with the joint constrained to limit the effects of other muscles  In dynamic movements use contractions that have the least amount of shortening and the slowest velocity and interpret the results with caution.  In repetitive dynamic contractions choose small sections of the motion to analyze.  When normalizing the amplitude of the EMG signal, do so at less than 80% MVC. Above this level, the EMG signal and force (torque) are exceptionally unstable and do not provide a suitable reference.  Measure MVC by choosing the greatest of three consecutive attempts.

8  Problems to be Resolved in EMG/Force Relations  Develop a surface detection that follows the movement of the muscle fibers.  Develop online EMG measurement  Develop a method to estimate muscle force with +- 5% from surface EMG.  How do muscle fibers transmit force throughout the muscle  Does a muscle generate force homogeneously throughout its volume.  Describe ansiotropy of muscle, fascia, fat and skin as related to EMG.  Refine anatomically correct biomechanical models of the musculoskeletal system.

9  Issues for International Agreement  Electrode configuration and dimensions.  Electrode placement and orientation.  Means for processing the EMG signal for amplitude and spectral analysis.  Means for determining the delay between force and the EMG signal.  Procedure for determining MVC  Procedures for establishing repeatability of the EMG:  among contractions when the experimental conditions are fixed  among contractions when the electrodes are reapplied  among muscles  among subjects


Download ppt " The Use of Surface Electromyography in Biomechanics by Carlo De Luca  JAB Vol 13, p 135-163; 1997  To its detriment, EMG is too easy to use and consequently."

Similar presentations


Ads by Google