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Physiological Measurements of Skeletal Muscle Activity

Physiological Measurements of Skeletal Muscle Activity. Electrical activity D in muscle length D in linear limb displacement D in linear whole body displacement D in joint angle Force Torque. Electrical Activity Measurement. Electromyography (EMG)

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Physiological Measurements of Skeletal Muscle Activity

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  1. Physiological Measurements of Skeletal Muscle Activity • Electrical activity • D in muscle length • D in linear limb displacement • D in linear whole body displacement • D in joint angle • Force • Torque

  2. Electrical Activity Measurement • Electromyography (EMG) • The most accurate means of determining the specific muscles used in a movement or activity • Direct (using needle electrodes) • Indirect (using surface transducers)

  3. pos v 0 neg v 1 sec Electromyography characteristics • Raw Signal Alternating current (AC) – Signal graphs as a series of changing positive and negative values Frequency is measured in Hertz (cycles per second) 1 Hz = 1 cycle per second Range of EMGs is 10-500Hz

  4. Fourier Transform • Fourier (mathematician) postulated that an irregular wave form consisted of the addition of a set of distinguishable waves • A Fourier Transform separates an irregular wave into its components • This process is sometimes called wave decomposition • Used in Electromyography to separate a combined set of signals into signals from separate sources

  5. Obtaining integrated EMG from raw EMG • Rectify signal • Take special average - root mean square (RMS) • Take area under trace of rectified signal per unit time.

  6. Full Wave Rectification Full wave rectification takes an AC signal and converts the negative values to positive. This allows the analysis of the absolute values of the signal.

  7. Full Wave Rectification

  8. RMS • Stands for Root Mean Square • The square root of the average of the squares of a set of numbers √(1/nSi=1...nX2i) EXAMPLE: Find the RMS of the following : 2, 3, 5 √( (22+32+52) /3) = √((38)/3 ) = 3.559

  9. RMS of Rectified Signal Peak values of rectified signal. The root mean square is taken of the set of peak values for the rectified voltage signal.

  10. Measurements Using EMG • Frequency profile of raw signal (frequency distribution) • Determines statistically how often a specific signal value occurs in a set of signals. • Amplitude of electrical signal (Integrated EMG) – Amplitude is the peak value of the signal.

  11. EMG Applications • Determining muscles or muscle groups to be targeted for training • Analyze neurological effects of activity • Therapy and Rehabilitation • electrical activity present after injury • biofeedback to analyze and train damaged or poorly functioning neuromuscular systems

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