The Surface Mechanomyogram (MMG)

1. 1.82Volts 0 1 2 3 seconds 3.44 ms-2 55 Nm 406 μV The Surface Mechanomyogram (MMG)

2. Mechanomyography (MMG) • Non-invasive technique that records and quantifies the oscillations generated by dimensional changes of the active skeletal muscle fibers. • Has also been called acoustic myography, phonomyography, sound myography, and vibromyography. • “surface mechanomyogram” recommended at CIBA Foundation Symposium, 1995.

3. Orizio, C. Critical Reviews in Biomedical Engineering. 1993. force sound water line muscle hydrophone • When muscle fibers contract they oscillate or vibrate. • Early MMG studies utilized isolated frog muscle in a sound-insulated chamber and recorded the oscillations with a hydrophone.

4. Displacement Sensor Accelerometer Laser Beam Bipolar EMG Electrodes Force Transducer Orizio, C., Gobbo, M., Diemont, B., Esposito, F., Veicsteinas, A. Eur J Appl Physiol. 2003. Isometric muscle action at 30% MVC

5. Watakabe, M., Itoh, Y., Mita, K., and Akataki, K. Med. Biol. Eng. Comput. 1998. • During voluntary contractions, the oscillations create pressure waves that can be recorded at the skin’s surface using a crystal contact sensor or accelerometer.

6. Over the years, there have been a number of hypotheses regarding the origin of the MMG signal that have been ruled out. • Vascular sounds • MMG can be recorded when blood flow is occluded. • Friction between the microphone and skin • MMG can be recorded in a water bath and with air coupled microphones. • Friction between fascia and muscles • Less MMG activity is recorded over fascia such as the vastus lateralis. • No MMG activity during passive muscle actions. • Bone oscillations • MMG can be recorded from isolated muscle. • Nerve conduction • Ambient temperature does not affect MMG frequency, but does affect nerve conduction velocity.

7. The MMG signal has three components: • A gross lateral movement at the initiation of a contraction generated by a non-simultaneous activation of muscle fibers. • Smaller subsequent lateral oscillations at the resonant frequency of the muscle. • Dimensional changes of the active fibers. Smith, D.B., Housh, T.J., Johnson, G.O., Evetovich, T.K., Ebersole, K.T., Perry, S.R. Muscle Nerve. 1998.

8. The MMG signal is affected by many factors: • Muscle temperature • Stiffness • Mass • Intramuscular pressure • Viscosity of the intracellular and extracellular fluid mediums

9. Perry, S.R., Housh, T.J., Weir, J.P., Johnson, G.O., Bull, A.J., Ebersole, K.T. J. Electromyogr. Kinesiol. 2001. • The MMG signal is low frequency: • Typically bandpass filtered at 5-100 Hz, while EMG is 10-500 Hz.

10. Time and frequency domains of the MMG signals have been used to examine various aspects of muscle function including: • Neuromuscular fatigue • Electromechanical delay • Motor control strategies • Muscle fiber type distribution patterns • Diagnose neuromuscular disorders in adult and pediatric populations • Low back pain • Control external prostheses • Effectiveness of anesthesia

11. Although we are continually learning more, our knowledge of the MMG signal is probably 20-25 years behind that of the EMG signal. • M. Stokes: • “As knowledge of muscle sounds increases and the development of more appropriate methodology occurs, the potential uses and limitations of [MMG] must be reassessed continually.”

12. We have examined the MMG signal in the time and frequency domains under a number of conditions in an attempt to both develop and test hypotheses. • Isometric muscle actions • Concentric muscle actions • Eccentric muscle actions • Passive movements • Cross-talk • Stretching interventions • Resistance training interventions

13. Isometric and Isokinetic Force vs. MMG and EMG amplitude and frequency relationships

14. Coburn, J.W., Housh, T.J., Cramer, J.T., Weir, J.P., Miller, J.M., Beck, T.W., Malek, M.H., and G.O. Johnson. Electromyogr clin Neurophysiol. 2004. Torque increase is due to increased motor unit firing rate and not recruitment at > 80% MVC since MMG amplitude decreases. Increase in torque due only to increased recruitment of ST fibers – no change in frequency Increased frequency due to recruitment of FT fibers at > 50% MVC; these fibers have greater frequency than ST fibers • Subjects: • n = 10 (7 male, 3 female). • Muscle actions: • Leg extension: • Isometric = 45° • Isokinetic = 30°∙s-1 • Torque: • 10 – 100% MVC. • Parameters: • MMG amplitude and frequency. • Muscles: • Vastus medialis. 1.0 .9 .8 .7 .6 Normalized MMG rms and MPF .5 .4 .3 .2 .1 0.0 0 10 20 30 40 50 60 70 80 90 100 Percent Maximal Torque

15. Coburn, J.W., Housh, T.J., Cramer, J.T., Weir, J.P., Miller, J.M., Beck, T.W., Malek, M.H., & Johnson, G.O. (2004). J Strength Cond Res. in press. • Subjects: • n = 7 men • Muscle actions: • Leg extension: • Isometric = 45° • Isokinetic = 30°∙s-1 • Torque: • 20 – 100% MVC. • Parameters: • MMG & EMG amplitude and frequency. • Muscles: • Vastus medialis.

16. Coburn, J.W., Housh, T.J., Cramer, J.T., Weir, J.P., Miller, J.M., Beck, T.W., Malek, M.H., & Johnson, G.O. (2004). J Strength Cond Res. in press. • Subjects: • n = 7 men • Muscle actions: • Leg extension: • Isometric = 45° • Isokinetic = 30°∙s-1 • Torque: • 20 – 100% MVC. • Parameters: • MMG & EMG amplitude and frequency. • Muscles: • Vastus medialis. Vastus Medialis

17. Orizio, C., Gobbo, M., Diemont, B., Esposito, F., A. Veicsteinas. Eur J Appl Physiol. 2003. Biceps Brachii

18. Assignments • Complete all the normalization and graphing for our experimental data. • Randomly assign the 5 articles posted on the website tonight • Give a presentation on your article next week. • PPT, 10 min, 5-min Q & A • Discuss the results of your article and how they relate to our study. • Mid-term exam/lab write-up (take home) due Monday after spring break (March 21).