Physiologic tremor is barely visible to the unaided eye unless it is enhanced by fatigue, anxiety, or a medication (e.g., thyroxin and beta-adrenergic drugs). Consequently, the study of physiologic tremor requires the use of sensitive motion transducers such as miniature accelerometers, gyroscopic angular velocity transducers, or force transducers. Muscle activity is recorded electromyographically, using skin electrodes for gross motor activity and needle electrodes for single motor unit activity (Elble and Deuschl 2002). Motion transducer and electromyographic (EMG) signals are usually recorded digitally with a computer and analyzed using spectral (Fourier) techniques to determine the amplitude and frequency of tremor and the coherence (linear correlation squared) between tremor and EMG activity. These electrophysiologic methods are also used to quantify the effect of mass (inertial) and spring (elastic) loading on tremor frequency. Using these methods, investigators have demonstrated mechanical-reflex and central-neurogenic mechanisms of physiologic tremor.
KeywordsPhysiologic tremor Accelerometry Electromyography Oscillation Stretch reflex Biomechanics
- Conway BA, Halliday DM, Farmer SF, Shahani U, Maas P, Weir AI, et al. Synchronization between motor cortex and spinal motoneuronal pool during the performance of a maintained motor task in man. J Physiol (Lond). 1995;489(3):917–24.Google Scholar
- Elble RJ, Deuschl G. Tremor. In: Brown WF, Bolton CF, Aminoff M, editors. Neuromuscular function and disease: basic, clinical and electrodiagnostic aspects. Philadelphia: W. B. Saunders; 2002. p. 1759–79.Google Scholar
- Lakie M, Walsh EG, Wright GW. Resonance at the wrist demonstrated by the use of a torque motor: an instrumental analysis of muscle tone in man. J Physiol (Lond). 1984;353:265–85.Google Scholar
- Stiles RN, Hahs DW. Muscle-load oscillations: detection, analysis and models. In: Wise DL, editor. Bioinstrumentation and biosensors. New York: Marcel Dekker; 1991. p. 75–119.Google Scholar
- Takanokura M, Sakamoto K. Neuromuscular control of physiological tremor during elastic load. Med Sci Monit. 2005;11(4):CR143–52.Google Scholar
- Wessberg J, Vallbo ÅB. Pulsatile motor output in human finger movements is not dependent on the stretch reflex. J Physiol (Lond). 1996;493(3):895–908.Google Scholar