Author： Schmit Brian D. Rymer W. Zev
Publisher： Springer Publishing Company
ISSN： 0090-6964
Source： Annals of Biomedical Engineering, Vol.29, Iss.4, 2001-04, pp. : 330-339
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Abstract
Static and dynamic components of the stretch reflex were studied in elbow flexors of 13 hemiparetic brain-injured individuals. Constant-velocity joint rotations were applied to the elbow, and the resulting stretch reflex torque and electromyographic responses were recorded in the biceps brachii and brachioradialis muscles. Ten elbow extension velocities between 6 and 150 \text{deg\ s}^{--1}</i> were applied in random order. The resulting reflex torque response was plotted as a function of elbow angle and fitted with a mathematical model designed to depict elbow flexor activation. We found that four of the six model parameters were essentially independent of test velocity. Conversely, 73% (19/26) of cases involving the other two model parameters were dependent on velocity of joint extension (p</i><0.05). we="" conclude="" from="" these="" results="" that="" four="" of="" the="" model="" parameters="" reflect="" the="" static="" reflex="" response="" while="" the="" two="" remaining="" velocity-dependent="" parameters="" reflect="" the="" dynamic="" reflex="" response.="" to="" describe="" overall="" velocity="" dependence="" of="" stretch="" reflexes="" in="" spastic="" elbow="" muscles,="" the="" two="" dynamic="" reflex="" parameters="" were="" fitted="" to="" a="" fractional="" exponential="" function="" of="" velocity,="" similar="" to="" a="" model="" previously="" used="" to="" describe="" spindle="" firing="" rate="" in="" the="" cat="" hindlimb.="" we="" found="" that="" the="" mean="" velocity="" exponent="" of="" the="" dynamic="" reflex="" parameters="" was="" 0.24="" +="" 0.17="" (s.d.)=""></0.05).>N</i> = 13), a value similar to that for muscle spindle velocity sensitivity in reduced animal preparations. We conclude that both static and dynamic reflex sensitivities can be measured by examining different aspects of the torque/angle relation associated with the reflex response to a large-amplitude ramp stretch of the elbow. © 2001 Biomedical Engineering Society.</i> PAC01: 8719St, 8719Ff, 8710+e
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