Received September 17, 2007
Revised October 22, 2007
Accepted after revision November 19, 2007
Human, Environmental & Exercise [250]
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Evidence from proprioception of fusimotor co-activation during voluntary contractions
Trevor J Allen 1,
Gabrielle E Ansems 1,
Uwe Proske 1*
1 Monash University
* To whom correspondence should be addressed. E-mail: uwe.proske{at}med.monash.edu.au.
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Abstract |
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In experiments on position sense at the elbow joint in the horizontal plane, blindfolded subjects were required to match the position of one forearm (reference) by placement of their other arm (indicator). Position errors were measured after conditioning elbow muscles of the reference arm with an isometric contraction while the arm was held either flexed or extended. The difference in errors after the two forms of conditioning was large when the conditioned muscles remained relaxed during the matching process and it became less when elbow muscles were required to lift a load during the match (10% and 25% of maximum voluntary contraction). Errors from muscle conditioning were attributed to signals arising in muscle spindles and were hypothesized to result from the thixotropic property of passive intrafusal fibres. Active muscle does not exhibit thixotropy. It is proposed that during a voluntary contraction the errors after conditioning are less, because the spindles become co-activated through the fusimotor system. The distribution of errors is therefore seen to be a reflection of fusimotor recruitment thresholds. For elbow flexors most, but not all, fusimotor fibres appear to be recruited by 10% of maximum of the contraction.
Key Words:
Mechanoreceptor, Muscle contraction, Proprioception
