Human motor control consequences of thixotropic changes in muscular short-range stiffness
2001 (English)In: Journal of Physiology, ISSN 0022-3751, E-ISSN 1469-7793, Vol. 535, no Pt 1, 279-288 p.Article in journal (Refereed) Published
- The primary aim of the present study was to explore whether in healthy subjects the muscle contractions required for unrestrained voluntary wrist dorsiflexions are adjusted in strength to thixotropy-dependent variations in the short-range stiffness encountered in measurements of passive torque resistance to imposed wrist dorsiflexions.
- After a period of rest, only the first movement in a series of passive wrist dorsiflexions of moderate amplitude exhibited clear signs of short-range stiffness in the torque response. During analogous types of voluntary movements, the extensor EMG during the first movement after rest showed a steep initial rise of activity, which apparently served to compensate for the short-range stiffness.
- The passive torque resistance to minute repetitive wrist dorsiflexions (within the range of short-range stiffness) was markedly reduced after various types of mechanical agitation. During analogous low-amplitude voluntary wrist dorsiflexions the extensor EMG signals were weaker after than before agitation.
- Mechanical agitation also led to enhancement of passive dorsiflexion movements induced by weak constant torque pulses. In an analogous way, the movement-generating capacity of weak voluntary extensor activations (as determined by EMG recordings) was greatly enhanced by mechanical agitation.
- The signals from a force transducer probe pressed against the wrist flexor tendons - during passive wrist dorsiflexions - revealed short-range stiffness responses which highly resembled those observed in the torque measurements, suggesting that the latter to a large extent emanated from the stretched, relaxed flexor muscles. During repetitive stereotyped voluntary wrist dorsiflexions, a close correspondence was observed between the degree of short-range stiffness as sensed by the wrist flexor tension transducer and the strength of the initial extensor activation required for movement generation.
- The results provide evidence that the central nervous system in its control of voluntary movements takes account of and compensates for the history-dependent degree of inherent short-range stiffness of the muscles antagonistic to the prime movers.
Place, publisher, year, edition, pages
2001. Vol. 535, no Pt 1, 279-288 p.
IdentifiersURN: urn:nbn:se:uu:diva-224123DOI: 10.1111/j.1469-7793.2001.00279.xPubMedID: 11507177OAI: oai:DiVA.org:uu-224123DiVA: diva2:715343