Muscle spindles play an important role in perception of head- neck position. The sensitivity of muscle spindles to stretch depends on how they have been conditioned beforehand. When a muscle is passively shortened, spindles are unable to take up the new shortened length and fall slack. This leaves them in a desensitised state. Our hypothesis is that neck muscles conditioned so that intramuscular receptors are in a desensitised state result in increased errors in head-neck position sense.

Two experiments on human subjects (n=7 and n=10) were conducted. Subjects were blindfolded, and their head-neck moved actively five times into flexion/extension. The head-neck was then moved passively to a pre-determined target head position. This process was repeated three times so that the subject familiarised themselves with the target position. The dorsal neck muscles were then conditioned to leave neck intramuscular receptors either tight (hold short conditioning) or slack (hold long conditioning). The end point of the conditioning procedure returned the head to a neutral position. From here the head-neck of the subject was passively moved toward the target head position and subjects were asked to identify when they reached that position.

There was a statistically significant difference between the hold long (12.5 +/- 1.8 deg) and hold short (10.5 +/- 0.8 deg) estimates of target position at 10 degrees. Similar results were obtained for other target positions. Conclusion: Neck muscle conditioning alters perception of head neck position in a predictable way. It is suggested that hold long conditioning decreases neck intramuscular afferent input to the CNS which disturbs head-neck kinaesthetic sensibility.

Grant Value: $20,186
Chief Investigator: Dr Barbara Polus – RMIT
Status: Completed

Researcher Updates:

This project was combined with a 2012 Grant, Muscle thixotrophy, subluxation and clumsiness.