Experiments were carried out to test the hypothesis that, in the absence of vision, position sense at the human forearm is generated by the combined input from muscle spindles in elbow flexor muscles and signals of central origin giving rise to a sense of effort. In a forearm position-matching task, to remove a possible contribution from the sense of effort, the reference arm was held supported at the test angle. Subjects were less accurate in matching elbow position of the supported forearm than when it was unsupported. Adding a 2 kg weight to the unsupported reference arm led subjects to make matching errors consistent with an increase in the effort signal. Evidence of a contribution from muscle spindles was provided by showing that the direction of position matching errors could be systematically altered by flexion or extension conditioning of the reference arm before its placement at the test angle. Such changes in errors with conditioning could be shown to be present when the reference arm was supported, unsupported, or unsupported and weighted. It is concluded that both peripheral signals from muscle spindles and signals of central origin, associated with the motor command required to maintain arm position against the force of gravity, can provide information about forearm position.

We recruited 25 patients after complete wrist denervation and 60 healthy adults to investigate conscious and unconscious proprioception of the wrist. Ipsi- and contralateral joint-position sense, force sense, and wrist reflexes were measured. The latter were triggered by a trapdoor, recording electromyographic signals from the extensor carpi radialis brevis, extensor carpi ulnaris, flexor carpi radialis, and flexor carpi ulnaris muscles. No significant differences were found for joint position sense, force sense, and wrist reflexes between both groups, except for reflex time of the flexor carpi ulnaris after denervation of the left wrist as compared with the left flexor carpi ulnaris in controls or in right operated wrists. At a mean follow-up of 32 months (range 8 to 133), we found no proprioceptive deficit of the conscious proprioceptive qualities of joint position sense, force sense, and the unconscious proprioceptive neuromuscular control of wrist reflex time for most muscles after complete wrist denervation. We conclude from this study that complete wrist denervation does not affect the proprioceptive senses of joint position, force sense, and reflex time of the wrist.

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