EMG signals were amplified using an ADInstruments bioAmp and the amplified signal was fed through a speaker so that the blindfolded subject could hear it. This was done with Ag–AgCl electrodes, attached to the skin with tape, with a solid gel contact point. To ensure that a subject's reference arm remained relaxed during the matches, surface EMG was monitored for biceps. The subject therefore did not need to generate any effort to maintain the position of the reference arm. In the second experiment, the experimenter placed the reference arm at a set angle where position of the arm was maintained by means of a support. He or she was then asked to match the angle with the other arm, that is, to align the two forearms by voluntarily moving the indicator arm. In the first experiment, the experimenter moved the reference forearm from the horizontal position, in the direction of flexion, to a predetermined angle and the subject, who was blindfolded, was asked to hold the arm in that position. Voltage signals were recorded by computer. Potentiometers attached to the paddle hinges provided an analog voltage signal proportional to joint angle. The angle of the upper arm was kept at approximately 45 deg to the horizontal. Each subject's forearms were strapped to two light-weight paddles, hinged at one end, with the hinges aligned with the subject's elbow joint. Measurements were carried out as described by Brockett et al. This increase in effort led to the matching errors.Ī preliminary report of this work was recently presented at a local scientific meeting ( Walsh et al. We concluded that the fall in force led to an increase in the effort required to maintain position of the limb against the force of gravity. The size of the errors correlated with the drop in force. The errors were in the direction reported by Saxton et al. In a forearm position matching task it was found that after a period of eccentric exercise which reduced muscle force by 40–50%, subjects made significant position matching errors. The findings led us to adopt a rather different point of view. The primary motivation for the experiments reported here was to try to reconcile the various observations. Several years ago we repeated those experiments under somewhat modified conditions and came up with a different result ( Brockett et al. (1995) found that eccentric exercise led subjects to make significant position matching errors in a forearm matching task. It has also been reported to produce a disturbance to proprioception Saxton et al. As a result it leaves them stiff and sore the next day ( Proske & Morgan, 2001). Eccentric exercise is interesting because it is the only form of mild exercise which routinely produces muscle damage if the individual is not trained to be protected against it ( Hough, 1902). We have been studying the effects of eccentric exercise on muscle properties. It was concluded that while a role for muscle spindles in kinaesthesia cannot be excluded, detailed information about static limb position can be derived from the effort required to support the limb against the force of gravity. That led to matching errors between the exercised and unexercised arms. The fall in force from fatigue after exercise meant more effort was required to maintain a given position. The data suggested that subjects were using as a position cue the perceived effort required to maintain a given forearm angle against the force of gravity. A similar pattern of errors was seen after concentric exercise, which does not produce muscle damage. Less consistent errors were observed when the reference arm was supported. Errors were in the opposite direction when the reference arm was exercised. Subjects matched the position of the unsupported reference arm, when this was unexercised, with a significantly more flexed position in their exercised indicator arm. After the exercise, subjects were asked to match the forearm angle of one arm, whose position was set by the experimenter, with their other arm. Damage indicators were a fall in force, change in resting elbow angle and delayed onset of soreness. After a period of eccentric exercise of elbow flexor muscles of one arm in young, adult human subjects, muscles became fatigued and damaged.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |