ABSTRACT

　Quadriceps femoris （QF） muscle weakness is especially common after knee jointinjury and occurs due to both muscle atrophy and deficits in voluntary activation. Animportant cause of QF voluntary activation deficits is arthrogenic muscle inhibition（AMI）．In present study, neurological changes of the QF induced by prolongedvibration stimulation was used as a model of the AMI. This is because neurologicalchanges leaded by prolonged vibration stimulation were similar to that observed in theQF with the AMI. The purpose of present study is to investigate how the neurologicalabnormality would affect to reflex activities of thigh muscles during unexpectedlanding. The prolonged vibration stimulation significantly enhanced the averageEMG during time frame of the middle latency reflex （MLR） of the vastus lateralis （VL） and the biceps femoris （BF） only after the surprised landing even though noalternation of the MLR of the VL and the BF in both normal landings were found evenafter the application of prolonged vibration stimulation. These results suggested thatneurological alternations leaded by the prolonged vibration stimulation have no effecton landings accomplished by accurate feedforwarded information from brain basedon visual estimation. However, only when discrepancy was recognized between thefeedforward from brain and feedback from the proprioceptors in the lower limbs, theMLRs of the VL and BF were enhanced. the mechanism of the enhancement of theMLR via the attenuated afferents from proprioceptors to their brain might work as apreparatory mechanism in case startle events were imposed to them. In other words,in advance, a human brain might produce neurophysiological state in which the MLRcould easily be enhanced via disinhibited Ib interneurons as a compensatory strategy toprepare startle events.

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