200m程度の歩行で頻回に転倒するウェストファル現象が著明なパーキンソン病患者の転倒原因を探った。方法は, 症例に200m歩行させ, 歩行開始直後と歩行終了直前の右側前脛骨筋(TA), 腓腹筋の表面筋電図(EMG)と足関節角度を測定, 比較した。また, 歩行前後に同側のTAの最大等尺性収縮の50%(50%MVC)時のEMGを測定し, 歩行前後の筋電図積分値(iEMG), 平均パワー周波数(MPF)を比較した。結果, TAは1strideを通じて持続的に活動し腓腹筋の活動は乏しかった。足関節角度は歩行開始直後では常に背屈位であったが, 歩行終了直前では遊脚期で底屈傾向となった。また, 歩行前後のTAの50%MVC時のiEMGの比較では歩行後が有意に高値となり(P<0.05), MPFの比較では歩行後が有意に低値となった(P<0.01)。これらより本症例では, 背理性筋収縮に起因すると思われるTAの持続的な収縮が筋疲労を招き, 200m歩行程度で遊脚期の足関節背屈保持が困難となり転倒するものと考えられた。A study of the cause of frequent falling when walking about 200 meters in a patient who has a Westphal phenomenon resulting from Parkinson's disease is presented. Method : Surface electromyographical recordings (EMG) of the right tibialis anterior muscle (TA) and gastrocnemius muscle and ankle range of motion measurements were done just after beginning to walk and just before finishing walking 200 meters. In addition, 50% of the maximal isometric contraction (50%MVC) was determined through EMG recordings for the TA before and after walking ; integrated EMGs (iEMG) and mean power frequency (MPF) were compared. Results : The activity of the TA during one stride was continuous at a high level, and the gastrocnemius muscle contracted at a very low level. The position of the ankle joint was in dorsiflexion just after starting to walk, but, just before the end of gait, the foot was in plantar flexion during the swing phase. Also, for comparisons of 50%MVC of the TA, the iEMG showed a high advantage after the end of gait (p<0.05), and the MPF showed a low advantage (p<0.01). Therefore, we concluded that paradoxical contractions of the TA cause muscle fatigue, and, thus, cause this patient to be unable to dorsiflex the foot during the swing phase, resulting in his frequent falling.国立情報学研究所で電子
