Simoneau Guy G, Marklin Richard W, Berman Joseph E
Department of Physical Therapy, Marquette University, Milwaukee, WI 53201-1881, USA.
Phys Ther. 2003 Sep;83(9):816-30.
Positioning a computer keyboard with a downward slope reduces wrist extension needed to use the keyboard and has been shown to decrease pressure in the carpal tunnel. However, whether a downward slope of the keyboard reduces electromyographic (EMG) activity of the forearm muscles, in particular the wrist extensors, is not known.
Sixteen experienced typists participated in this study and typed on a conventional keyboard that was placed on slopes at angles of 7.5, 0, -7.5, and -15 degrees. Electromyographic activity of the extensor carpi ulnaris (ECU), flexor carpi ulnaris (FCU), and flexor carpi radialis (FCR) muscles was measured with surface electrodes, while the extension and ulnar deviation angles of the right and left wrists were measured with electrogoniometers.
Wrist extension angle decreased from approximately 12 degrees of extension while typing on a keyboard with a 7.5-degree slope to 3 degrees of flexion with the keyboard at a slope of -15 degrees. Although the differences were in the range of 1% to 3% of maximum voluntary contraction (MVC), amplitude probability distribution function (APDF) of root-mean-square EMG data points from the ECU, FCU, and FCR muscles varied across keyboard slopes.
Wrist extension decreased as the keyboard slope decreased. Furthermore, a slight decrease in percentage of MVC of the ECU muscle was noted as the keyboard slope decreased. Based on biomechanical modeling and published work on carpal tunnel pressure, both of these findings appear to be positive with respect to comfort and fatigue, but the exact consequences of these findings on the reduction or prevention of injuries have yet to be determined. The results may aid physical therapists and ergonomists in their evaluations of computer keyboard workstations and in making recommendations for interventions with regard to keyboard slope angle.
将电脑键盘设置为向下倾斜的角度，可减少使用键盘时所需的手腕伸展幅度，并且已证实这样能降低腕管内的压力。然而，键盘向下倾斜是否能降低前臂肌肉，尤其是腕伸肌的肌电图（EMG）活动，目前尚不清楚。
16名经验丰富的打字员参与了本研究，他们在放置于7.5度、0度、 -7.5度和 -15度倾斜角度的传统键盘上打字。使用表面电极测量尺侧腕伸肌（ECU）、尺侧腕屈肌（FCU）和桡侧腕屈肌（FCR）的肌电图活动，同时使用电子测角仪测量左右手腕的伸展和尺偏角度。
在7.5度倾斜的键盘上打字时，手腕伸展角度约为12度，而在 -15度倾斜的键盘上打字时，手腕伸展角度变为3度的屈曲。尽管差异在最大自主收缩（MVC）的1%至3%范围内，但来自ECU、FCU和FCR肌肉的均方根肌电图数据点的幅度概率分布函数（APDF）会因键盘倾斜度的不同而变化。
随着键盘倾斜度降低，手腕伸展角度减小。此外，随着键盘倾斜度降低，ECU肌肉的MVC百分比略有下降。基于生物力学模型和已发表的关于腕管压力的研究，这两个发现对于舒适度和疲劳度而言似乎都是积极的，但这些发现对减少或预防损伤的确切影响尚未确定。这些结果可能有助于物理治疗师和人体工程学专家评估电脑键盘工作站，并就键盘倾斜角度提出干预建议。
