Finucane S D, Mayhew T P, Rothstein J M
Department of Physical Therapy, Medical College of Virginia, Virginia Commonwealth University, Richmond 23298-0224.
Phys Ther. 1994 Dec;74(12):1125-33. doi: 10.1093/ptj/74.12.1125.
Torques reflecting muscle performance must be corrected for the effects of gravity if error-free ratio-scaled data are to be obtained. Ratio-scaled data are necessary, for example, to report muscle performance characteristics in terms of ratios or percentages or in the form of ratios with another muscle (eg, ratio of hamstring to quadriceps femoris muscle peak torque). The purpose of this study was to determine the error associated with the gravity-correction procedure of the Kin-Com dynamometer when a weight or limb segment is weighed at different lever arm positions.
A known weight was suspended from the lever arm of the Kin-Com dynamometer. The rotational component of gravitational forces on the weight was measured at 11 different angular positions. We compared the force measurement obtained from the Kin-Com with the predicted rotational component at each angular position. The gravitational forces on a subject's limb segment (leg) were then measured at 12 different angular positions in each of two trunk positions (sitting and supine). We compared the force measurement obtained from the Kin-Com with the predicted rotational component for each position. Forces measured for the two trunk positions with the lever arm horizontal were compared. Forces measured with the knee extended were compared with forces measured with the lever arm horizontal.
The dynamometer accurately recorded the rotational component of gravitational forces for the weight suspended from the lever arm. There was a progressively greater discrepancy between measured forces and predicted forces for the leg as the lever arm was moved from horizontal to 50 degrees below the horizontal. The force recorded with the Kin-Com was greater when the subject's knee was in full extension than when the lever arm was horizontal, which placed the subject's knee in a flexed position. A small difference was noted between the measured forces with the lever arm horizontal when the subject was sitting compared with when the subject was positioned supine.
When weighing a leg with this dynamometer, we recommend that the lever arm be as close to the horizontal position as possible. Positions of proximal joints should be chosen that do not put two joint muscles in stretched positions.
如果要获得无误差的比率缩放数据，则必须针对重力影响对反映肌肉性能的扭矩进行校正。例如，比率缩放数据对于以比率或百分比形式报告肌肉性能特征或以与另一肌肉的比率形式（例如，绳肌与股四头肌峰值扭矩之比）是必要的。本研究的目的是确定当重量或肢体节段在不同杠杆臂位置称重时，与Kin-Com测力计重力校正程序相关的误差。
将一个已知重量悬挂在Kin-Com测力计的杠杆臂上。在11个不同角度位置测量重量上重力的旋转分量。我们将从Kin-Com获得的力测量值与每个角度位置的预测旋转分量进行比较。然后在两个躯干位置（坐姿和仰卧位）的每一个中，在12个不同角度位置测量受试者肢体节段（腿部）上的重力。我们将从Kin-Com获得的力测量值与每个位置的预测旋转分量进行比较。比较杠杆臂水平时两个躯干位置测量的力。比较膝关节伸展时测量的力与杠杆臂水平时测量的力。
测力计准确记录了悬挂在杠杆臂上的重量的重力旋转分量。随着杠杆臂从水平位置移动到水平以下50度，腿部测量力与预测力之间的差异逐渐增大。当受试者的膝关节完全伸展时，Kin-Com记录的力大于杠杆臂水平时的力，此时受试者的膝关节处于屈曲位置。当受试者坐姿与仰卧位时，杠杆臂水平时测量的力之间存在微小差异。
使用该测力计称量腿部时，我们建议杠杆臂尽可能接近水平位置。应选择近端关节的位置，使双关节肌肉不处于伸展位置。
