The tricepes muscle in the back of the upper arm is an extensor. When it contracts, the elbow strainghtens and the forearm and hand move away from the shoulder.
而后上臂的肱三头肌则是一块伸肌，当它运动时，肘部就伸直，而前臂和手就离开了肩部。
The tricepes muscle in the back of the upper arm is an extensor. When it contracts, the elbow strainghtens and the forearm and hand move away from the shoulder.
而后上臂的肱三头肌则是一块伸肌，当它运动时，肘部就伸直，而前臂和手就离开了肩部。
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