運動在近幾年來蔚為風行，無論是靜態養生運動或是動態激烈運動，都帶動了社會風氣以及相關產業。運動的好處良多，除了可以培養興趣，更可以鍛鍊體格和養生。
在運動過程中疲勞時產生的不穩定性，更加容易造成關節或肌肉的傷害。籃球選手在疲勞的時候可能會影響投籃的命中率;棒球選手在疲勞的時候可能會影響投球的穩定性，觀察疲勞後產生的不穩定性以及疲勞時關節的受力程度，為此研究的主要課題。
本實驗邀請了15名無上肢殘疾病史的年青男性參與實驗計畫，在正常速度下，進行屬於閉鎖式動力鏈運動的伏地挺身(Push-Up)運動及屬於開放式動力鏈運動的仰臥推舉(Bench-Press)運動。實驗使用三維動態分析系(Three-Dimensional Motion Analysis System,Motion Analysis Corp., Santa Rosa, C.A., U.S.A.），包括八部紅色可見光高速數位攝影機（Eagle and Hawk Digital Cameras）以及Kistler Instrument AG CH-8408 Winterthur / Schweiz公司所生產製造的壓電式測力板。
在這兩種運動實驗中，我們將分析伏地挺身以及仰臥推舉兩種運動在疲勞前(Initial)以及疲勞後(Fatigue)，其不穩定性角度的變化，以及關節活動角度、關節受力、關節力矩的變化。
實驗結果發現，伏地挺身運動在疲勞時，觀察兩肩的俯仰度(Pitching)以及偏搖度(Yawing)比起疲勞前有明顯的不穩定性產生，俯仰度有2.16°的角度變化、偏搖度有2.32°的角度變化。在伏地挺身運動疲勞時，觀察肘關節的角度變化，發現肘關節在身體下降時屈曲角度減少11.25°。並且在疲勞時肩關節在最大軸向壓力值增加18%；肘關節在最大側向剪力值增加10%、最大軸向壓力值減少4%、最大屈曲力矩值減少25%；腕關節在身體下降時軸向壓力增加12%。
而仰臥推舉在疲勞時，觀察槓鈴兩端的俯仰度以及偏搖度比起疲勞前有明顯的不穩定性產生，俯仰度有9.13°的角度變化、偏搖度有5.60°的角度變化。在仰臥推舉運動疲勞時，觀察肘關節的角度變化，發現肘關節在身體下降時屈曲角度減少5.9°。並且在疲勞時肩關節在最大前向剪力值減少4%；肘關節在前向剪力身體下降時減少42%、最大側向剪力值增加32%、最大軸向壓力值減少8%、最大外展力矩值減少27%、外旋力矩身體下降時減少25%；腕關節在最大側向剪力值增加55%。
整體而言，疲勞後上肢肘關節的剪力有明顯增加，而疲勞時的不穩定角度變化也相當明顯。疲勞時造成的上肢不穩定，亦提高了關節受傷的危險性。

The advantage of sports are a lot, except can foster interest, keep in body shape, keep in good health also. In exercise, the instability of extremity may cause the injury of the joint or the muscle when fatigue. The purpose of this study is to develop a biomechanical testing model to evaluate the effect of fatigue on joint loading and further investigate the relationship between fatigue and the degree of instability during kinetic-chain exercise of the upper extremity.
Fifteen healthy young male with no trauma history for this study. They were asked to complete open kinetic chain(Bench-Press) and closed kinetic chain(Push-Up) in normal speed. A Motion Analysis System (Three Dimensional Motion Analysis System,Motion Analysis Corp., Santa Rosa, C.A., U.S.A.In experiment), and one Force-Plate (Kistler Instrument AG CH-8408 Winterthur / Schweiz) were used to collect data.
We analysis the degree of instability, joint angle, joint force and joint moment when fatigue in two exercise.
In result, the Push-Up exercise shows the degree of instability (θ) increased 2.16° in pitching and increased 2.32° in yawing when fatigue. The degree of instability of initial and fatigue showed significant difference (P<0.05) in both of pitching and yawing. When fatigue, the elbow flexion angle in down was decreased 11.25°. And the Shoulder axial force peak was increased 18%. Elbow lateral force peak was increased 10%, axial compression peak was decreased 4%, flexion moment peak was decreased 25%. Wrist axial compression in down was increased 12%.
The Bench-Press exercise shows the degree of instability (θ) increased 9.13° in pitching and increased 5.60° in yawing when fatigue. The degree of instability of initial and fatigue showed significant difference (P<0.05) in both of pitching and yawing. When fatigue, the elbow flexion angle in down was decreased 5.9°. And the shoulder anterior force peak was decreased 4%. Elbow anterior force in down was decreased 42%, lateral force peak was increased 32%, axial compression peak was decreased 8%, extension moment peak was decreased 27%, external rotation in down was decreased 25%. Wrist lateral force peak was increased 55%.
In conclusion, when fatigue the elbow joint shear force are increase, and the upper extremity start rocked and become unstable, it may increase danger of joint injured.

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