對於上肢功能完好的半身癱瘓者來說，使用手推式輪椅代步是普遍且經濟的選擇。輪椅使用者必須不斷地使用上肢來作為驅動手推式輪椅的動力來源，容易使其上肢的肌肉骨骼、關節及軟組織部分，增加額外的負荷。而當輪椅使用者以上肢取代下肢，作為承受重量及行動的功能時，便容易造成過度使用的疼痛或疲勞傷害。過去的研究指出，造成上肢疼痛的原因可能是肩關節不斷地承受高負荷。因此本篇便針對輪椅設計因子進行研究，目的在分析不同的手推輪框尺寸大小對肩關節肌肉的生物力學效應。

　　本研究根據1999年，黃等學者所發表的論文中所收集的12位健康受測者推動54 cm、43 cm、32 cm三種尺寸的手推輪輪椅時，上肢的運動學及動力學相關參數之實驗數據為基礎，再配合肩關節肌肉骨骼分析系統之計算，評估肩關節周圍的肌肉力量和關節拘束力等相關參數受到手推輪框尺寸的影響。最後利用單因子變異數分析（one-way ANOVA）來檢驗不同大小之手推輪框在肩關節肌肉收縮力量、收縮力量峰值發生時間參數上的差異。

　　實驗結果顯示，不同大小的手推輪框，對肩關節肌肉收縮力量、收縮力量峰值發生時間上有顯著地差異。隨著手推輪框的增大，肩關節的屈曲肌群、內收肌群、內旋肌群的肌肉收縮力量在推進期呈現上升的趨勢，且推進速度亦呈現上升的趨勢；因此，如何選擇最佳的適當的手推輪框尺寸，我們認為可以從增進推動效率及降低受傷風險，這兩個方向來考慮：若考慮效率上的需求，則建議使用者採用較大的手推輪框尺寸，可增加推進效率；若考慮降低受傷風險，則建議使用者採用較小的手推輪框尺寸，以減輕肩關節肌肉的負荷。

　　詳細的肌肉力量資料能幫助我們瞭解手推輪尺寸對肩關節複雜的機械功能及相關的生物力學效應。這些結果將有助於深入瞭解輪椅驅動過程中肩關節活動的情形與傷害發生的原因，深具臨床參考之意義。

　Manual wheelchairs are important to the functional independence of those who have disabilities, especially paraplegic spinal cord injury (SCI) patients. For the patients whose upper extremities are intact, it is a popular and economical choice to use manual wheelchairs as the substitution for their mobility. During wheelchair propulsion, users have to repeatedly move their upper extremities. Thus, injuries will easily occur on the muscle, skeletal, and soft tissues of upper extremities, and then increase additional loads. Therefore, overuse injuries and fatigue often happen on those who use their upper extremities for main functions. Among the manual wheelchair users, spinal cord injury (SCI) patients are one of major user groups, especially for those with lower paraplegia. Literatures demonstrate that one of the possible causes for this pain might be the high load on the shoulder during wheelchair propulsion.

　Based on Huang’s experimental data of the applied handrim force and movement trajectories of upper extremity during wheelchair propulsion, the computer graphics based shoulder model was used to analyze muscle forces of shoulder joint in order to understand the effect of the handrim size on recruited muscle contraction. Twelve ambulatory men were instructed to propel the wheelchair on the level ground. The diameter of the handrim used in the studies was 54 cm, 43 cm, and 32 cm, respectively. One-way ANOVA was used to analyze all parameters in relation to the handrim size and muscle force and muscle force peak time.

　The results show that handrim size has significant effects on muscle force and muscle force peak time. The bigger the handrim is, the larger the peak muscle forces of flexors, adductors and internal rotators and propelling velocity are. Therefore, how to choose an optimal handrim size may be considered from two points of view, to increase mechanical efficiency and to decrease injured risk. Increased handrim size increases the mechanical efficiency in propelling due to increased level arm around the wheel axle. However, it increases the muscle loading of the shoulder joint. Therefore, to decrease injured risk, it is suggested to choose the smaller handrim size.

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