理想的輪椅靠背高度應取決於使用者本身軀幹的控制能力，及對於輪椅推動活動量的多寡而定；而太高的輪椅靠背可能會妨礙上肢的活動，進而減低其輪椅推動的效果。據此，本研究的目的在於驗證不同輪椅靠背的高度，在不同推進速度的情境下，是否對使用者上肢的活動度，及推進力學與推進效益產生影響。本研究方法採用重複施測的方式，共三十位下肢癱瘓之脊髓損傷輪椅使用者參與實驗。受測者分別使用不同高度的靠背，在輪椅運動平台上各自進行兩種速度(0.9 m/s、1.3 m/s)的推進活動，過程中分別記錄上肢的運動學與動力學資料。利用双因子重複量數變異數分析來驗證，以靠背高度及推進速度為主要影響因子，對於運動學與動力學資料等依變項的差異性。結果顯示，使用低於一半軀幹高的靠背時，因移除了靠背對上肢活動的限制，明顯可增加上肢向後伸展的角度(p = .03)，增進了上肢推動時的活動度(p < .01)，進而能有效的傳遞推進力量到輪圈上，避免無謂的施力浪費，提昇推進的機械效益(p = .02)，並有效的減少重覆性的推動頻率(p = .02)。在臨床應用上，針對具有軀幹控制能力，且經常性自主性推動輪椅的脊髓損傷患，可建議採用較低靠背的輪椅，來增進推動的效益，同時又避免因過高重覆性的輪椅推動，對上肢所誘發的續發性損傷。

An optimal backrest height depended on the wheelchair user's ability of trunk control and mobility. High backrests could impede the range of motion of upper arm,thereby reducing the propulsion efficiency.Therefore, the purpose of this study was to evaluate the effects of different backrest heights by examining the changes on the upper extremity kinematics and kinetics at different wheelchair propulsion speeds. A
repeated measurement design was used in this study. 30 manual wheelchair users with spinal cord injuries participated in this study. Participants were instructed to propel at two different speed conditions (0.9 m/s and 1.3 m/s) on a motor driven treadmill while using two different backrest heights respectively. Biomechanical data, such as kinematic and kinetic variables of the upper extremity, were collected during trials. A
two-way repeated measure analysis of variance (ANOVA) was used to examine the main effect of different heights and speeds on these kinematic and kinetic variables.The results showed that when pushing with the low backrest height, which was set at 50% of trunk height, participants could swing their upper arms more backward (p= .029) with large range of motion (p < .001), increase forces application on the pushrim, and avoid unnecessary force waste, thereby increasing propulsion efficiency(p = .015) with less propulsion cadence (p = .021). In clinical application, it was suggested that active manual wheelchair users who have sufficient trunk control should use the low backrest to improve propulsion performance. It also could prevent secondary injuries of upper extremities related to high frequency of repetitive propulsion movement.