許多健康相關行業常會因為使用徒手治療技巧治療病患而造成大拇指疼痛的問題，例如: 物理治療師使用後前向指尖施力的鬆動術技巧來治療病患。這樣的技巧需要作用於大拇指周圍的肌肉維持穩定度來協助力量傳遞到指尖。然而，目前為止，執行這樣徒手技巧時拇指的生物力學，則尚未被討論，故本研究想要透過人體實驗與建立模型來探討拇指在執行此類技巧時其各關節之生物力學，以提供治療師作為預防大拇指受傷之參考。此研究包含3個部分: (1)探討不同經驗的族群在執行3個後前向滑動鬆動術技巧時的運動學與動力學 (2)探討不同柔軟度的受試者，在執行後前向滑動鬆動術技巧與日常生活的捏取技巧時，生物力學上的差異 (3)以收集的資料建構一生物力學模型，來估計大拇指各個關節的受力，與大拇指周圍8條肌肉施力大小。
第一部分，收取23名無徒手經驗受試者，與15名有至少3年骨科徒手治療經驗的治療師，在6軸力板上執行3個後前向滑動鬆動術技巧，包括無支撐後前向滑動技巧(unsupported PA glide)，四指支撐之後前向滑動技巧(PA glide with digits supported)，以及食指支撐大拇指指間關節之後前向滑動技巧(PA glide with thumb interphalangeal joint supported by index finger)。利用表面肌電圖與動作分析系統，收取指尖施力大小、8條拇指肌肉的肌電活動，與拇指各關節運動學。經驗與執行技巧可影響大拇指內在肌肉活動與關節角度。有經驗的治療師會使用較少的內在肌肉活動，產生相同於無經驗者的力量，無經驗受試者則會依照技巧的本身的穩定度來增加內在肌肉的活動。有經驗治療師會傾向將腕掌關節擺在屈曲的位置下執行鬆動術技巧，而無經驗者則會擺在接近正中的位置下執行。建議柔軟度大的治療師執行較穩定(力量誤差小)的技巧(食指支撐大拇指指間關節之後前向滑動技巧)來將大拇指掌指關節擺在屈曲姿勢下防止傷害。
第二部分，33位健康受試者(柔軟度大組: 16位; 柔軟度小組:17位)，分別在六軸力板上，執行無支撐後前向滑動技巧、四指支撐之後前向滑動技巧 、側向捏取、指尖捏取等4個技巧，收取大拇指8條肌肉表面肌電圖、指間力量與大拇趾各關節動作。執行技巧對於指間產生力量與肌電圖有影響。不同的指間關節柔軟度族群對於指間產生力量、肌肉活動無顯著影響。柔軟度小的受試者傾向將指間關節與掌指關節擺位在接近正中(±5°)來執行2個鬆動術技巧。屈姆指短肌、屈姆指長肌和內收肌的肌肉活動，顯示這些肌肉在捏取技巧時是主要動作肌，然而，在執行鬆動術技巧時，這些肌肉會轉為提供維持大姆指穩定的角色。
第三部分，依據第一部分收集到的資料，建構一大姆指生物力學模型，來估算執行無支撐後前向滑動技巧、四指支撐之後前向滑動技巧時，大姆指各關節受力與8條肌肉力量。在執行鬆動術技巧時，有經驗治療師所有關節的關節接觸力都比無經驗者大，而2個族群的腕掌關節是關節接觸力受力最大的關節;而無經驗受試者相較於有經驗受試者，會產生較大的肌肉力量，特別是內在肌肉群(屈指短肌、伸指短肌、外展姆指短肌)。

Manual therapists frequently employ manual techniques such as posterior/anterior (PA) glide techniques to treatment patient with joint hypomobility disorders. Such tasks involve force generated at the tip of the thumb with the relevant muscles assuming the role of stabilizers for the multiarticular chain of the thumb. However, the exact roles of thumb muscles and kinematics while performing manual tasks are not clear. This part of the study had three objectives: (1) To investigate the effect of the experience and different techniques on kinematics and kinetics while performing three posteroanterior (PA) glide mobilization techniques. (2) To investigate the effect of the IP joint flexibility (hitchhiker’s thumb or not) and techniques (two PA glide mobilization and two pinch tasks) on thumb biomechanics. (3) To construct a biomechanical model to estimate forces acting on the joints and individual muscles of the thumb.
In part1 (chapter 2), 23 novice participants without any exposure to manual therapy and 15 physical therapists with at least 3 years of orthopedic experience participated. Each participant exerted maximum thumb-tip force on a 6-axis load cell with three different posterior-anterior (PA) glide techniques including unsupported PA glide (T1), PA glide with digits supported (T2) and PA glide with thumb interphalangeal (IP) joint supported by index finger (T3). Surface electromyographic activities of flexor pollicis brevis (FPB), adductor pollicis (ADP), abductor pollicis brevis (APB), and first dorsal interosseus (1stDI)) and kinematics of each thumb joint were collected for analyses. The magnitude of the thumb-tip force generated is influenced not only by the differences in technique employed by the therapists, but also by the general flexibility of the therapists. While participants of both groups generated the same magnitude of force, experienced participants generated less intrinsic muscle activity with a more flexed position at the CMC joint during PA glide mobilization. Novice participants increased activity of their intrinsic muscles in accordance with the stability status of the technique and performed with the CMC angles closer to the neutral position. Physical therapists with excessive thumb flexibility are advised to perform PA glide with IP joint supported (T3) which generated a greater tip force and was more stable among the three techniques employed in the present study. It produced the smallest relative errors in the thumb tip force generated and was executed in a more flexed position in the metacarpophalangeal (MCP) joints.
In part 2 (Chapter 3), 33 apparently healthy young participants (hitchhiker group: 8 males and 8 females; non-hitchhiker group: 8 males and 9 females) participated. Each participant exerted 1) thumb tip force on a 6-axis load cell from 25% to 100% maximum force at a 25% increments with two PA glide techniques (unsupported PA glide, T1, and PA glide with digits support, T2); and 2) tip pinch and lateral pinch tasks on a single axis load cell. Surface EMG of extensor pollicis longus (EPL), extensor pollicis brevis (EPB), flexor pollicis longus (FPL), flexor pollicis brevis (FPB), adductor pollicis (ADP), abductor pollicis longus (APL), abductor pollicis brevis (APB), and first dorsal interosseus (1stDI) were collected. Signficant main effects of technque on normalized thumb-tip force generated and on normalized EMG at all force levels except at 25% of maximum were shown. No obvious group (with or without hitchhiker’s thumb) difference (F=0.894, p=0.352) were revealed. While executing pinch tasks, FPL is required to help distal phalanx of the thumb to resist the forces exerted by the index. A greater ADP EMG activity was observed as it serves as a prime mover and is in a mechanically advantageous position. The EMG activity level of the FPB, FPL and ADP suggest that these muscles assume the roles of prime movers in pinch type of activities. However, their roles change to that of stabilizers during the performance of PA glide techniques. Non-hitchhikers seem to be more capable of maintaining the thumb in more neutral position.
In part 3 (Chapter 4), a biomechanical model was constructed to estimate joint constraint forces and individual muscle forces while performing unsupported PA glide (T1) and PA glide with digits support (T2). The mobilization technique results in a greater volar-ulnar directed force at the MCP joint and the largest contact forces were found at CMC joint in both groups. In both techniques, larger joint contact force in all three joints and smaller muscle forces (especially FPB, APB, EPB) were estimated in the Experienced Group than the Novice Group. This model, however, failed to estimate a muscle force pattern consistent with the activation pattern of the thumb muscles identified by surface EMG.

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