肌腱在人體動作功能中扮演重要的角色，其為肌肉與骨骼間的連結橋樑，主要功能為傳遞肌肉力量到所連接的骨頭上，進而帶動身體肢段產生動作。然而肌腱病變為臨床常見的骨骼肌肉系統疾病，特別是好發於上肢的網球肘，病患主要症狀為肱骨外側上髁處的壓痛與執行腕關節或手指伸展動作時會伴隨疼痛，其致病機轉可能為伸腕或伸指肌群過度使用導致的累積性小創傷，或者急速且過度用力對肌腱造成太大的負荷。
為探討肘關節肌腱損傷之受傷機轉，本研究以肌肉疲勞模擬伸腕肌群過度使用情形，藉由本團隊自行開發之腕關節等速肌力評估系統，控制肌肉收縮形態與腕關節偏移角度，以了解正常人於肌肉疲勞後，在不同腕關節姿勢(自然角度/尺側偏移/橈側偏移)與不同收縮形態(等長/等速向心/等速離心)下，對肌肉力量及肌電訊號變化之影響。此外，本研究亦利用超音波影像探討健康受試者於伸腕肌群肌肉疲勞後，在不同腕關節姿勢下之總伸肌腱受力與肌腱變形量情形，藉此了解健康人與肌肉疲勞之肌腱的生物力學特性。
結果顯示於肌肉疲勞後，伸腕肌群最大力量、肌電訊號之均方根值與肌腱之勁度(stiffness)都有顯著下降。此外，離心收縮與向心收縮之力量比值，在疲勞後也有下降之趨勢。而在不同腕關節姿勢下，自然角度下之肌力會顯著大於橈側偏移與尺側偏移角度；然而，當腕關節角度偏移時，不論是在離心或向心收縮下，其肌肉活化程度相較於自然位置也有顯著下降。對於肌腱之機械特性的探討，腕關節於自然位置之肌腱勁度也顯著大於橈側偏移與尺側偏移角度。表示當伸腕肌群過度使用或肌肉疲勞時，亦或是腕關節處於不適當角度施力，不僅會影響伸腕肌群力量的產生，還會改變肌腱的勁度導致更大的變形量去傳遞相同的力量，尤其是使用橈側偏移角度或離心收縮下施力，上述之現象可能是造成肌腱病變之致病因子。
此研究運用力學設計、影像技術及臨床等研究方法，探討肌腱肌肉疲勞機制與造成肌腱損傷之因素。未來可進一步探討肌腱之受傷機制並建立一個科學量化的參考，以提供更多客觀證據協助臨床診斷之工作，進而改良現有治療技術或開發新的復健策略。

Tendons play an important role in human movements because it connects muscle and bone. The main function is to transfer the force produced by the muscle to move and stabilize joints. However, tendinopathy is a common musculoskeletal disorder, especially tennis elbow (lateral epicondylitis) which is the most common one upper extremity tendinopathy disorder. Patients with tennis elbow experience pain associated with wrist movements or tenderness over the lateral epicondyle of the humerus. The possible injury mechanism for this disease might be sudden impact of overload on the involved muscle/tendon or cumulative microtrauma from repetitive loading on the wrist extensors.
In order to understand the disease factor of tennis elbow, this study used a muscle fatigue model to simulate overuse of the wrist extensor muscle via a custom isokinetic dynamometer of the wrist joint and provided the functions to control muscle contraction mode and wrist deviation angle. The aim of this study is to investigate the performance of muscle strength, muscle activity in healthy subjects during different wrist deviations (neutral/ radial deviation/ ulnar deviation) and muscle contraction types (isometric/ concentric/ eccentric) after wrist extensor fatigue. Also, this study will help to understand the biomechanical behavior of common extensor tendon such as tendon stiffness between healthy subjects and muscle fatigue.
The results showed that, after the muscle fatigue, the strength of wrist extensors, the root mean square of muscle activity and tendon stiffness were reduced. The wrist extensor muscle strength in neutral wrist position was significantly greater than radial and ulnar deviation of wrist joint. In addition, whether in different contraction types, the muscle activity was significantly decreased in comparison with wrist neutral position. The tendon stiffness also significantly decreased in wrist deviations. Based on the above mentioned, the condition of wrist extensor muscle fatigue or overuse and during the movements in wrist deviations, which not only decrease muscle strength but also decrease of tendon stiffness, it result in tendon has more displacement to transfer the same tendon force. The findings indicate that the possible injury may result from the fatigue or overuse, especially in eccentric movements or in radial deviation of wrist joint.
In conclusion, this study applies the mechanical design, imaging technology and clinical setting to investigate the fatigue mechanism of muscle/tendon and the factors of tendon injury or muscle damage. In the future, further studies can find the injury mechanisms of tendons and establish more objective evidences to give assistance in clinical diagnosis to improve therapy, or develop a functional outcome measurement and apply it to evaluate effectiveness of interventions.

Alizadehkhaiyat, O., Fisher, A. C., Kemp, G. J., & Frostick, S. P. (2007). Strength and fatigability of selected muscles in upper limb: assessing muscle imbalance relevant to tennis elbow. Journal of Electromyography and Kinesiology, 17(4), 428-436. doi: 10.1016/j.jelekin.2006.04.007
Allen, D. (2001). Eccentric muscle damage: mechanisms of early reduction of force. Acta Physiologica Scandinavica, 171(3), 311-319.
Allen, D. G., Lamb, G., & Westerblad, H. (2008). Skeletal muscle fatigue: cellular mechanisms. Physiological Reviews, 88(1), 287-332.
Arya, S., & Kulig, K. (2010). Tendinopathy alters mechanical and material properties of the Achilles tendon. J Appl Physiol (1985), 108(3), 670-675. doi: 10.1152/japplphysiol.00259.2009
Bernardi, M., Felici, F., Marchetti, M., Montellanico, F., Piacentini, M., & Solomonow, M. (1999). Force generation performance and motor unit recruitment strategy in muscles of contralateral limbs. Journal of Electromyography and Kinesiology, 9(2), 121-130.
Bilodeau, M. (2006). Central fatigue in continuous and intermittent contractions of triceps brachii. Muscle and Nerve, 34(2), 205-213.
Burgess, K. E., Graham-Smith, P., & Pearson, S. J. (2009). Effect of acute tensile loading on gender-specific tendon structural and mechanical properties. Journal of Orthopaedic Research, 27(4), 510-516. doi: 10.1002/jor.20768
Campbell, J. C. (2007). Effects of Concentric and Eccentric Contractions of the Knee Extensors on Mechanical Work, Lactate Concentration, and Surface EMG: ProQuest.
Cifrek, M., Medved, V., Tonković, S., & Ostojić, S. (2009). Surface EMG based muscle fatigue evaluation in biomechanics. Clinical Biomechanics, 24(4), 327-340. doi: http://dx.doi.org/10.1016/j.clinbiomech.2009.01.010
Delp, S. L., Grierson, A. E., & Buchanan, T. S. (1996). Maximumisometric moments generated by the wrist muscles in flexion-extension and radial-ulnar deviation. Journal of Biomechanics, 29(10), 1371-1375.
Desbrosses, K., Babault, N., Scaglioni, G., Meyer, J.-P., & Pousson, M. (2006). Neural activation after maximal isometric contractions at different muscle lengths. Medicine and Science in Sports and Exercise, 38(5), 937-944.
Dimitrov, G. V., Arabadzhiev, T. I., Mileva, K. N., Bowtell, J. L., Crichton, N., & Dimitrova, N. A. (2006). Muscle fatigue during dynamic contractions assessed by new spectral indices. Medicine and Science in Sports and Exercise, 38(11), 1971-1979. doi: 10.1249/01.mss.0000233794.31659.6d
Ellenbecker, T. S., Roetert, E. P., & Riewald, S. (2006). Isokinetic profile of wrist and forearm strength in elite female junior tennis players. British Journal of Sports Medicine, 40(5), 411-414. doi: 10.1136/bjsm.2005.023358
Enoka, R. M. (1996). Eccentric contractions require unique activation strategies by the nervous system. Journal of Applied Physiology, 81(6), 2339-2346.
Fan, Z. J., Silverstein, B. A., Bao, S., Bonauto, D. K., Howard, N. L., Spielholz, P. O., . . . Viikari‐Juntura, E. (2009). Quantitative exposure‐response relations between physical workload and prevalence of lateral epicondylitis in a working population. American Journal of Industrial Medicine, 52(6), 479-490.
Finni, T. (2001). Muscle mechanics during human movement revealed by in vivo measurements of tendon force and muscle length: Jyväskylän yliopisto.
Finsen, L., Sogaard, K., Graven-Nielsen, T., & Christensen, H. (2005). Activity patterns of wrist extensor muscles during wrist extensions and deviations. Muscle and Nerve, 31(2), 242-251. doi: 10.1002/mus.20237
Gandevia, S. (1998). Neural control in human muscle fatigue: changes in muscle afferents, moto neurones and moto cortical drive. Acta Physiologica Scandinavica, 162(3), 275-283.
Gerdle, B., Larsson, B., & Karlsson, S. (2000). Criterion validation of surface EMG variables as fatigue indicators using peak torque: a study of repetitive maximum isokinetic knee extensions. Journal of Electromyography and Kinesiology, 10(4), 225-232.
Gonzalez-Izal, M., Cadore, E. L., & Izquierdo, M. (2013). Muscle conduction velocity, surface electromyography variables, and echo intensity during concentric and eccentric fatigue. Muscle and Nerve, n/a-n/a. doi: 10.1002/mus.23926
Gonzalez, R. V., Buchanan, T. S., & Delp, S. L. (1997). How muscle architecture and moment arms affect wrist flexion-extension moments. Journal of Biomechanics, 30(7), 705-712. doi: http://dx.doi.org/10.1016/S0021-9290(97)00015-8
Grabiner, M. D., & Owings, T. M. (2002). EMG differences between concentric and eccentric maximum voluntary contractions are evident prior to movement onset. Experimental Brain Research, 145(4), 505-511. doi: 10.1007/s00221-002-1129-2
Hägg, G. M., Öster, J., & Byström, S. (1997). Forearm muscular load and wrist angle among automobile assembly line workers in relation to symptoms. Applied Ergonomics, 28(1), 41-47. doi: http://dx.doi.org/10.1016/S0003-6870(96)00033-6
Hashemi, J., Chandrashekar, N., & Slauterbeck, J. (2005). The mechanical properties of the human patellar tendon are correlated to its mass density and are independent of sex. Clinical Biomechanics, 20(6), 645-652. doi: http://dx.doi.org/10.1016/j.clinbiomech.2005.02.008
Huang, C. T., Hwang, I. S., Huang, C. C., & Young, M. S. (2006). Exertion dependent alternations in force fluctuation and limb acceleration during sustained fatiguing contraction. European Journal of Applied Physiology, 97(3), 362-371. doi: 10.1007/s00421-006-0166-0
Hunter, S. K. (2009). Sex differences and mechanisms of task-specific muscle fatigue. Exercise and Sport Sciences Reviews, 37(3), 113-122. doi: 10.1097/JES.0b013e3181aa63e2
Ito, M., Akima, H., & Fukunaga, T. (2000). In vivo moment arm determination using B-mode ultrasonography. Journal of Biomechanics, 33(2), 215-218. doi: http://dx.doi.org/10.1016/S0021-9290(99)00154-2
Kraushaar, B. S., & Nirschl, R. (1999). Current concepts review: tendinosis of the elbow (tennis elbow). Journal of Bone and Joint Surgery, 81, 259-278.
Kubo, K., Kanehisa, H., & Fukunaga, T. (2003). Gender differences in the viscoelastic properties of tendon structures. European Journal of Applied Physiology, 88(6), 520-526. doi: 10.1007/s00421-002-0744-8
Kubo, K., Kanehisa, H., Kawakami, Y., & Fukunaga, T. (2001). Influence of static stretching on viscoelastic properties of human tendon structures in vivo. Journal of Applied Physiology, 90(2), 520-527.
Kubo, K., Kanehisa, H., Kawakami, Y., & Fukunaga, T. (2001). Influences of repetitive muscle contractions with different modes on tendon elasticity in vivo. J Appl Physiol (1985), 91(1), 277-282.
Lewis Jr, R. W. (2013). The effects of intermittent isometric fatigue on concentric, eccentric, and isometric torque.
Lin, T. W., Cardenas, L., & Soslowsky, L. J. (2004). Biomechanics of tendon injury and repair. Journal of Biomechanics, 37(6), 865-877. doi: http://dx.doi.org/10.1016/j.jbiomech.2003.11.005
Linnamo, V., Bottas, R., & Komi, P. (2000). Force and EMG power spectrum during and after eccentric and concentric fatigue. Journal of Electromyography and Kinesiology, 10(5), 293-300.
Ljung, B. O., Friden, J., & Lieber, R. L. (1999). Sarcomere length varies with wrist ulnar deviation but not forearm pronation in the extensor carpi radialis brevis muscle. Journal of Biomechanics, 32(2), 199-202.
Loren, G. J., Shoemaker, S. D., Burkholder, T. J., Jacobson, M. D., Friden, J., & Lieber, R. L. (1996). Human wrist motors: biomechanical design and application to tendon transfers. Journal of Biomechanics, 29(3), 331-342.
Mañanas, M., Rojas, M., Mandrile, F., & Chaler, J. (2005). Evaluation of muscle activity and fatigue in extensor forearm muscles during isometric contractions. Paper presented at the Engineering in Medicine and Biology Society, 2005. IEEE-EMBS 2005. 27th Annual International Conference of the.
Maganaris, C. N., & Paul, J. P. (1999). In vivo human tendon mechanical properties. The Journal of physiology, 521(1), 307-313.
Marshall, M. M., Mozrall, J. R., & Shealy, J. E. (1999). The Effects of Complex Wrist and Forearm Posture on Wrist Range of Motion. Human Factors: The Journal of the Human Factors and Ergonomics Society, 41(2), 205-213. doi: 10.1518/001872099779591178
Mogk, J. P., & Keir, P. J. (2003). The effects of posture on forearm muscle loading during gripping. Ergonomics, 46(9), 956-975. doi: 10.1080/0014013031000107595
Muramatsu, T., Muraoka, T., Takeshita, D., Kawakami, Y., Hirano, Y., & Fukunaga, T. (2001). Mechanical properties of tendon and aponeurosis of human gastrocnemius muscle in vivo. Journal of Applied Physiology, 90(5), 1671-1678.
Oatis, C. (2004). Kynesiology: The Mechanics and Pathomechanics of Human Movement. Kynesiology: The Mechanics and Pathomechanics of Human Movement-0781755131-66, 97.
Öberg, T. (1995). Muscle fatigue and calibration of EMG measurements. Journal of Electromyography and Kinesiology, 5(4), 239-243. doi: http://dx.doi.org/10.1016/1050-6411(96)85582-9
Orizio, C., Diemont, B., Esposito, F., Alfonsi, E., Parrinello, G., Moglia, A., & Veicsteinas, A. (1999). Surface mechanomyogram reflects the changes in the mechanical properties of muscle at fatigue. European Journal of Applied Physiology and Occupational Physiology, 80(4), 276-284.
Piligian, G., Herbert, R., Hearns, M., Dropkin, J., Landsbergis, P., & Cherniack, M. (2000). Evaluation and management of chronic work-related musculoskeletal disorders of the distal upper extremity. American Journal of Industrial Medicine, 37(1), 75-93.
Rettig, A. C. (1994). Wrist problems in the tennis player. Medicine and Science in Sports and Exercise, 26(10), 1207-1212.
Rojas, M., Mananas, M. A., Muller, B., & Chaler, J. (2007). Activation of forearm muscles for wrist extension in patients affected by lateral epicondylitis. Conference Proceedings of the Annual International Conference of the IEEE Engineering in Medicine and Biology Society, 2007, 4858-4861. doi: 10.1109/iembs.2007.4353428
Ryschon, T., Fowler, M., Wysong, R., Anthony, A.-R., & Balaban, R. (1997). Efficiency of human skeletal muscle in vivo: comparison of isometric, concentric, and eccentric muscle action. Journal of Applied Physiology, 83(3), 867-874.
Semmler, J. G., Tucker, K. J., Allen, T. J., & Proske, U. (2007). Eccentric exercise increases EMG amplitude and force fluctuations during submaximal contractions of elbow flexor muscles. Journal of Applied Physiology, 103(3), 979-989.
Shiri, R., & Viikari-Juntura, E. (2011). Lateral and medial epicondylitis: role of occupational factors. Best Practice & Research: Clinical Rheumatology, 25(1), 43-57. doi: 10.1016/j.berh.2011.01.013
Strickler, T., Malone, T., & Garrett, W. E. (1990). The effects of passive warming on muscle injury. American Journal of Sports Medicine, 18(2), 141-145.
Sugisaki, N., Kawakami, Y., Kanehisa, H., & Fukunaga, T. (2011). Effect of muscle contraction levels on the force-length relationship of the human Achilles tendon during lengthening of the triceps surae muscle-tendon unit. Journal of Biomechanics, 44(11), 2168-2171. doi: 10.1016/j.jbiomech.2011.05.015
Taylor, J. L., Allen, G. M., Butler, J. E., & Gandevia, S. C. (2000). Supraspinal fatigue during intermittent maximal voluntary contractions of the human elbow flexors. J Appl Physiol (1985), 89(1), 305-313.
Taylor, J. L., & Gandevia, S. C. (2008). A comparison of central aspects of fatigue in submaximal and maximal voluntary contractions. Journal of Applied Physiology, 104(2), 542-550.
Unyo, C., Chaler, J., Rojas-Martinez, M., Pujol, E., Muller, B., Garreta, R., & Mananas, M. A. (2013). A cross-sectional study comparing strength profile of dorsal and palmar flexor muscles of the wrist in epicondylitis and healthy men. European Journal of Physical and Rehabilitation Medicine, 49(4), 507-515.
Vollestad, N. K. (1997). Measurement of human muscle fatigue. Journal of Neuroscience Methods, 74(2), 219-227.
Vollestad, N. K., Sejersted, I., & Saugen, E. (1997). Mechanical behavior of skeletal muscle during intermittent voluntary isometric contractions in humans. J Appl Physiol (1985), 83(5), 1557-1565.
Wang, H. K., Lin, K. H., Su, S. C., Shih, T. T., & Huang, Y. C. (2012). Effects of tendon viscoelasticity in Achilles tendinosis on explosive performance and clinical severity in athletes. Scandinavian Journal of Medicine and Science in Sports, 22(6), e147-155. doi: 10.1111/j.1600-0838.2012.01511.x
Warren, C. G., Lehmann, J. F., & Koblanski, J. N. (1971). Elongation of rat tail tendon: effect of load and temperature. Archives of Physical Medicine and Rehabilitation, 52(10), 465-474 passim.
Willoughby, D. S., & Taylor, L. (2004). Effects of concentric and eccentric muscle actions on serum myostatin and follistatin-like related gene levels. Journal of Sports Science and Medicine, 3, 226-233.
Wojtys, E. M., Wylie, B. B., & Huston, L. J. (1996). The effects of muscle fatigue on neuromuscular function and anterior tibial translation in healthy knees. The American journal of sports medicine, 24(5), 615-621.
Zhang, L. Q., & Rymer, W. Z. (2001). Reflex and intrinsic changes induced by fatigue of human elbow extensor muscles. Journal of Neurophysiology, 86(3), 1086-1094.
Zhao, H., Ren, Y., Wu, Y. N., Liu, S. Q., & Zhang, L. Q. (2009). Ultrasonic evaluations of Achilles tendon mechanical properties poststroke. J Appl Physiol (1985), 106(3), 843-849. doi: 10.1152/japplphysiol.91212.2008