Effect of Muscle Fatigue on Biomechanical Behavior of Common Extensor Tendon

Abstract

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

Date of Award	2014 Aug 21
Original language	English
Supervisor	Fong-chin Su (Supervisor)