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dc.contributorDepartment of Rehabilitation Sciencesen_US
dc.contributor.advisorFu, Siu-ngor (RS)en_US
dc.creatorXu, Jingfei-
dc.publisherHong Kong Polytechnic Universityen_US
dc.rightsAll rights reserveden_US
dc.titleDivergence on muscle stiffness of individual muscle heads of the quadriceps femoris muscleen_US
dcterms.abstractThe quadriceps femoris muscle relies on the synchronized action of its four muscle heads, controls the position and movement of the patella–femoral and tibio–femoral knee joints. Dissimilarity of structure and function have been reported on individual heads of the quadriceps femoris muscle. Divergence on their mechanical properties might cause mal-alignments of the patella–femoral and tibio–femoral knee joints and might affect muscle function and performance. Hence, the overall objective of the study was to investigate whether modulation on mechanical properties of quadriceps femoris muscle would be muscle-head specific. In order to address this objective, four inter-related studies were conducted. The superficial muscle heads of interest were the vastus medialis (VM), rectus femoris (RF), and vastus lateralis (VL) muscles. Muscle shear modulus (an index of stiffness) was measured using shear wave elastography. Study 1 aimed to determine the passive stiffness–angle relationship and the slack angle of the three muscle heads and to explore whether this differs between muscle heads. Study 2 aimed to study aging effects by comparing the (1) passive shear modulus of the three muscle heads at 30°, 60°, and 90° of knee flexion and (2) active shear modulus of these muscle heads during isometric contraction (30% of maximal isometric voluntary contraction (MIVC)) at 30°, 60° and 90° of knee flexion between 20 healthy young and 20 senior females. Study 3 had a similar study design as study 2 and comparison on the outcome measures were conducted between 20 healthy females and 10 males. The effect of eccentric exercise on passive muscle stiffness was explored in study 4. Whether a bout of eccentric exercise would change the passive stiffness of individual heads of quadriceps femoris muscle homogenously was determined and whether pre-exercise muscle stiffness is related to the force loss observed after a bout of eccentric knee extensions at immediately post- and 48 hours post-exercise on 50 young healthy subjects was explored. Results from the 4 studies indicate a divergence in response to joint positioning, aging, gender and post eccentric exercises modulation on passive muscle stiffness among the muscle heads of the quadriceps femoris muscles. The study showed that the shear modulus of RF muscle was higher than that of VM and VL when the muscles were stretched over 54°. No significant difference was found between the VM and VL. The slack angle was similar among the muscle heads which was just over 40° of knee flexion. Senior females presented significantly higher passive shear modulus in RF and VL muscle heads at long muscle length (60° and 90° of knee flexion) than the younger females.en_US
dcterms.abstractIn addition, the RF passive shear modulus could predict 28.3% of the MIVC measured at 60° of knee flexion across the age groups. A bout of eccentric exercise induced significant increase of passive shear modulus of RF muscle at long length (90° of knee flexion). Slight but significant decrease in VL passive shear modulus was observed at 30° and 60° knee flexion. No change was observed in VM muscle. The decrease in MIVC at 48 H was negatively correlated with the RF passive shear modulus measured at 90° of knee flexion before the exercise. The RF passive shear modulus was significantly higher for 35% and 42% in young males when it was stretched to a long length (60° and 90° knee flexion, respectively) than young females. The active shear modulus of VM, RF, and VL at 30° knee flexion in senior females was higher than young females by 10%, 20%, and 21%, respectively. Young females exhibited greater active shear modulus of the three muscles than young males at 60° and 90° knee flexion (p = 0.024 and p < 0.001, respectively). From the results of the four studies, the following conclusions could be drawn. (1) In response to passive lengthening beyond the slack angle, the RF muscle head of the quadriceps femoris muscle shows dissimilar response than the VL and VM muscle heads. (2) Dissimilar modulation on muscle stiffness associated with gender and in response to aging and a bout of eccentric exercise is observed when the muscle heads are positioned beyond its slack angle (at a stretched length). More specifically, the VL and RF muscles but not the VM muscle present greater passive stiffness in senior females than young females; and the RF muscle head shows greater passive stiffness in the young males than young females. A bout of eccentric exercise induces significant increase in the RF passive stiffness. (3) In addition, passive muscle stiffness is associated with muscle function. First, the passive muscle stiffness of RF is one of the predictors for isometric knee extension force; Second, stiffer RF may induce greater muscle damage associated with a bout of eccentric exercise at 48 H after exercise. Taken together, "appropriate" passive stiffness of the RF muscle stiffness is essential for the function of the quadriceps femoris on isometric and eccentric muscle work. Active muscle stiffness associated with submaximal isometric contraction is similar among the three superficial muscle heads of the quadriceps femoris muscle.en_US
dcterms.extentxvi, 147 pages : color illustrationsen_US
dcterms.educationalLevelAll Doctorateen_US
dcterms.LCSHQuadriceps muscleen_US
dcterms.LCSHMuscle strengthen_US
dcterms.LCSHMuscle contractionen_US
dcterms.LCSHHong Kong Polytechnic University -- Dissertationsen_US
dcterms.accessRightsopen accessen_US

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