Project 1:​ Femoral neck is of particular concern in the hip fractures andaging. Abetter understanding of the hip loading environment is helpful for the hi pfracture prevention, rehabilitation, and the design of osteogenic exercises. This study wastocompare the femoral neck stresses between young and older adults during stair ascent and descent, and to identify the contribution of muscle and reaction forces to thestress. Motion analysis and inverse dynamics method, musculoskeletal and elliptical femoral neck cross-section models were used to estimate stress on the femoral neck. During stair ascent, a significantly increased tension at the superior site was found for young group at the first peak (young:​ 13.5±6.1 MPa, old:​ 4.2±6.5 MPa, p < 0.001), and a significantly increased compression at the posterior site for old group at the second peak (young:​ -11.4±4.9 MPa, old:​ -18.1±8.6 MPa, p = 0.006). The stresses produced by muscle and reaction forces were reported for all 4 surfaces of the femoral neck. The loadingof theproximal femur as assessed from stresses and their component provided loading information on the bone structure. Understanding this information can provide the researcher with a more comprehensive view of the loading on the bone tissues in the hip region.

Project 2:​ Understanding the hip loading environment during daily activity is necessary for the understanding of hip fractures and the design of osteogenic exercises. Using the finite element femur model, the purpose of this study was to estimate the femoral strains at 9 cross-sections along the long axis of femur for stair ascent and descent at the hip contact force peaks. All subjects (both young and older groups) performed 5 trials of stair ascent and 5 trials of descent with a 3-step staircase. For the compressive strains, stair descent generated greater compressive strains than ascent forall cross-sections (except the 8th cross-section) during both hip joint contact force peak 1 and peak 2. For the tensile strains, stair descent generated greater tensile strains thanascent for most cross-sections during both hip joint contact force peak 1 (the 1st to6th, and the 9th cross-sections) and peak 2 (the 1st to 6th, the 7th, and the 9th cross-sections). Strains were analyzed in this study, which represents the material deformation effect on the bone due to the sum of all the bone external loads. Using bone strains could help future studies analyze loading conditions in a more comprehensive way for other physical activities, which predicts the risk of stress fractures and tests if some alternative methods (gait type change) could reducestressand strain effectively.

Project 3:​ For older population, development of hip fracture and pain prevention, and the design of osteogenic exercise need better understanding of the hip joint loadin genvironment during daily activities. Using the motion analysis and inverse dynamics methods, combined with musculoskeletal modelling, static optimization, and finite element femur model, this study is to compare the femoral neck strains between stair ascent and descent, young and older populations. The strains at the femoral neckcross-section were greater for stair descent than ascent for young (Compressive:​ peak1 descent -806.6±363.6 µε, ascent -500.1±137.5 µε, p<0.001;​ peak 2 descent -679.3±301.2 µε, ascent -401.8±132.7 µε, p<0.001;​ Tensile:​ peak 1 descent 339.3±195.0 µε, ascent176.8±68.5 µε, p=0.001;​ peak 2 descent 259.0±99.3 µε, ascent 123.9±46.7 µε, p=0.004) and older groups (Compressive:​ peak 1 descent -564.7±177.2 µε, ascent -403.6±144.8µε, p=0.006;​ peak 2 descent -503.3±155.9 µε, ascent -386.3±127.7 µε, p<0.001;​ Tensile:​ peak 1 descent 236.7±105.3 µε, ascent 136.1±65.3 µε, p=0.003;​ peak 2descent208.7±75.1 µε, ascent 126.0±46.5 µε, p<0.001). Strain represents the material deformation of the bone due to the sum of all the external loads. Using bone strains could analyze bone loading in more comprehensive ways during physical activities, which predicts the risk of stress fractures and tests the possible preventative methods.

Project 4:​ This research focused on stair descent to explore the loading environment of the femoral neck, and develop some methods which might reducefemoral neck loads in the daily activities. Using the motion analysis and inverse dynamics methods, combined with musculoskeletal modelling, static optimization, and finite element femur model, maximum compressive and tensile strains were tested at the femoral neck using different gait types (step over step, step by step) and different external weight carrying strategies (10% of body weight at ipsilateral side, 10% at contralateral side) during stair descent. There is no significant Pearson Correlation between age and femoral neck strains. The best Pearson Correlation (R=-0.282) between age and compressive strain was found for the condition of step-over-step with external weight at the ipsilateral side during the 2nd peak of hip joint contact force. Compared with step-over-step, the compressive strain was significantly reducedfor step-by-step with the trailing leg for the 1st peak (trailing:​ -739.6±184.0 µε, step-over-step:​ -852.1±213.9 µε, p<0.001, d=0.70). Contralateral side weight carrying increased both compressive and tensile strains for both step-over-step and step-by-step strategies than ipsilateral. In general, applying step-by-step method for the trailing leg and avoid external weight carrying at contralateral side could be effective to reduce femoral neck strains.