Browsing by Author "Yan, Chenxi"

Now showing 1 - 3 of 3
  • Thumbnail Image
    Item
    Effect of fatigue loading and rest on impact strength of rat ulna
    (Elsevier, 2021-06) Yan, Chenxi; Song, Hyunggwi; Pfister, Jennifer; Andersen, Thomas L.; Warden, Stuart J.; Bhargava, Rohit; Kersh, Mariana E.; Physical Therapy, School of Health and Human Sciences
    Stress fracture is a common injury among athletes and military personnel and is associated with fatigue-initiated damage and impact loading. The recovery of bending strength has been shown to be a function of the rest days allowed after fatigue loading in rodents and the aim of this study was to investigate if similar results would occur under impact conditions. In this study, cyclic axial compression load was applied in vivo on the right forelimbs while left forelimbs served as controls. Two rest groups were used: one day of rest and seven days of rest. Afterwards, all ulnae were scanned using micro-Computed Tomography followed by impact testing. The micro-CT scan confirmed the formation of woven bone on loaded ulnae after seven days rest. The peak impact force was 37.5% higher in the control (mean = 174.96 ± 33.25 N) specimens compared to the loaded bones (mean = 130.34 ± 22.37 N). Fourier-transformed infrared spectroscopy analyses suggested no significant change of chemical composition in the cortical region between the loaded and control ulnae, but woven bone region had lower carbonate and amide I content than contralateral controls (p < 0.05). We find that cyclic fatigue loading had a negative effect on bone’s impact response. Bones that experienced fatigue loading became less stiff, weaker, and more prone to fracture when subjected to impact. The formation of woven bone after seven days of rest did not restore the stiffness upon impact and confirm that rest time is crucial to the recovery of fatigue damage.
  • Thumbnail Image
    Item
    Heterogeneous Spatial and Strength Adaptation of the Proximal Femur to Physical Activity: A Within-Subject Controlled Cross-Sectional Study
    (Wiley, 2020-04) Warden, Stuart J.; Carballido-Gamio, Julio; Weatherholt, Alyssa M.; Keyak, Joyce H.; Yan, Chenxi; Kersh, Mariana E.; Lang, Thomas F.; Fuchs, Robyn K.; Physical Therapy, School of Health and Human Sciences
    Physical activity (PA) enhances proximal femur bone mass, as assessed using projectional imaging techniques. However, these techniques average data over large volumes obscuring spatially heterogeneous adaptations. The current study used quantitative computed tomography, statistical parameter mapping, and subject-specific finite element (FE) modeling to explore spatial adaptation of the proximal femur to PA. In particular, we were interested in adaptation occurring at the superior femoral neck and improving strength under loading from a fall onto the greater trochanter. High/long jump athletes (n=16) and baseball pitchers (n=16) were utilized as within-subject controlled models as they preferentially load their takeoff leg and leg contralateral to their throwing arm, respectively. Controls (n=15) were included, but did not show any dominant-to-nondominant (D-to-ND) leg differences. Jumping athletes showed some D-to-ND leg differences, but less than pitchers. Pitchers had 5.8% (95% CI, 3.9–7.6%) D-to-ND leg differences in total hip volumetric bone mineral density (vBMD), with increased vBMD in the cortical compartment of the femoral neck, and trochanteric cortical and trabecular compartments. Voxel-based morphometry analyses and cortical bone mapping showed pitchers had D-to-ND leg differences within the regions of the primary compressive trabeculae, inferior femoral neck, and greater trochanter, but not the superior femoral neck. FE modeling revealed pitchers had 4.1% (95%CI, 1.4–6.7%) D-to-ND leg differences in ultimate strength under single-leg stance loading, but no differences in ultimate strength to a fall onto the greater trochanter. These data indicate the asymmetrical loading associated with baseball induces proximal femur adaptation in regions associated with weight bearing and muscle contractile forces, and increases strength under single-leg stance loading. However, there were no benefits evident at the superior femoral neck and no measurable improvement in ultimate strength to common injurious loading during aging (i.e. fall onto the greater trochanter) raising questions as to how to better target these variables with PA.
  • Thumbnail Image
    Item
    Multidirectional basketball activities load different regions of the tibia: A subject-specific muscle-driven finite element study
    (Elsevier, 2022) Yan, Chenxi; Bice, Ryan J.; Frame, Jeff W.; Warden, Stuart J.; Kersh, Mariana E.; Physical Therapy, School of Health and Human Sciences
    The tibia is a common site for bone stress injuries, which are believed to develop from microdamage accumulation to repetitive sub-yield strains. There is a need to understand how the tibia is loaded in vivo to understand how bone stress injuries develop and design exercises to build a more robust bone. Here, we use subject-specific, muscle-driven, finite element simulations of 11 basketball players to calculate strain and strain rate distributions at the midshaft and distal tibia during six activities: walking, sprinting, lateral cut, jumping after landing, changing direction from forward-to-backward sprinting, and changing direction while side shuffling. Maximum compressive strains were at least double maximum tensile strains during the stance phase of all activities. Sprinting and lateral cut had the highest compressive (-2,862 ± 662 με and -2,697 ± 495 με, respectively) and tensile (973 ± 208 με and 942 ± 223 με, respectively) strains. These activities also had the highest strains rates (peak compressive strain rate = 64,602 ± 19,068 με/s and 37,961 ± 14,210 με/s, respectively). Compressive strains principally occurred in the posterior tibia for all activities; however, tensile strain location varied. Activities involving a change in direction increased tensile loads in the anterior tibia. These observations may guide preventative and management strategies for tibial bone stress injuries. In terms of prevention, the strain distributions suggest individuals should perform activities involving changes in direction during growth to adapt different parts of the tibia and develop a more fatigue resistant bone. In terms of management, the greater strain and strain rates during sprinting than jumping suggests jumping activities may be commenced earlier than full pace running. The greater anterior tensile strains during changes in direction suggest introduction of these types of activities should be delayed during recovery from an anterior tibial bone stress injury, which have a high-risk of healing complications.