Background　MRI-based　finite　element　analysis　(MRI-FEA)　is　the　only　method　able　to　assess　microstructural　and　whole-bone　mechanical　properties　of　the　hip　in　vivo.　Purpose　To　examine　whether　MRI-FEA　is　capable　of　discriminating　age-related　changes　in　whole-bone　mechanical　performance　and　micromechanical　behavior　of　the　proximal　femur,　particularly　considering　the　most　common　hip　fracture-related　sideways　fall　loading.　Study　Type　Retrospective.　Subjects　A　total　of　nine　younger　(27　+/-　3.2　years)　and　nine　elderly　(61　+/-　3.9　years)　healthy　volunteers.　Field　Strength/Sequence　3T;　3D　fast　field　echo　sequence.　Assessment　The　left　proximal　femurs　were　scanned　and　FE　models　created.　FEA　was　performed　to　simulate　sideways　fall　and　stance　loading　for　each　femoral　model.　Apparent　stiffness　and　high-risk　(90th　percentile)　tensile　and　compressive　strains　of　the　proximal　femur　as　well　as　the　average　strains　within　cubic　regions　of　the　femoral　neck　and　greater　trochanter　were　assessed.　Statistical　Tests　Paired　and　unpairedt-tests.　Results　Compared　to　the　young　group,　the　femoral　stiffness　of　the　elderly　decreased　by　39%　and　40%　(bothP　＜　0.05)　under　the　sideways　fall　and　stance　conditions,　respectively.　Accordingly,　the　high-risk　tensile　and　compressive　stains　were　elevated　with　aging　(40%　and　23%　for　sideways　fall,　23%　and　11%　for　stance　conditions;　allP　＜　0.05).　However,　the　loading　configuration-induced　difference　was　only　observed　in　the　elderly　group　for　the　high-risk　strains　(22%　for　tension　and　12%　for　compression;　bothP　＜　0.05).　Additionally,　compared　to　the　stance　condition,　the　sideways　fall　increased　the　average　tensile　(young:　108%,　elderly:　123%;　bothP　＜　0.05)　and　compressive　strains　(young:　631%,　elderly:　617%,　bothP　＜　0.05)　within　the　greater　trochanter　rather　than　the　femoral　neck　region.　Data　Conclusion　In　vivo　MRI-FEA　is　capable　of　capturing　age-related　changes　in　both　apparent-level　stiffness　and　tissue-level　micromechanical　behavior　of　the　proximal　femur.　However,　the　effect　of　sideways　fall　loading　might　be　better　reflected　by　tissue-level　micromechanics　rather　than　apparent　stiffness.　Level　of　Evidence　3　Technical　Efficacy　Stage　1