Background: A hip fracture may occur spontaneously prior to the hip impact, due to the muscle pulling force exceeding the strength of the femur.
Objects: We conducted falling experiments with humans to measure the activity of the hip muscles, and to examine how this was affected by the fall type.
Methods: Eighteen individuals fell and landed sideways on a mat, by mimicking video-captured real-life older adults’ falls. Falling trials were acquired with three fall directions: forward, backward, or sideways, and with three knee positions at the time of hip impact, where the landing side knee was free of constraint, or contacted the mat or the contralateral knee. During falls, the activities of the iliopsoas (Ilio), gluteus medius (Gmed), gluteus maximus (Gmax) and adductor longus (ADDL) muscles were recorded. Outcome variables included the time to onset, activity at the time of hip impact, and timing of the peak activity with respect to the time of hip impact.
Results: For Ilio, Gmed, Gmax, and ADDL, respectively, EMG onset averaged 292, 304, 350, and 248 ms after fall initiation. Timing of the peak activity averaged 106, 96, 84, and 180 ms prior to the hip impact, and activity at the time of hip impact averaged 72.3, 45.2, 64.3, and 63.4% of the peak activity. Furthermore, the outcome variables were associated with fall direction and/or knee position in all but the iliopsoas muscle.
Conclusion: Our results provide insights on the hip muscle activation during a fall, which may help to understand the potential injury mechanism of the spontaneous hip fracture.

INTRODUCTION
MATERIALS AND METHODS
    1. Subjects
    2. Experimental Protocol and Equipment
    3. Data Analysis
RESULTS
    1. One-way ANOVA
    2. Two-way ANOVA
DISCUSSION
CONCLUSIONS
REFERENCES

• Kwang Jun Lee(Department of Physical Therapy, Injury Prevention and Biomechanics Laboratory, Yonsei University)
• Kitaek Lim(Department of Physical Therapy, Injury Prevention and Biomechanics Laboratory, Yonsei University)
• Woochol Joseph Choi(Department of Physical Therapy, Injury Prevention and Biomechanics Laboratory, Yonsei University) Corresponding Author