Summary:​ The magnitude of hip impact force during a fall on the ground (i.e., concrete surface) from standing height was determined. We found that this force decreases up to 59%, depending on how they land on the ground.

Introduction:​ We determined the magnitude of hip impact force that humans may experience in the event of a fall from standing height on the ground, in order to examine how the hip impact force was affected by characteristics of a fall.

Methods:​ Twenty subjects mimicked a typical older adults’ falls on a mat. Trials were acquired with three initial fall directions:​ forward, sideways, and backward. Trials were also acquired with three knee positions at the time of hip impact:​ knee together, knee on the mat, and free knee. During falls, attenuated vertical hip impact forces and corresponding depression of the mat were measured via a force plate placed under the mat and motion capture system, respectively. Using a mass-spring model, actual hip impact force and body stiffness during a fall on the ground were estimated.

Results:​ Hip impact force averaged 4.0 kN (SD = 1.7). The hip impact force was associated with knee condition (F = 25.6, p < 0.005), but not with fall direction (F = 0.4, p = 0.599). Compared with “knee on the mat,” hip impact force averaged 59% and 45% greater in “free knee” and “knee together,” respectively (4.6 versus 2.9 kN, p < 0.005;​ 4.3 versus 2.9 kN, p < 0.005). However, the hip impact force did not differ between “free knee” and “knee together (4.6 versus 4.3 kN, p = 0.554).

Conclusion:​ Our results suggest that hip fracture risk during a fall decreases substantially, depending on how they land on the ground, informing the development of safe landing strategies to prevent fall-related hip fractures in older adults.