COMMON PROTECTIVE MOVEMENTS GOVERN UNEXPECTED FALLS FROM STANDING HEIGHT

Simple energy considerations suggest that any fall from standing heigh t has the potential to cause hip fracture. However, only 1-2% of falls among the elderly actually result in hip fracture, and less than 10% cause serious injury. This suggests that highly effective movement str ategies exist for preventing injury during a fall. To determine the na ture of these, we measured body segment movements as subjects (aged 22 -35 yr) stood upon a gymnasium mattress and attempted to prevent thems elves from falling after the mattress was made to translate abruptly. Subjects were more than twice as likely to fall after anterior transla tions of the feet, when compared to posterior or lateral translations. In falls which resulted in impact to the pelvis, a complex sequence o f upper extremity movements allowed subjects to impact their wrist at nearly the same instant as the pelvis (average time interval between c ontacts = 38 ms), suggesting a sharing of contact energy between the t wo body parts. Finally, marked trunk rotation was exhibited in falls d ue to lateral (but not anterior or posterior) perturbations, resulting in the avoidance of impact to the lateral aspect of the hip. These re sults suggest that body segment movements during falls, rather than be ing random and unpredictable, involve a repeatable series of responses which facilitate safe landing. (C) 1998 Elsevier Science Ltd. All rig hts reserved.