Short communicationMartial arts fall techniques decrease the impact forces at the hip during sideways falling
Introduction
Hip fracture is a serious consequence of falls in elderly people. About 90% of hip fractures are caused by falls (Cumming and Klineberg, 1994). In particular falls to the side and those with impact on the hip have an increased risk for hip fractures. Interventions that reduce the fall severity of these more dangerous falls are expected to decrease the risk of fractures (Greenspan et al., 1994; Nevitt and Cummings, 1993).
Experimental fall studies have shown that to avoid hip impact during a sideways fall, young subjects use their hands and rotate the trunk (Hsiao and Robinovitch, 1998). For elderly, using the hands is not without risk, as hand impact increases the risk for wrist fractures (Nevitt and Cummings, 1993). Relaxing the body during descent could reduce the impact velocity (van den Kroonenberg et al., 1996), but not the hip impact force (Sabick et al., 1999). In contrast, a martial arts (MA) fall technique has been shown to reduce the hip impact force as compared to ‘normal’ tensed falls (Sabick et al., 1999). Knowledge about the working mechanism and the potential benefits for elderly to learn the MA fall techniques is limited, but is needed since MA fall techniques are being successfully used in programs to prevent falls in elderly (Rijken et al., 2005). The high impact force at the hand that is used to break the MA fall have raised concerns (DeGoede et al., 2003). It was suggested that hand impact would play a role in the reduction of hip impact force (Sabick et al., 1999); however, it has not been proven. Hence, experiments are needed to determine if hand impact is essential to reduce hip impact force.
According to simple impact models, hip impact force is determined by hip impact velocity, the effective mass of that part of the body that is moving prior to impact, and the overall stiffness of the soft tissue overlying the hip (van den Kroonenberg et al., 1995). The effective mass is dependent on trunk orientation at impact in such a way that the more vertical the trunk, the larger the effective mass. Hence, other factors that may play a role in the reduction of hip impact by the MA technique are impact velocity and trunk orientation.
The purpose of this study was to get insight into the mechanism by which MA fall techniques would reduce hip impact force during sideways falls. The hypothesis was that the presence of hand impact, a decreased impact velocity and a more horizontal trunk orientation would provide an explanation. In addition, the time curves of the different fall techniques were examined to detect temporal differences and to investigate if changes were attributable to certain kinematic or kinetic events.
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Methods
Six experienced judokas participated (age: 24.2±3.8 years, weight: 65.8±19.6 kg, experience: 13.0±6.8 years) and signed informed consent prior to participation. The protocol was approved by the Ethical Board of the region Arnhem-Nijmegen.
Forces were measured with a force plate (Kistler, size 0.6 m×0.4 m) at 2400 Hz. The 3D positions of reflective markers were simultaneously registered with a 6-camera motion analysis system (Primas) at 100 Hz. Markers were placed on the left shoulder, wrist, and
Results
The largest mean hip impact forces and velocities and the most vertical trunk orientations were found for the Block falls (Fig. 2). The Friedman test revealed a main effect of technique on hip impact force (Fr=9.333; ), impact velocity (Fr=10.333; ), and trunk angle (Fr=8.333; ). Post hoc comparisons showed that the MA-a and MA-na technique significantly (both ) reduced the hip impact force by 27.0% and 29.5%, respectively. The impact velocity was significantly lower
Discussion
The results showed that the MA-a and MA-na techniques reduced the hip impact force in sideways falls from kneeling height by 27.5% and 30%, respectively. In comparison, Sabick et al. (1999) found a reduction of 12% as compared to their ‘normal’ tensed condition without hand impact. They suggested that hand impact would be responsible for this reduction. In contrast, our study showed that hand impact is not an essential element of the MA technique in the reduction of hip impact force since no
Acknowledgments
This study was supported by the POM, Nijmegen, the Organization for Healthcare Research in the Netherlands (ZonMW), and an EU Grant (Eurokinesis, QLK6-CT-2002-00151).
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