At least 280,000 hip fractures occur annually in the U.S., at an estimated cost of $9 billion. While over 90% of these are caused by falls, only about 2% of all falls result in hip fracture. Considerable evidence now exists that the most important determinants of hip fracture risk during a fall are the body's impact velocity and configuration (and in particular, whether contact occurs to the hip region). Accordingly, protective responses for reducing impact velocity, and the likelihood for direct impact to the hip, strongly influence fracture risk. Improved understanding of the nature of such responses, and how these are affected by age-related declines in neuromuscular variables, would enhance our ability to develop exercise- based strategies for hip fracture prevention. Based on the results of epidemiological and biomechanical studies, we hypothesize that two protective responses central to safe landing during a fall are (a) absorbing energy in the lower extremity muscles during the descent phase of the fall, and (b) braking the fall with the outstretched hands. We also hypothesize, based on epidemiological evidence, that the efficacy of these responses associate with strength, flexibility, and reaction time. To test these hypotheses, we will address four aims.
Aim 1 is to test whether use of the above protective responses influences young females' ability to avoid impact to the hip, and reduce the impact velocity of the body during falls onto a soft gymnasium mat.
Aim 2 is to test whether ancillary measures of balance and lower extremity flexibility and reaction time associate with young and elderly subjects' ability to absorb energy in their lower extremity muscles, and reduce impact velocity when descending from standing to sitting.
Aim 3 is to test whether balance and upper extremity strength, flexibility, and reaction time associate with young and elderly subjects' ability to quickly contact an impact surface with the outstretched hands, and absorb energy in the upper extremity muscles during simulated falls. Finally, Aim 4 is to develop and validate complementary mathematical models of falling, and use these to determine how specific impairments (or exercise-induced enhancements) in muscle strength, joint flexibility. Finally, Aim 4 is to develop and validate complementary mathematical models of falling, and use these to determine how specific impairments (or exercise-induced enhancements) in muscle strength, joint flexibility, and reaction time affect fall protective responses and fall severity. By identifying the biomechanical and neuromuscular variables which govern safe landing during a fall, these studies should lead to novel and effective interventions for reducing hip fractures in the elderly.

Agency
National Institute of Health (NIH)
Institute
National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS)
Type
Research Project (R01)
Project #
5R01AR046890-02
Application #
6375318
Study Section
Geriatrics and Rehabilitation Medicine (GRM)
Program Officer
Panagis, James S
Project Start
2000-09-20
Project End
2003-08-31
Budget Start
2001-09-01
Budget End
2002-08-31
Support Year
2
Fiscal Year
2001
Total Cost
$193,669
Indirect Cost
Name
University of California San Francisco
Department
Orthopedics
Type
Schools of Medicine
DUNS #
073133571
City
San Francisco
State
CA
Country
United States
Zip Code
94143
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Tan, Juay-Seng; Eng, Janice J; Robinovitch, Stephen N et al. (2006) Wrist impact velocities are smaller in forward falls than backward falls from standing. J Biomech 39:1804-11
Mackey, Dawn C; Robinovitch, Stephen N (2006) Mechanisms underlying age-related differences in ability to recover balance with the ankle strategy. Gait Posture 23:59-68
Robinovitch, Stephen N; Normandin, Sarah C; Stotz, Paula et al. (2005) Time requirement for young and elderly women to move into a position for breaking a fall with outstretched hands. J Gerontol A Biol Sci Med Sci 60:1553-7
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Robinovitch, Stephen N; Brumer, Rebecca; Maurer, Jessica (2004) Effect of the ""squat protective response"" on impact velocity during backward falls. J Biomech 37:1329-37
Robinovitch, Stephen N; Inkster, Lisa; Maurer, Jessica et al. (2003) Strategies for avoiding hip impact during sideways falls. J Bone Miner Res 18:1267-73
Robinovitch, Stephen N; Heller, Britta; Lui, Andrew et al. (2002) Effect of strength and speed of torque development on balance recovery with the ankle strategy. J Neurophysiol 88:613-20
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