Muscles, tendons, and ligaments have spring-like characteristics. Because these musculoskeletal elements change length when joints flex or extend, it is not surprising that joints exhibit spring-like characteristics. The control of musculoskeletal stiffness is complex with many factors affecting the stiffness of each joint. However, in some multi-jointed movements, including mammalian running, the elements of the musculoskeletal system are integrated together so that the overall musculoskeletal system exhibits spring-like behavior. Experimental findings on the mechanics of running gaits have revealed that the overall musculoskeletal system behaves like a single linear spring in all of the mammals studied to date, including running humans, trotting dogs and horses, and hopping kangaroos. This observation has led to the development of a spring-mass model for running, consisting of a single linear massless """"""""leg spring"""""""" and a mass. The """"""""leg spring"""""""" represents the spring-like characteristics of the overall integrated musculoskeletal system during locomotion, and the mass is equivalent to the mass of the animal. The general objective of the proposed research is to gain an understanding of the link between musculoskeletal stiffness and locomotion biomechanics. Given the complexity of the control of the stiffness of a single muscle or joint, it is not realistic to use a forward dynamics approach that begins at the level of the stiffness-of a single muscle and attempts to explain the mechanics of running. We propose to use an inverse dynamics approach that begins by focusing on the link between locomotion mechanics and overall musculoskeletal stiffness. Under the umbrella of Specific Aim 1, the importance of adjustments to the stiffness of the overall musculoskeletal system to accommodate running on varied terrain is examined. This research will involve examining the adjustments to musculoskeletal stiffness for running on surfaces of different stiffnesses and surfaces of varying predictability. Under the umbrella of Specific Aim 2, we will do a series of interrelated studies examining the mechanisms for adjusting the stiffness of the overall musculoskeletal system during running. These studies will include examining the range over which the stiffness of a single joint of the leg can be adjusted during locomotion. In addition, it will involve examining the relative importance of changes to joint stiffness and posture in adjusting the stiffness of the overall musculoskeletal system during running. The experiments under both Specific Aims l and 2 will involve a combined kinetic and kinematic analysis of running to determine overall musculoskeletal stiffness and joint stiffness. The findings will give new information about the optimal design of floors and tracks for minimizing overuse injuries during sustained weight-bearing aerobic activities, and the optimal design of spring-based prosthetic legs and robotic legs. Finally, our research will begin applying knowledge of the neural control of joint stiffness to understanding the mechanics of a natural activity that is performed by all legged animals, locomotion.

Agency
National Institute of Health (NIH)
Institute
National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS)
Type
First Independent Research Support & Transition (FIRST) Awards (R29)
Project #
7R29AR044008-06
Application #
6446634
Study Section
Special Emphasis Panel (ZRG4-GRM (01))
Program Officer
Panagis, James S
Project Start
1996-04-15
Project End
2003-03-31
Budget Start
2001-02-02
Budget End
2003-03-31
Support Year
6
Fiscal Year
2000
Total Cost
$96,199
Indirect Cost
Name
University of Colorado at Boulder
Department
Physiology
Type
Schools of Arts and Sciences
DUNS #
City
Boulder
State
CO
Country
United States
Zip Code
80309
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Moritz, Chet T; Farley, Claire T (2006) Human hoppers compensate for simultaneous changes in surface compression and damping. J Biomech 39:1030-8
Moritz, Chet T; Greene, Spencer M; Farley, Claire T (2004) Neuromuscular changes for hopping on a range of damped surfaces. J Appl Physiol 96:1996-2004
Moritz, Chet T; Farley, Claire T (2003) Human hopping on damped surfaces: strategies for adjusting leg mechanics. Proc Biol Sci 270:1741-6
Ferris, D P; Aagaard, P; Simonsen, E B et al. (2001) Soleus H-reflex gain in humans walking and running under simulated reduced gravity. J Physiol 530:167-80
Ferris, D P; Liang, K; Farley, C T (1999) Runners adjust leg stiffness for their first step on a new running surface. J Biomech 32:787-94
Farley, C T; Morgenroth, D C (1999) Leg stiffness primarily depends on ankle stiffness during human hopping. J Biomech 32:267-73
Ferris, D P; Louie, M; Farley, C T (1998) Running in the real world: adjusting leg stiffness for different surfaces. Proc Biol Sci 265:989-94
Farley, C T; Houdijk, H H; Van Strien, C et al. (1998) Mechanism of leg stiffness adjustment for hopping on surfaces of different stiffnesses. J Appl Physiol 85:1044-55
Lee, C R; Farley, C T (1998) Determinants of the center of mass trajectory in human walking and running. J Exp Biol 201:2935-44

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