The pervasive decline in ankle power generation, even in otherwise healthy older adults, plays a central role in the deterioration of walking abilit with age. However, muscle strengthening alone generally fails to significantly improve the walking ability of older adults, suggesting that factors other than sarcopenia contribute to the decline in plantarflexor power with age. I propose to investigate the relevance of age-related changes in Achilles tendon mechanics and their implications for walking ability in older adults. The premise of this study is that the aging Achilles tendon exhibits altered in vivo behavior that greatly diminishes the ability to optimally coordinate the ankle plantarflexor muscles during the push-off phase of gait. Preliminary data suggest that the superficial and deep Achilles tendon fascicles exhibit distinctly different displacements, likely due to inter- fascicle sliding, which ay be critical for optimally coordinating the forces from the individual plantarflexor muscles. Moreover, these data show evidence that advancing age brings much more uniform tendon tissue motion, which may arise from inter-fascicle adhesions within the Achilles tendon. The overall hypothesis of this research is that greater fascicle adhesions within the Achilles tendon of older adults bring more uniform tendon deformations that reduce the capacity for optimally coordinating the individual plantarflexor muscles, thereby compromising plantarflexor power and thus gait performance. The approach utilizes novel advances in imaging biomechanics and computational modeling to investigate age-related changes in Achilles tendon mechanics and function, and to predict the ramifications for walking ability in older adults. Following are the specific aims.
Aim 1 will use an advanced ultrasound elastography approach to determine if advancing age is accompanied by greater Achilles tendon strain uniformity, a potentially important factor to consider as a mechanism for age- related walking ability limitations.
Aim 2 will use an innovative combination of ultrasound elastography and electrical muscle stimulation to reveal if greater fascicle adhesions within the Achilles tendon of older adults bring more uniform deformations between the deep and superficial portions of the tendon. Finally, Aim 3 will incorporate the findings from Aims 1 and 2 into muscle-actuated forward dynamic simulations to predict changes in plantarflexor function during walking in older adults. This research will investigate for the first time the age-related changes in localized Achilles tendon strain distributions (Aim 1), their underlying mechanisms (Aim 2), and the ramifications for walking ability in older adults (Aim 3). Successful completion of these aims will contribute to an enhanced scientific understanding of age-related declines in walking ability and point to specific opportunities where more appropriate therapies could prolong independence and thus enhance quality of life in older adults.

Public Health Relevance

The premise of this study is that the aging Achilles tendon exhibits altered behavior that greatly diminishes the ability to optimally coordinate the ankle plantarflexor muscles during the push-off phase of gait. The experimental approach combines advanced tissue imaging with experimental and computational techniques to investigate age-related changes in Achilles tendon mechanics and how they may compromise walking ability in older adults. The expected results will lead to an enhanced scientific understanding of age-related impairments in walking ability and point to specific opportunities where more appropriate therapies could prolong independent walking ability and thus enhance quality of life in older adults.

Agency
National Institute of Health (NIH)
Institute
National Institute on Aging (NIA)
Type
Postdoctoral Individual National Research Service Award (F32)
Project #
5F32AG044904-02
Application #
8701027
Study Section
Special Emphasis Panel (ZRG1)
Program Officer
Joseph, Lyndon
Project Start
2013-06-01
Project End
2016-05-31
Budget Start
2014-06-01
Budget End
2015-05-31
Support Year
2
Fiscal Year
2014
Total Cost
Indirect Cost
Name
University of Wisconsin Madison
Department
Engineering (All Types)
Type
Biomed Engr/Col Engr/Engr Sta
DUNS #
City
Madison
State
WI
Country
United States
Zip Code
53715
Rasske, Kristen; Franz, Jason R (2018) Aging effects on the Achilles tendon moment arm during walking. J Biomech 77:34-39
Franz, Jason R; Francis, Carrie; Allen, Matt et al. (2017) Visuomotor Entrainment and the Frequency-Dependent Response of Walking Balance to Perturbations. IEEE Trans Neural Syst Rehabil Eng 25:1132-1142
Thompson, Jessica D; Franz, Jason R (2017) Do kinematic metrics of walking balance adapt to perturbed optical flow? Hum Mov Sci 54:34-40
Rasske, Kristen; Thelen, Darryl G; Franz, Jason R (2017) Variation in the human Achilles tendon moment arm during walking. Comput Methods Biomech Biomed Engin 20:201-205
Franz, Jason R; Thelen, Darryl G (2016) Imaging and simulation of Achilles tendon dynamics: Implications for walking performance in the elderly. J Biomech 49:1403-1410
Franz, Jason R (2016) The Age-Associated Reduction in Propulsive Power Generation in Walking. Exerc Sport Sci Rev 44:129-36
Franz, Jason R; Francis, Carrie A; Allen, Matthew S et al. (2015) Advanced age brings a greater reliance on visual feedback to maintain balance during walking. Hum Mov Sci 40:381-92
Franz, Jason R; Slane, Laura C; Rasske, Kristen et al. (2015) Non-uniform in vivo deformations of the human Achilles tendon during walking. Gait Posture 41:192-7
Franz, Jason R; Thelen, Darryl G (2015) Depth-dependent variations in Achilles tendon deformations with age are associated with reduced plantarflexor performance during walking. J Appl Physiol (1985) 119:242-9
Francis, Carrie A; Franz, Jason R; O'Connor, Shawn M et al. (2015) Gait variability in healthy old adults is more affected by a visual perturbation than by a cognitive or narrow step placement demand. Gait Posture 42:380-5