2012.03.12: Jessica Allen - Insights into impaired muscular coordination post-stroke using musculoskeletal modeling

Stroke is a leading cause of long-term disability that often leaves survivors with various levels of hemiparesis that affects their mobility. Individuals with post-stroke hemiparesis typically walk asymmetrically and at slower speeds due to impaired muscular coordination; however, the type of coordination impairment can vary among patients. Musculoskeletal modeling and simulation techniques are powerful tools that allow us to examine the complex relationship between muscle coordination and walking performance. This talk will focus on using a combined experimental and modeling approach to gain insight into the effect of different coordination impairments on post-stroke hemiparetic gait. Understanding how these different coordination impairments affect specific measures of walking performance (e.g. supporting the body, generating propulsion and maintaining balance) has important implications for designing locomotor therapies that target specific functional deficits and improve rehabilitation outcomes.

• Model is built in SIMM
  • Hill muscle model
    • low-pass filter activation dynamics
  • 38 muscles per leg
• Using simulated-annealing to find "optimal" muscle patterns
• Ankle plantar-flexors are very important in order for forward propulsion for hemiparetic stroke subjects
• Asymmetry in shear ground reaction forces can be an indicator of ankle strength in stroke survivors.
• Contralateral hamstrings are likely used to contribute to swing initiation.
• Decomposition of modules during walking divides up the modules into the time-components of gait of body support, forward propulsion and leg swing
  • Strike, stance, push-off, swing
• 3D model with synergies were used to look for modules for: braking, propulsion, body support , ml balance, leg swing
  • Early stance module was seen for medial-lateral balance
  • Late stance module for power generation?
  • Swing
  • Late swing also mediolateral balance
• In stroke it appears that modules associated with stance are merged.
  • Can we use mathematical definitions of stability to determine changes between these conditions?
  • Knee extensors, hip flexors and ankle plantar-flexors are all merged together which increases braking and decreases forward propulsion in one group.
  • Co-contraction of quads and hamstrings affected body support and mediolateral balance in the other group.
    • Do you see an observational sway of CoM medially in these stroke survivors?
• What about perceived loss in muscle strength?
• What are the big things that affect these people's mobility?
• Coordination of muscles across legs?
  • Compensation by the contralateral limb?
• What about the sensory feedback impairment?