PROJECT SUMMARY
Cerebral palsy is the most common pediatric motor disorder. The most prevalent subtype, hemiplegic cerebral
palsy (HCP), is characterized by sensorimotor dysfunction on one side of the body, especially affecting the upper
limb. The impaired sensorimotor control of the upper limb can negatively impact educational opportunities,
participation in daily activities, future job prospects, and self-esteem. For this reason, the upper limb, particularly
the hand, is a significant target for occupational and physical therapy. Despite these efforts, substantial functional
deficits in the upper limb often persist into adulthood and contribute to lifelong limitations. A main contributor to
impairment is profound weakness. The relative strength deficits increase with age in children and extend into
adulthood. Unfortunately, the underlying physiological causes of this weakness are not well understood. Possible
contributors to muscle weakness in CP include a diminished ability to voluntarily excite the muscles, excessive
co-activation of antagonists, and altered muscle morphology. The goal of this research is to determine the relative
contributions of these impairment mechanisms to observed weakness in children with HCP.
Each participant will be asked to complete a set of experiments. In the first experiment, possible involuntary
hyperexcitability of hand muscles, as manifested as spasticity, excessive coactivation, or delayed relaxation
time, will be assessed. To quantify spasticity, a custom servo-controlled jig will impose controlled stretch of the
targeted finger muscles through rotation of the metacarpophalangeal (MCP) joints. The spastic reflex response
will be quantified in terms of resistance torque and activation of finger muscles, as measured with surface
electromyography (EMG). Coactivation and relaxation time will be measured from EMG signals recorded during
voluntary isometric torque generation about the MCP joints with the hand fixed within the jig. Isokinetic
contractions will also be assessed to evaluate deficits in power. For the second experiment, possible deficits in
voluntary activation of key extrinsic finger muscles will be examined through twitch interpolation and central
activation ratio techniques. Surface electrical stimulation will be superimposed on the voluntary activation of
specified finger muscles to produce maximum isometric finger force. Activation values for the paretic hand will
be compared with those of the non-paretic hand and the values measured in typically developing children. These
experimental data will be used to develop subject-specific neuromechanical computer models of the hand in
OpenSim. Muscle morphology, such as length and cross-sectional area, will be measured with ultrasound for
inclusion in each custom model. The computer models will be used to determine the sensitivity of fingertip
strength and control to different impairment mechanisms. Together, the results of this study will help to better
inform current and future rehabilitation techniques in children with cerebral palsy.