Augmenting Ankle Plantarflexor Function in Cerebral Palsy

The first specific aim is to quantify improvement in ankle muscle function and functional mobility following targeted ankle resistance gait training in ambulatory children with cerebral palsy (CP). The primary hypothesis for the first aim is that targeted ankle resistance training will produce larger improvements in lower-extremity motor control, gait mechanics, and clinical measures of mobility assessed four- and twelve-weeks post intervention compared to standard physical therapy and standard gait training. The second specific aim is to determine the efficacy of adaptive ankle assistance to improve capacity and performance during sustained, high-intensity, and challenging tasks in ambulatory children with CP. The primary hypothesis for the second aim is that adaptive ankle assistance will result in significantly greater capacity and performance during the six-minute-walk-test and graded treadmill and stair stepping protocols compared to walking with ankle foot orthoses and walking with just shoes.

A child's ability to walk effectively is essential to their physical health and general well-being. Unfortunately, many children with cerebral palsy (CP), the most common cause of pediatric physical disability, have difficulty walking and completing higher-intensity ambulatory tasks. This leads to children with CP engaging in levels of habitual physical activity that are well below guidelines and those of children without disabilities, which in turn contributes to many secondary conditions, including metabolic dysfunction and cardiovascular disease. There is broad clinical consensus that plantarflexor dysfunction is a primary contributor to slow, inefficient, and crouched walking patterns in CP; individuals with CP need more effective treatments and mobility aids for plantarflexor dysfunction. To meet this need, this proposal aims to evaluate a holistic strategy to address impaired mobility from plantarflexor dysfunction in CP using a lightweight, dual-mode (assistive or resistive) wearable robotic device. This strategy combines two complementary techniques: (1) targeted ankle resistance for neuromuscular gait training that provides precision therapy to elicit long-term improvements in ankle muscle function, and (2) adaptive ankle assistance to make walking easier during sustained, high-intensity, or challenging tasks. Aim 1: Quantify improvement in ankle muscle function and functional mobility following targeted ankle resistance gait training in ambulatory children with CP Approach - Repeated Measures (RM) and randomized controlled trial: The investigators will compare functional outcomes following targeted ankle resistance training (2 visits/week for 12 weeks) vs. dose-matched standard physical therapy (RM) and vs. dose-matched standard treadmill training (randomized controlled trial). Primary Hypothesis: Targeted ankle resistance training will produce larger improvements in lower-extremity motor control, gait mechanics, and clinical measures of mobility assessed four- and twelve-weeks post intervention compared to the control conditions. Aim 2: Determine the efficacy of adaptive ankle assistance to improve capacity and performance during sustained, high-intensity, and challenging tasks in ambulatory children with CP Approach - Repeated Measures: The investigators will compare task capacity and performance with adaptive ankle assistance vs. standard ankle foot orthoses and vs. shod (no ankle aid) during (a) 6-minute-walk-test, (b) extended-duration over-ground walking (sustained), (c) graded treadmill (high-intensity), and (d) stair-stepping (challenging) protocols. Task capacity and performance will be measured by duration, metabolic cost, speed, and stride length, as applicable. Primary Hypothesis: Adaptive ankle assistance will result in significantly greater capacity and performance compared to the control conditions.

We will conduct a randomized controlled trial (treatment vs. control) to compare functional outcomes following bilateral targeted ankle resistance training (2 visits/week for 12 weeks) vs. dose-matched standard functional gait training.

We will conduct a randomized controlled trial (treatment vs. control) to compare functional outcomes following bilateral targeted ankle resistance training (2 visits/week for 12 weeks) vs. dose-matched standard functional gait training.

We will use a within-subject repeated measures design to compare both gait training groups to matched standard physical therapy.

We will compare task capacity and performance with adaptive ankle assistance vs. standard ankle foot orthoses and vs. shod (no ankle aid).

We will compare task capacity and performance with adaptive ankle assistance vs. standard ankle foot orthoses and vs. shod (no ankle aid).

We will compare task capacity and performance with adaptive ankle assistance vs. standard ankle foot orthoses and vs. shod (no ankle aid).

Similarity of the plantarflexor muscle activity profile across the gait cycle, measured using surface electromyography (the measurement tool) of the soleus muscle, to the average unimpaired electromyography muscle activity profile, as calculated via cross-correlation coefficient. A higher value indicates greater similarity.

Similarity of the plantarflexor muscle activity profile across the gait cycle, measured using surface electromyography (the measurement tool) of the soleus muscle, to the average unimpaired electromyography muscle activity profile, as calculated via cross-correlation coefficient. A higher value indicates greater similarity.

Similarity of the plantarflexor muscle activity profile across the gait cycle, measured using surface electromyography (the measurement tool) of the soleus muscle, to the average unimpaired electromyography muscle activity profile, as calculated via cross-correlation coefficient. A higher value indicates greater similarity.

Distance traveled in 6 minutes during a 6-minute-walk-test protocol. A longer distance indicates greater walking capacity.

Distance traveled in 6 minutes during a 6-minute-walk-test protocol. A longer distance indicates greater walking capacity.

Distance traveled in 6 minutes during a 6-minute-walk-test protocol. A longer distance indicates greater walking capacity.

Variance in muscle activity accounted for by one muscle synergy assessed using surface electromyography (the measurement tool) of the soleus, tibialis anterior, medial hamstrings, and vastus medialis. Muscle synergies will be computed from non-negative matrix factorization. Lower variance accounted for by one muscle synergy indicates a desired greater complexity of motor control.

Variance in muscle activity accounted for by one muscle synergy assessed using surface electromyography (the measurement tool) of the soleus, tibialis anterior, medial hamstrings, and vastus medialis. Muscle synergies will be computed from non-negative matrix factorization. Lower variance accounted for by one muscle synergy indicates a desired greater complexity of motor control.

Variance in muscle activity accounted for by one muscle synergy assessed using surface electromyography (the measurement tool) of the soleus, tibialis anterior, medial hamstrings, and vastus medialis. Muscle synergies will be computed from non-negative matrix factorization. Lower variance accounted for by one muscle synergy indicates a desired greater complexity of motor control.

Stride-to-stride variability of lower-extremity muscle activity for the soleus, tibias anterior, vastus lateralis, and medial hamstrings, measured via surface electromyography and calculated as the variance ratio across strides.

Stride-to-stride variability of lower-extremity muscle activity for the soleus, tibias anterior, vastus lateralis, and medial hamstrings, measured via surface electromyography and calculated as the variance ratio across strides.

Stride-to-stride variability of lower-extremity muscle activity for the soleus, tibias anterior, vastus lateralis, and medial hamstrings, measured via surface electromyography and calculated as the variance ratio across strides.

Peak Lower-extremity joint angles summed across the ankle, knee, and hip joints, measured using motion capture (the measurement tool).

Peak Lower-extremity joint angles summed across the ankle, knee, and hip joints, measured using motion capture (the measurement tool).

Peak Lower-extremity joint angles summed across the ankle, knee, and hip joints, measured using motion capture (the measurement tool).

Gross Motor Function Measure - 66, sections (D) standing, and (E) walking, running and jumping. Higher scores are better, and range from 0-3 for each measure.

Gross Motor Function Measure - 66, sections (D) standing, and (E) walking, running and jumping. Higher scores are better, and range from 0-3 for each measure.

Gross Motor Function Measure - 66, sections (D) standing, and (E) walking, running and jumping. Higher scores are better, and range from 0-3 for each measure.

Metabolic cost estimated from a wearable indirect calorimetry system during the 6-minute-walk-test, and treadmill and stair stepper bruce protocols

Subject perceived exertion (validated pictorial pediatric exertion scale). The scale is from 1-10, where a higher number indicates more effort.

Average stance-phase plantar flexor muscle activity assessed through surface electromyography of the soleus muscle.

Inclusion Criteria: Ages between 8 and 18 years old, inclusive. Diagnosis of CP and a pathological gait pattern caused by ankle dysfunction. Able to understand and follow simple directions (based on parent report, if needed) and walk at least 30 feet with or without a walking aid (Gross Motor Function Classification System (GMFCS) Level I-III). At least 20° of passive plantar-flexion range of motion. Exclusion Criteria: Concurrent treatment other than those assigned during the study. A condition other than CP that would affect safe participation. Surgical intervention within 6 months of participation.