Functional Electric Stimulation
Acute spinal cord injury (SCI), leads to skeletal unloading, immobilization and induces rapid muscle atrophy and accelerated bone loss in the paralyzed limbs. Maintaining muscle and bone integrity would prove highly valuable for the improvement of general health and well being of individuals after a SCI. More importantly, early musculoskeletal deterioration may impair functional mobility such as independent standing or walking in the future. Functional electrical stimulation (FES) training is a rehabilitative approach that generates alternating leg extension and flexion even in individuals who are unable to stand or step independently. Studies involving FES have shown improvements in bone mineral density (BMD), muscle hypertrophy and muscle strength. Standing retraining (SRT) is a component of locomotor training (LT), an activity-based therapy that emphasizes the generation of muscle activity, and weight bearing in individuals who are unable to stand or walk independently. The beneficial effect of this multi modality approach may have an impact on present and future interventions for recovery of walking after SCI. At a time when biological interventions of neural repair of the spinal cord (i.e. spinal implants, trophic factors, anti-inhibitory proteins) are approaching reality, multi-dimensional rehabilitative strategies that trigger activity-dependent plasticity for motor output and therapies that may increase muscle mass and bone density should be developed to facilitate recovery and to prepare the body for a potential cure for SCI.
Therefore, the purpose of this study is to examine the basic neuromuscular and skeletal gains associated with SRT using FES for individuals after SCI compared to FES alone or SRT alone supporting the body weight as needed. Specifically, we wish to investigate if FES with SRT will increase the ability to stand independently without assistance from trainers. The primary variables measured before and after the intervention are muscle activity, muscle cross sectional area, muscle volume and generated potential muscle torque for hip and knee and BMD.
Over 200,000 people in the United States have SCIs and each year 10,000 new cases occur. Approximately 50 percent of participants with a SCI have incomplete motor function impairment and potentially may walk again. However the majority of individuals with SCI do not recover the ability to walk and rehabilitative strategies for standing (independently without assistance) or ambulation, beyond orthotics and assistive devices, have changed little over the past 20 years. Conventional rehabilitation for walking does not emphasize methods that can utilize more effectively those sensory or afferent inputs to the lumbosacral motor pools associated with locomotion. Conventional rehabilitation primarily focuses on stretching, strengthening above the level of the lesion, and any standing or gait performance generally plateaus with minimal improvement.
Many persons with SCI experience immobilization, associated with disuse atrophy of bone and muscle that probably occurs to a greater or lesser degree, correlated to the severity of bone unweighting. With the loss in bone and muscle there are often secondary complications: skeletal fragility, potential fracture risk during transferring, bending or minor falls. Often, these fractures occur without trauma or pain and are not immediately diagnosed. Significantly, the atrophy and lack of strength of the musculoskeletal system may further limit standing or walking ability. Understanding the neural and physiological mechanisms within the human spinal cord is essential to the development of effective generalized rehabilitation strategies in patients with neurological impairments. If the training of neural circuits of the lumbosacral spinal cord can be optimized, minimal levels of supraspinal sparing or biological interventions for neural regeneration may result in significant locomotor recovery in SCI patients.
We hypothesize that the combination of standing retraining (SRT) with FES, will increase standing independent of any assistance. The FES will increase muscle strength and bone density or at least slow the bone decrement. These muscle and bone improvements will be more evident than either FES alone or SRT alone. This is hypothesized because the combination of muscle activation using FES, provides a bending tension and SRT provides bilateral weight bearing consisting of compressive tension. An additional theory supporting this hypothesis is that SRT provides the appropriate sensory information related to standing for the lumbosacral neural networks to increase the motor unit recruitment and improve coordination of efferent patterns for standing. A more optimal neural control, an increase in muscle torque at the hip, knee, ankle promote an improved motor control for the functional outcome of standing as a precursor to walking.
This project will be completed at two sites: The Human Performance and Movement Analyses Laboratory (HPMAL) at KMRREC (the grant PI site) and the Human Locomotion Research Center at Frazier Rehab Institute and University of Louisville, Louisville, Kentucky. Researchers in the HPMAL at KMRREC, in collaboration with Dr Susan Harkema University of Louisville have been engaged in clinical research involving LT as rehabilitative modality since 2002. These researchers have data to suggest that LT can improve: neural activation patterns, muscle mass and locomotor capacity on the treadmill and functional outcome overground when compared to traditional therapy. In addition, our preliminary data on BMD suggests that LT with repetitive loading will decrease the decrement in BMD when compared to traditional therapy without any loading. Also, individual’s with chronic motor complete SCI (ASIA B) have muscle activation patterns on the treadmill that are highly similar to able bodied individuals walking on the treadmill but these individuals were not able to ambulate overground. We suggest that with an increase input to the neuromusculoskeletal system through SRT and FES, there may be improvement in walking.