1996 Project Reports | Home | Contents | Previous | Next |
David A. Brown, PhD, PT; Steven A. Kautz, PhD; Charles G. Burgar, MD; Cheryl D. Pierson-Carey, MS PT; Christine A. Dairaghi, BS
Problem Statement - The incidence of stroke has recently been estimated to be about 550,000 in the United States. In 1989, the number of stroke survivors in the United States approached nearly 3 million In addition, the incidence of stroke doubles with every decade after 55 years of age. Since the incidence of stroke increases with age, and as modern medicine becomes more successful at preventing mortality during a stroke, the burden of care will increase as the population ages. Along with prevention, health care goals must also include reduction of the burden of care by improving functional rehabilitation.
Objective - We have initiated and are executing a series of projects aimed at identifying major motor control impairments responsible for functional locomotor deficits that are commonly observed in persons with hemiplegia following a stroke In addition, we have initiated a project aimed at using this diagnostic information for the purpose of developing innovative and efficacious therapy tools to restore functional ambulation.
Approach - The movement task of pedaling a bicycle ergometer is used as a paradigm for measuring and treating motor control impairments associated with ambulation deficits. We choose to use pedaling because it is a dynamic, bilateral task which has many similarities to walking, but is safer and can be performed when a person is in various stages of motor recovery. In addition, pedaling is a simple, constrained motion, thus its biomechanics are much easier to measure and analyze than those of walking.
 Figure 1. Schematic drawing depicting typical experimental setup for bicycle ergometer experiments including measurement of pedal forces, crank and pedal angular rotations, and electromyographic measurements of muscle activity. In certain cases, visual feedback of select signals are supplied. |
Abnormal muscle activity patterns during pedaling
Brown, Kautz, Dairaghi
Studies in persons with post-stroke hemiplegia have investigated pathological mechanisms of muscle activity such as hyperactive stretch reflexes, improper muscle timing, and/or prolonged muscle activity, all thought to interfere with the execution of movement. This study investigated the timing and amplitudes of EMG activity in seven muscle groups as 15 subjects with hemiplegia and 12 healthy, elderly control subjects pedaled a modified bicycle ergometer at a constant velocity (40 rpm) and constant workload (120J).
When compared to control subjects, subjects with hemiplegia, on average, demonstrated significant differences in timing of muscle activity so that muscles normally on during the power phase (soleus and vastus medialis) showed prolonged muscle activity and those muscles on during transition phases (medial gastrocnemius, rectus femoris, semimembranosus, and biceps femoris) showed premature onsets. Results indicate that locomotive movement deficits are caused by a combination of pathological mechanisms related to the biomechanical function of the muscle.
Effects of exertion on motor performance during pedaling
Brown, Kautz, and Dairaghi
Controversy surrounds the once-widely accepted theory that undue exertion during exercise should be avoided because it may exacerbate impaired motor performance in spastic hemiplegia. We hypothesized that the motor performance measured during pedaling in hemiplegia is related to the level of exertion associated with workload and speed.
We examined specific measures of motor performance during pedaling for a relatively homogeneous population of hemiplegic stroke patients and compared these with a group of age-matched, neurologically-normal individuals. We measured pedal force output and EMG activity in seven muscles at combinations of five workloads (0, 40, 80, 120, and 160 Joules) and three speeds (25, 40, and 55 rpm).
Results demonstrated that stroke patients responded to increased workloads by increasing the force output of both the plegic and the non-plegic limbs without increasing the amount of negative work done by joint torques. This result is also accompanied by increased EMG activity in the power generating muscles of both limbs. Interestingly, subjects with poor motor recovery showed better motor performance at lower speeds. We conclude that, during hemiplegic exercise, challenging workloads can enhance motor output without impairing motor performance. However, exercise at challenging movement speeds should be approached with caution.
Effects of bracing on ankle muscle activity during pedaling in post-stroke hemiplegia Dairaghi, Brown, Pierson-Carey The physical therapist is continually challenged to further their hemiplegic patient's functional mobility and independence. One common method for increasing functional mobility is to brace the affected ankle. Because of the large number of individuals who are prescribed some type of ankle brace, we are proposing to quantify the pedal force and ankle muscle activity differences during pedaling associated with ankle bracing to determine if improved motor performance is observed. Twelve subjects with hemiplegia will be recruited and instructed to pedal a bicycle ergometer at a moderate cadence of 50 rpm against a workload of 80 Joules while given visual cadence feedback under five separate conditions (initially both ankles free, only affected ankle braced, only unaffected ankle braced, both ankles braced, and finally both ankles free). EMG will be measured using surface electrodes in the soleus, tibialis anterior, and medial gastrocnemius muscles of both legs. We are principally interested in the relative inter-limb force output and EMG activity produced by the affected and unaffected legs during each of the five test conditions. This research attempts to provide physical therapists with sound, scientific rationale for choosing specific exercise modalities in the rehabilitation of persons with hemiplegia.
Graded weight-bearing for improving ambulation
Brown, Burgar, Kautz, Dairaghi
We have modified a bicycle ergometer to allow the study of graded weight-bearing pedaling in individuals with impaired lower limb function. The graded weight-bearing system consists of a backboard that provides a backrest for the subject as they are tilted into different body orientations. Since the subjects are not seated, this backrest allows the subject to exercise the lower limbs at graded levels of force output by changing the amount of body weight supported through contact between the foot and pedal surface. Therefore, at the most horizontal position the subject is bearing minimal weight while exercising. At the most vertical position, the subject s bearing maximal weight. We have performed preliminary studies of the efficacy of the graded weight-bearing pedaling regime on a small group (N=8) of hemiplegic subjects. Each subject underwent a 12 week training regime. At the end of the training period, all eight subjects were able to pedal at steeper tilt angles than they had been able to originally, indicating an increased ability to support more weight. Three subjects who underwent the training regime were also given a battery of 10 lower limb motility tests before and after the training period. All three subjects showed substantial improvement in at least seven of the ten tests. The large improvements are a clear demonstration of the potential functional gains that can be achieved using graded weight-bearing pedaling.
Republished from the 1996 Rehabilitation R&D Center Progress Report.