February 2010

In the Moment: Neuromuscular

by Jordana Bieze Foster

CP: Means sap strength data

Subgroup analysis may be key to gait link

Gait researchers’ frustrations in demonstrating benefits of strength training in children with cerebral palsy can be traced to the heterogeneity of the study population, according to a National Institutes of Health study that offers some insight as to which patients are most likely respond.

NIH researchers assessed the gait kinematics of eight children with spastic diplegia and a crouched internal rotation gait pattern, before and after eight weeks of progressive resistance exercise targeting the hip and knee extensor muscles. The children exercised for one hour per session, three times a week, using a combination of open- and closed-chain exercises designed to have the greatest effect near terminal extension.

The pilot trial, published in the December issue of Physical Therapy, did not demonstrate any significant effect of strength training on gait for the study group as a whole. But further analysis shed light on factors that may predispose a child to a better outcome.

The three subjects who could ambulate independently demonstrated a small improvement in their crouch gait (less knee flexion) after the intervention, whereas all but one of the five who used assistive devices walked with a more pronounced crouch after strength training. The authors theorized that the more functional children were most likely to respond because of lower levels of spasticity and fewer motor control deficits that could interfere with activation of muscles even if they had become stronger.

Hamstring spasticity in particular could be an issue. The same exercises that were designed to strengthen the quadriceps could also have strengthened the hamstrings, which could explain the  decreased knee extension seen in subjects with hamstring spasticity. A detailed analysis of the one subject who responded positively to the training program revealed that although he walked with excessive knee flexion, his hamstring muscles were not excessively tight. After the intervention, that subject experienced substantial increases in knee extensor and hip extensor strength, accompanied by decreased knee flexion, hip flexion and hip internal rotation.

Overall, however, the authors concluded that the variability of neuromuscular impairments in children with CP make it difficult to predict how a group will respond to strength training, and suggested that such heterogeneity may be responsible for the inconsistent findings of previous studies in which outcome measures were reported as group averages. A June 2009 meta-analysis  published in the Australian Journal of Physiotherapy found that strengthening interventions did not improve strength or walking speed, and increased Gross Motor Function Measure score to such a small degree that the improvement, though statistically significant, was not clinically significant.

Another recent study, however, suggests that gait in children with CP could potentially be improved using an approach that typically is used specifically for upper-extremity rehabilitation.

Modified constraint-induced movement therapy (mCIMT) is a neuromuscular rehabilitation technique in which patients are forced to use their affected limb when their unaffected limb is restrained (for example, by putting a mitten on the unaffected hand to improve manual dexterity in the affected hand). A similar approach has been used in patients with lower extremity hemiplegia, by constraining the unaffected leg, but this technique has practical limitations.

Researchers from the Medical University of South Carolina, however, theorized that because the motor learning involved in mCIMT has been shown to involve neural reorganization at the cortical level, upper extremity mCIMT could have an effect on the lower extremities as well. They analyzed 12 preschool children with hemiplegic CP who underwent mCIMT for five consecutive days, six hours per day. Gait analysis revealed a significant increase in heel to heel base of support following the intervention, as well as nonsignificant improvements in other gait variables. The findings were published in January in Disability & Rehabilitation.

Treadmill outperforms outdoor walking for stroke rehabilitation

There are plenty of advantages to exercising outdoors, but research from Norway suggests that treadmill walking may actually be more effective for improving spatial and temporal gait characteristics in chronic stroke patients.

Investigators from Sunnaas Rehabilitation Hospital in Oslo randomized 39 stroke patients to one of two walking exercise interventions, either outdoors at a self-selected speed or indoors on a treadmill at a mean of 0.5 m/s. The intervention lasted for as long as the patients’ stay at the rehabilitation center, a mean of 2.5 weeks in each group. The sessions differed in length, however, at a mean of 12 minutes for treadmill walking (107 minutes total) and 29 minutes for outdoor walking (316 minutes total).

Despite spending significantly less time exercising, patients in the treadmill group significantly outperformed the outdoor walkers at the end of the intervention with regard to six minute walk test speed and distance, 10-meter walking speed, bilateral stride length, and step width. Cadence did not differ significantly between the groups.

The findings were published in the January issue of Clinical Rehabilitation.

Ankle weakness, not instability, explains reduced speed after TBI

Although increased lateral movement of the center of mass is associated with traumatic brain injury, an Australian study reports that decreased gait speed in TBI patients is actually related to reduced ankle power rather than postural instability.

Researchers from the University of Melbourne analyzed treadmill walking in 55 patients with TBI and 10 healthy controls.

When the groups were matched for speed (self-selected by the TBI patients), those in the TBI group demonstrated significantly reduced ankle power generation at push off and increased hip power generation at early stance and pre-swing compared to the controls. When walking at faster speeds, hip power generation increased to a greater degree in the TBI patients than the controls, likely in compensation for the lack of ankle power.

The TBI patients also exhibited significantly increased width of the base of support and postural instability at the matched speed; however, when walking at faster speeds, postural stability was not affected in either group.

The findings were e-published on January 19 by Neurorehabilitation and Neural Repair.

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