A person whose hand function has been affected by a stroke can release an object more quickly when the affected arm is supported on a platform, but the support does not make it easier to grip the object, according to a new study. The study also found that active muscle-stretching exercises improved how quickly the stroke survivor could grip an object, but made release of the object more difficult. These findings show how a stroke affects hand function, and provide a roadmap for rehabilitation.
Stroke is a leading cause of long-term disability among American adults. People who have suffered strokes often experience hand impairment, including significant delays in how long it takes to grip and release objects. This study included 10 people who had hand impairments from a severe stroke that had injured one hemisphere of the brain but not the other.
In this study, the authors wanted to quantify the time needed to:
They also wanted to determine the effect that:
The study included 10 people with severe hand impairment because of a stroke. The study also included five healthy people as controls.
The study participants sat in front of a cylinder that they gripped as quickly and as strongly as they could when they heard an auditory signal. The researchers instructed them to release the cylinder as quickly as they could when the signal stopped. The researchers recorded grip initiation and release by using an electromyogram, which detects muscle activity.
The study found that the speed of grip and release was impaired in both hands for those who suffered a stroke, even though only one hemisphere of the brain had been injured. They found that:
Stroke survivors could grip the cylinder much more quickly than they could release it. The paretic hand took 1.9 seconds to grip the cylinder but required 5 seconds to release it. In comparison, the healthy controls took 0.2 seconds to grip and 0.4 seconds to release.
The study also found that the non-paretic hands of the stroke survivors had been affected, although not nearly as much as the paretic hand. The non-paretic hand took 0.5 seconds to grip and 1.6 seconds to release.
The researchers also looked at grip initiation and grip termination when the stroke survivors used a device that supported the arm on a platform, leaving the hand free. They found that the device helped stroke survivors release the cylinder more quickly. With the device, they were able to reduce the delay in grip termination by 37%. The device made no significant difference in the time needed to initiate the grip.
The assistive device compensates for gravitational forces, thereby supporting the weight of the arm and permitting relaxation of the muscles of the arm and shoulder. This allows the stroke survivor to more easily control the muscles of the fingers, wrist and hand, Dr. Seo said. She also noted that a special device may not be necessary. Supporting the paretic arm with the non-paretic arm, or using a table to support the arm, may do just as well.
The researchers also tested grip and release following 30 minutes of hand, wrist and finger muscle stretching exercises. They found the muscle stretch exercises helped stroke survivors grip the cylinder more quickly, but it further delayed time to release. The stretches reduced delay in grip initiation by the paretic hand by 32% but increased delay in grip termination by 24%.
The researchers hypothesize that the exercises activate muscles, making it easier to grip but more difficult to relax the muscles, which makes it harder to release. The stroke survivors performed the grip-and-release trials shortly after the muscle-stretching exercises. It is possible that the negative effect on release could be reduced if there was a greater time interval between the stretching and the grip and release task, Dr. Seo said. She recommends further research on this question.
In addition, according to Dr. Seo, these therapies may help improve hand function:
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