Latest research reveals that 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.

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.

In this study, the authors wanted to quantify the time needed to grip an object with the hand directly affected by the stroke (the paretic hand) and the non-paretic hand (the unaffected hand controlled by the uninjured hemisphere) and release an object with both the paretic and non-paretic hands. They also wanted to determine the effect that a device that supports the arm has on grip and release times, and stretching exercises for the hand and finger muscles has on grip and release times.

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.

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.

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 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.

The study, “Delays in grip initiation and termination in persons with stroke: Effects of arm support and active muscle stretch exercise” appears in the online edition of the Journal of Neurophysiology. The authors are Na Jin Seo, William Z. Rymer and Derek G. Kamper, of the Rehabilitation Institute of Chicago. Rymer is also affiliated with Northwestern University, and Kamper with the Illinois Institute of Chicago.
   
[Source: American Physiological Society]