The Impact of Shoulder Abduction Loading on Volitional Hand Opening and Grasping in Chronic Hemiparetic Stroke.
Yiyun Lan, Jun Yao, Julius P A Dewald
PMID 28506146WHAT IT FOUND
Lifting the affected arm against gravity worsened hand opening in moderate chronic stroke and made severely impaired participants close their hand instead of opening it.
Controls were unaffected. Total maximal grasping force did not change, but involuntary grasping force rose with loading.
Key findings
01In individuals with moderate chronic stroke, the area formed by the thumb and fingertips during maximal hand opening decreased as shoulder abduction loading increased. Controls did not show this decrease.
02Severely impaired stroke participants did not open the hand. They generated grasping forces when asked to open, and these forces were greater at 50% loading than at 25% loading or table support.
03Shoulder abduction loading increased involuntary synergy-induced grasping forces in both stroke groups, but total grasping forces did not differ significantly between loading conditions or groups.
STILL TO COME
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What it does not show
The study included 36 individuals, so the sample was small. One participant in the severe group and three participants in the moderate group were excluded from hand opening analysis because thumb position could not be tracked. One participant in the severe group and two participants in the moderate group were excluded from grasping force analysis because thumb force measurement was difficult. Participants had to lift against gravity and generate elbow extension, so results may not apply to more impaired patients who cannot do that. The arm was supported in a chair and fingers on a cylinder. This setup may differ from daily reaching tasks. The study did not test a treatment, so it cannot tell therapists whether changing shoulder loading improves function. The severe group did not produce hand pentagon area, so the hand opening result applies mainly to the moderate group. Total grasping forces were not different, so the finding is about involuntary synergy and hand opening, not maximal grasp strength.
The easy way to misread this
Do not conclude that lifting the arm reduces total maximal grasp strength. The total grasping forces did not differ significantly between loading conditions or groups. The change was in hand opening and in involuntary synergy-induced grasping force.