Inhibition of individual fingers during grip strength exertion

Abstract

(1) Individual finger strengths of maximum isometric voluntary flexion were measured separately during simultaneous flexion of several fingers. (2) Every finger exerted its maximum strength when it worked alone (unidigital condition) but exerted decreasing strength in proportion to the number of other fingers working together (multidigital condition). (3) The ratio of this decrease relative to the strength exerted under the unidigital condition (unidigital strength) was higher in the index and little fingers (30%) than in the middle and ring fingers (15–25%). (4) The cross-sectional area of flexors in the forearm measured by ultrasonic photography showed higher correlation with the sum of unidigital strengths than to the sum of individual share strengths (strengths exerted by single fingers under multidigital conditions). (5) Electrical activity decreased in accordance with the strength decrease due to the increase of co-working fingers showing that each component of finger flexor suffers inhibition. (6) ‘Efferent synergistic inhibition’ among fingers was proposed to explain this decrease in strength. (7) Individual share strength during grip strength exertion was greatest in the middle finger (33% of grip strength) followed by the ring(27–28%), index (23–25%) and little (15–16%) fingers.