TOOL DESIGN, USER CHARACTERISTICS AND PERFORMANCE - A CASE-STUDY ON PLATE-SHEARS

Performance, grip forces and fatigue were studied in six male and six female subjects while cutting with plate-shears. Three types of plate- shears were used, one standard and two modified, either with a spring grip, or with a spring grip in combination with a reduced grip span. I n addition, three types of plate - easy, moderately difficult and diff icult to cut - were used. Male subjects used around 40% of their maxim al grip force and female subjects around 60% with the moderately diffi cult plate; the male subjects produced more than twice as long a cutti ng distance as the females. Neither EMG analysis (frequency shifts) no r subjective exertion or reduction of handgrip MVC indicated a more pr onounced fatigue in women than in men, probably because the female sub jects used about a 50% lower cutting rate than the men. Productivity ( in cm cut per min) was strongly related to measures of hand size and t o the relative grip force used. Thus in a multiple regression analysis using metacarpal hand circumference and relative grip force as indepe ndant variables, R2 was 0.77. The two types of modified plate-shears w ere preferred by all and gave a roughly 30% higher productivity in the male subjects but did not improve productivity in the females. Howeve r, with a spring grip and reduced grip span, the female subjects reduc ed the relative grip force used from around 65 to 50%. The total work (force-time integral) per cm cut was not influenced by type of plate-s hear.