| Abstract: | A laboratory study was conducted to determine one-handed dynamic and static pulling strengths of 50 males and 49 females from 14 to 71 years of age. The dynamic strength for a 11m pull was measured to simulate the act of starting a lawn mower engine for four different starting-rope handle locations: on the engine, in the middle, on the right and on the left side of the frame. The last three were located at the back of the lawn mower at a vertical height of 63 cm from the floor and the handle on the engine was located at 42 cm. Static strength was measured for the handle in the middle. Ratings of perceived exertion were recorded for different body parts. Peak and average dynamic pulling strengths were 55% and 34% of static pulling strengths. Dynamic pulling strengths were highly correlated with peak velocity (r = 0·84). Men in the age group 21-34 years had the highest strength and women in the age group 51-71 years the least strength. Dynamic pulling strengths for women were 62% of strengths for men. Women took 10% longer to pull, had a lower peak velocity (16%), reached peak force faster (17%) and took a longer time (6%) to reach peak velocity than men. The starting handle located on the engine resulted in the maximum pulling strength and on the left side in the minimum strength. However, two out of three subjects preferred the handle either on the right side or in the middle. Fifty-five percent of the subjects indicated they would prefer a height higher than 63 cm. Maximum stresses were perceived on the shoulder and upper arm with a mean rating between fairly light and somewhat hard. Graphs of cumulative frequency distributions of average and peak dynamic pulling strengths are presented to aid in the determining forces required to start a lawn mower engine in order to satisfy a desired percentage of the population. |
