A study of pulling strengths of younger and older tractor operators was conducted. The purpose of the study was to determine if older male farm tractor operators had the strength to use a wrench to operate manually adjustable rollover protective structures (ROPS) on the tractors. The study group consisted of 23 male orchardists, 21 to 70 years (yr) old, who used tractors in their work. They were divided into two groups for the study: 11 who were 56 to 70yr old (older group) and 12 who were under the age of 55yr (younger group). The subjects were evaluated on three types of functional strength tests designed to simulate the exertions required when using a wrench to tighten or loosen fasteners on an ROPS. The tests consisted of a one hand shoulder height isometric pull, a one hand overhead isometric pull, and a two hand forearm isometric lift using a mobile testing unit. The average strength shown by the younger subjects on the forearm lift, overhead pull, and shoulder height pull tests was 115.583, 137.417, and 95.500 pounds, respectively. The mean strengths shown by the older subjects on the tests expressed as a percentage of those of the younger subjects were: forearm lift 85%, overhead pull 97%, and shoulder height pull 78%. The corresponding fifth percentile strengths were 64, 89, and 81%. Age was negatively correlated with the strengths required for the various pulls, the forearm lift and shoulder height pull showing the most pronounced age effect. The authors conclude that strength among healthy males does not decrease uniformly with age for all muscle groups. A discussion of designs for manually adjustable ROPS for tractors is presented.