Objective: The present study examined the influence of workplace manual labor on measures of muscular fitness, with a secondary aim to investigate the relationship between muscular fitness and work performance in blue-collar (BC) workers. Methods: Leg extension isokinetic strength at slow and fast velocities, hamstring and hip-flexor flexibility, and low back muscular endurance were examined in young and older BC workers and white-collar (WC) controls, while work performance was examined in the BC cohort. Results: There were no differences in muscular fitness variables between BC and WC groups; however, the older men had lower low back muscular endurance (−43.0%) and strength at slow (−9.4%) and fast (−12.7%) velocities. Work performance was associated with strength at fast velocities (r = 0.633) in the older BC workers. Conclusions: Leg strength may influence work performance, with higher velocities becoming more important in older workers.