This preliminary study was conducted to validate subjective perception of effort as indicator of the tolerable workload for prolonged lifting tasks. Three healthy male subjects underwent endurance and incremental lifting tests. Cardiorespiratory parameters (HR, VO2) were monitored with a portable telemetric oxygen uptake analyzer, mechanical parameters were calculated from a lift dynamometer. Rating of perceived exertion was given on Borg's CR-10 scale. Individual fitness profiles for lifting tasks were obtained from the individual relationships between oxygen consumption and heart rate at different lifting frequencies. Physiological responses to repetitive lifting were matched with subjective perceptions. The relationship between perception of exertion and time was described by power functions, Y = a.Xn, in which 0 < n < 1. A single-variable statistical regression for power functions was performed to obtain the individual "iso-perception" curves. The iso-perception curve corresponding to a "moderate effort" (CR3) identified the individual tolerable threshold for prolonged lifting tasks. The individually tolerable power output over time for lifting tasks was calculated.