A group of 73 male and 73 female industrial workers was studied to develop a model of maximum acceptable load of lifting (MAL) based on physical factors. Task conditions included six lifting ranges (floor to knuckle, floor to shoulder, floor to reach, knuckle to shoulder, knuckle to reach, and shoulder to reach), four lifting frequencies (two, four, six, or eight lifts per minute), and three box sizes. A factor score based model for predicting a subject's MAL was developed based on 100 subjects, and the model was validated on the remaining 46 subjects. The model consisted of two factors that accounted for 85 percent of the experimental variance: the strength factor, which consisted of shoulder, arm, standing back, leg, and composite strength; and the anthropometric factor, including body weight and abdominal depth. MAL was found to change when different muscle groups were involved, with the greatest MAL for floor to knuckle lifting and the least for shoulder to reach lifting. MAL was also found to decrease with increasing lift frequency. The authors conclude that the model is superior to previously developed models, but they caution that it can only be used to predict lifting capacity within the range of conditions studied.