Energy cost models for combined lifting and carrying tasks

Abstract

Experiments were conducted on ten physically fit male subjects (age group—24.1 ± 3.35 years, body weight—78.43 ± 5.77 kg) to determine their metabolic responses to combined manual materials handling tasks, viz., lifting and carrying. A setup using a modified treadmill was employed to simulate these tasks. Oxygen uptake (V o 2 , l/min) and heart rate (HR, beats/min) were the response variables, whilst a number of task related parameters: load handled, height of lift, frequency of handling, carrying distance and load width, were manipulated using a rotatable central composite design. Energy cost equations were established for combined handling tasks under two height ranges of lift, floor to a height of 150 cm and 75 cm (table height) to a height of 150 cm. The models were compared with responses for individual handling tasks and validated using the “Prediction Error Sum of Squares”. The most stressful task appeared to be the one in which a load (even as low as 13 kg) was lifted from the floor the shoulder height and then carried over distances exceeding 3 m at relatively low frequencies. It was also established that the net metabolic energy expenditure for combined tasks cannot be estimated by summing the net steady state metabolic costs for individual task components.