To quantify spinal stress biomechanical models are often used. Static models reveal the postural effects due to gravity, while dynamic models also take into account inertial factors. We used both dynamic and static models to evaluate the lumbosacral compression when 20 subjects lifted a box weighing 15 kg from a 10 cm high shelf to knuckle height with four lifting techniques. The mean peak acceleration of the load was 4·9 − 6·3ms−2, thus increasing the force at the hands by over 50%. The static peak compression was 3989−4650 N and the dynamic 5866−6629 N, the increase due to inertial factors being 33−60% depending on lifting technique.