By ANN LUKITS
Scientists observing groups of people lift heavy boxes found subtle differences between the sexes that could increase women’s risk for chronic back problems, according to a study published online in the journal Applied Ergonomics.
One important difference was the way men and women coordinated their joint movements—including knee, hip and lower back—when lifting an object from a low height. Women tended to move each joint separately, one after the other, which put most of the stress on the lower spine, the researchers said. The men, particularly those with lifting experience, moved their joints almost in unison, which is safer for the back.
The study in Montreal observed 30 men and 15 women, ages 25 to 41 years old, employed in manual material-handling jobs that involve heavy lifting and carrying. Half of the men had an average of 15 years of experience and half had about six months’ experience. The women had been employed for an average of seven years and were significantly smaller than the men. Participants were asked to transfer 24 boxes, each weighing 33 pounds, from one wooden pallet to another and then back again, up to five times in 30 minutes. The lifting sessions were completed over a 10-day period and subjects were allowed to rest for at least a day between each one.
Special motion-camera systems recorded participants’ movements.
All the subjects moved their joints in a sequential pattern, with the knees leading the hips and the hips leading the back during the initial phases of the lift. But there was less delay between the joint motions among men, especially the experienced lifters, whose lifting strategy was closer to a squat lift, with knees bent and straight back, the recommended posture to avoid back injury. The women and novice men were more likely to use the more dangerous stoop lift—with their torso more bent and their knees less bent—than the experienced men.