Scientists looking at groups of people lifting heavy boxes saw subtle differences between men and women that could increase women’s risk for chronic back problems, according to a study published online in the journal Applied Ergonomics.

Ann Lukits, a writer for the New York Times recently wrote about the study. Here’s what she had to say…..

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 on 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 6 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 5 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 at the back during the initial phase 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.

All of the men, but none of the women, moved their joints in a synchronous pattern during the actual lift, which is more protective of the back. The researchers said this tendency was probably due to their greater strength.

But women held the boxes significantly closer to their body, a safer lifting strategy.

* Some workers may have altered their usual lifting technique in the laboratory setting, the researchers said. Age, work experience and previous injuries may have contributed to lifting differences among workers, they said.    7/28/14

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