The Chartered Society of Physiotherapists (CSP) says should take potential stresses and strains on the spine into account when designing new trolleys.

And physiotherapist Alison Middleditch, who writes textbooks on the treatment of back pain, said large, unsteerable trolleys were causing chronic problems.

She said: "I saw three women last week who had suffered damage to their lower and upper backs after twisting round to control and steer their trolleys, and bending over to unpack and pack their goods."

She added: "The constant twisting and bending places strains on the spine and can lead to damage to the ligaments and discs.

"We have definitely seen an increase in these problems, especially among women, who do most of the shopping."

She claimed poor design was at the root of the problem.

A spokesman for CSP encouraged the public to be more aware of their backs when pushing and unloading trolleys.

'New trolleys are better'

In response, supermarket giant Asda said it was doing its best.

A spokesman said: "We have taken everything into account to ensure that it is as ergonomically friendly as possible - including the depth and width.

"Our customers were also involved in the design and testing stages."

More than 300,000 working days are lost every year due to back pain - it is thought this costs the economy �1.3bn.