Science has perfected the answer to calming a crying baby: hold them and walk with them for five minutes.

The evidence-based soothing strategy was derived from experiments carried out in Japan and Italy, which were analysed and published in the journal Current Biology.

The paper's authors said they hoped the finding could benefit stressed parents.

"I have raised four children," Kumi Kuroda, senior author of the RIKEN Center for Brain Science in Japan, said in a video statement. "But even I couldn't foresee the key results of this study until the statistical data came up."

The team had previously studied the "transport response" in mammals that give birth to young that are unable to care for themselves, such as mice, dogs, monkeys and humans.

When these animals pick up their babies and start walking, the young become quiet and docile, and their heart rates slow.

Dr Kuroda and colleagues wanted to explore this further in humans, and to compare the effect against other comforting behaviours, such as rocking in one spot.

They recruited 21 mother-baby pairs, with the babies being up to seven months old, and tested them under four conditions: carrying while moving, held still by their sitting mothers, lying in a still crib, or lying in a rocking cot.

Crying decreased and heart rates slowed within 30 seconds when infants were transported. There was a similar effect when they were rocked, but not when they were held motionless.

This suggested that, contrary to assumptions, being held by their mothers was insufficient to calm a child, and the transport response was an important factor.

They found that 46% of the babies fell asleep after being carried for five minutes, and an additional 18% fell asleep in the minute after.

This showed that not only did carrying stop crying, it also promoted sleep.

But they also noticed that when infants were put to bed, more than one-third became alert within 20 seconds.

Electrocardiogram readings showed the baby's heart rate rose the second they were detached from their mother's body.

However, when the babies were asleep for a longer period of time before being put down, they were less likely to awaken.

Dr Kuroda said she found this surprising, as she had assumed other factors like the way they were placed in bed or their posture would play a role, but this was not the case.

"Our intuition is very limited, that is why we need science," she said.

The researchers recommended a protocol for soothing and promoting sleep: hold and walk the baby five minutes, then sit and hold them for another five to eight minutes, before putting them to sleep.

This provides immediate comfort, unlike other methods like letting a baby cry themselves to sleep, but more work will be needed to understand if it can "train" infant sleep in the long term.