A pregnant woman's spine is her flexible friend
A pregnant woman's lower spine has a hidden flexibility which shifts her centre of gravity backwards so she does not topple forwards due to the weight of her baby, researchers have found.
An analysis of the female backbone has shown how the spinal curvature of a woman becomes more pronounced when pregnant. This ensures the weight of the developing foetus is placed directly over the pelvis and reduces pain and fatigue for the woman's back muscles.
The same researchers have shown that the male spine does not have the same features and so is inherently more rigid.
This suggests the flexibility of the female spine has come about because of the extra strains put on the upright posture during pregnancy, scientists said.
"Pregnancy presents an enormous challenge for the female body. It must change in dramatic ways to accommodate the baby, and these changes affect a woman's stability and posture," said Katherine Whitcome of Harvard University.
"Enhanced curvature and reinforcement of the lower spine are key to maintaining normal activities during pregnancy," Dr Whitcome added.
It is the first time anyone has demonstrated a difference between the sexes in the vertebrae of the human lumbar region the lower back according to the scientists, whose study is published in the journal Nature.
Dr Whitcome said the natural curvature of the lower back, which is known as lordosis, stabilises the upper body above the lower body.
This is especially important during pregnancy because of the need to shift the centre of gravity backwards to compensate for the extra weight at the front.
The study analysed the posture of 19 pregnant women. When standing, the women leaned back slightly to increase their lordosis by as much as 60 per cent by the time they were about to give birth.
Dr Whitcome said: "In females, the lordosis is subtly different than that of males, because the curvature extends across three vertebrae, while the male lordosis curves across only two vertebrae.
"Loading across three vertebrae allows an expectant mother to increase her lordosis, realigning her centre of gravity above her hips and offsetting the destabilising weight of the baby."
In addition to being able to curve the spine more during pregnancy, the joints in the vertebrae of women are relatively larger than in men and flare out further down the spine, which improves the strength of the lower spine allowing women to lean back further. Lisa Shapiro, an anthropologist at the University of Texas at Austin, said female chimpanzees do not show this adaptation while the spine of a female Australopithecus a two-million-year-old primate which walked on its feet and had human characteristics does show the change. "Natural selection favoured this adaptation because it reduces extra stress on a pregnant female's spine," Dr Shapiro said.
"Without the adaptation, pregnancy would have placed a heavier burden on back muscles, causing considerable pain and fatigue and possibly limiting foraging capacity and the ability to escape from predators," she said.
"Any mother can attest to the awkwardness of standing and walking while balancing pregnancy weight in front of the body. Yet our research shows their spines have evolved to make pregnancy safer and less painful than it might have been if these adaptations had not occurred."
Sales of the tablet are set to fall again, say analysts
Met Police confirm that there was a 'minor disturbance'
Trend which requires crisps, a fork and a strong stomach is sweeping Mexico's streets
George Lucas criticises the major Hollywood film studios
Does Chris Grayling realise what a vague concept he is dealing with?
Parties threaten resort's image as a family destination
I Am Bread could actually be a challenging and nuanced title
- 1 Jack the Ripper: Scientist who claims to have identified notorious killer has 'made serious DNA error'
- 2 Banksy arrest hoax: Internet duped by fake report claiming that the street artist's identity has been revealed
- 3 Are you ready for Crazy Doritos, the red-hot snack food craze sweeping Mexico’s streets?
- 4 Drink alcohol and eat meat to improve male fertility - but cut down on coffee, studies suggest
- 5 Brian Harvey turns up at Downing Street and 'demands to speak to Prime Minister'
Isis in Kobani: US resupplies Kurdish fighters by plane - then Turkey allows reinforcements through its border
Jack the Ripper: Scientist who claims to have identified notorious killer has 'made serious DNA error'
Banksy arrest hoax: Internet duped by fake report claiming that the street artist's identity has been revealed
Super-sized ships arrive in Britain: How big can they get?
Brian Harvey turns up at Downing Street and 'demands to speak to Prime Minister'
Cameron is warned 'no possibility' of UK reducing immigration and that bid to bring in quota on migrant workers would be illegal
Residents should throw a street party and mix with immigrant neighbours, councils told
London bus driver 'kicks gay couple off for kissing'
Russell Brand threatened with arrest after filming outside Fox News headquarters
Amal Alamuddin calls for the return of the Elgin Marbles from Britain: 'Injustice has persisted for too long'
Lord Freud: Tory welfare minister apologises after saying disabled people are 'not worth’ the minimum wage
£21500 - £40000 per annum: Randstad Education Plymouth: ***KS1 & KS2 Teachers ...
£80 - £140 per day: Randstad Education Leeds: Year 5 Teacher KS2 teaching job...
£35000 - £45000 Per Annum Pensions Scheme After 6 Months: Clearwater People So...
£35000 - £37000 per annum + Benefits: Ashdown Group: Systems Analyst / Busines...