The Mechanics of Carrying a Baby

 

With a right leg slightly shorter than the left, the left hip is elevated over the right creating a tilt across the pelvis. The foundation of the spine at the Sacrum leans to the right encouraging mild scoliosis with right convexity. With the spine and upper torso being offset to the right of centre, weight distribution is too. The hips shift to the left counter balancing this weight shift. Hence, the elevated and laterally projecting left hip becomes the perfect perch for baby. We hardly have to think about it, left arm casually draped about baby secure on the left hip. It is only with difficulty we carry baby on the right hip.

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If you have not experienced this, find a small child and try it out. We all have a short right leg. Even or near even leg length is rare. In ten years I have sighted only one naturally short left legged individual. She is a young mother who carries her babies on the right hip.

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Evolutionary adaptation of a structurally short right leg in Homo Sapiens was influenced by the fact we have a dominant right hand. Freeing the strong right hand for work and defence increased the chance of survival for mother and child in prehistoric times. We carry baby on the left hip. It is the most successful model.

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Above explanation is simplified. A complexity is the fact that frequently the hip/ilium of the longer leg rotates anteriorly in the Sagittal plane to pull up the longer leg, functionally shortening leg length, reducing pelvic tilt, protecting the spine to some degree and making us feel more comfortable. This is the First Cardinal Sign of Short Right Leg Syndrome. This seems counter to the original intention of tilting the pelvis and generating the lateral shift of the left hip for baby carrying purposes. However, hip rotation does not totally eliminate right leaning pelvic tilt and subsequent mild scoliosis with right convexity through the lumbar spine and, in most cases, through the thoracic too. This is sufficient to initiate the lateral shift of the pelvis and introduces another functional adjustment elevating the left hip and dropping the right hip. Said in another way, geometrically, if two long lines (legs) joined at the top by a short bar (pelvis) anchored on flat ground sway laterally, the ipsi-lateral juncture (left hip) elevates and contra-lateral juncture (right hip) descends. For practical baby carrying purposes, it might be more about the lateral shift than elevation that creates the perch on which to carry baby. The tilted pelvis apart from shifting the centre of weight, adds a stability factor to the lower limbs driving up through the right leg. We lean into things to hold them.