Feeding method and motor activity in 3-month-old human infants.

It is currently acknowledged that breast-fed and formula-fed infants exhibit different rates of physical growth. Little is known, however, about behavioral differences that may be attributable to early feeding method. In the present investigation, activity level in 3-mo.-old infants was examined by measuring motoric output in 40 breast-fed and 40 formula-fed infants. Maternal ratings of temperament did not differ across the two groups, but scores derived from the actometer in a laboratory setting showed breast-fed infants to be more active. Upper limb activity appeared to be particularly sensitive to feeding regimen. Possible explanations for this effect as well as implications of these results are discussed.