Breast milk composition after exercise of different intensities.

The purpose of this study was to determine if breast milk composition changed significantly following exercise conducted at different intensities. Nine postpartum women exercised on a treadmill up to maximal oxygen uptake (100% of VO2max) on the first laboratory visit, for 30 minutes on two subsequent occasions (50% and 75% of VO2max) and also performed a nonexercise control session. Blood and breast milk were collected prior to exercise, immediately after exercise, and at 30, 60, and 90 minutes postexercise. Blood samples were analyzed for lactic acid (LA) while milk samples were analyzed for LA, pH, lipid, ammonium, and urea. Milk LA after the 100% intensity session was significantly elevated through 90 minutes postexercise, while there was no significant increase in milk LA at any collection time after the 50% or 75% intensity sessions. There were no significant differences in milk pH, lipid, ammonium, or urea measurements after any of the exercise sessions. These data show that unlike maximum intensity exercise, moderate intensity exercise does not increase breast milk LA content.