Lactate Concentrations in Breast Milk Following Maximal Exercise and a Typical Workout

Abstract

Past studies have demonstrated significant increases in the concentration of lactate in breast milk following exercise and that infants prefer ingesting the preexercise milk to the postexercise milk. Both of these studies used maximal exercise for the exercise stimulus. However, most women do not exercise to maximal capacity during a typical workout. The lactate accumulation in breast milk following a typical workout is unknown. Thus, the purpose of this study was to compare the concentration of lactate in breast milk following a typical workout (WORK) to maximal exercise (MAX). Subjects (n = 23 lactating women) performed a maximal graded exercise test (Vo2max = 36.3 ± 9.0 mL·min−1kg−1) and conducted their typical workout in the laboratory or in the dance studio. The intensity of the WORK (55.1 ± 18.3% of heart rate reserve) was estimated (via Karvonen method) from rest, exercise, and maximal heart rates. For both WORK and MAX, milk was collected at rest preexercise and 10 min postexercise and was analyzed for the concentration of lactate. A significant increase in lactate was found in the milk following WORK (pre = 0.61 ± 0.14 mM; post = 1.06 ± 0.33 mM) and following MAX (pre = 0.63 ± 0.18 mM; post = 2.88 ± 0.80 mM). In addition, a significant difference in postexercise lactate concentrations was found between MAX and WORK. These results form the basis for further study of the workout factors that affect lactate accumulation in breast milk so that more specific guidelines can be formulated for lactating women experiencing nursing problems after exercise.