New mothers who are breastfeeding their babies may need more aerobic and resistance exercise in order to combat temporary bone loss caused by calcium depletion, says a recently published study from the American College of Sports Medicine.

Cheryl Lovelady, Ph.D., and her research team measured bone mineral density in 20 women four to 20 weeks postpartum and found that those who didn't exercise lost around 7 percent of their lower-spine bone density in that time period.

"During lactation, women transfer around 200 milligrams of calcium per day from their own stores to their breast milk," Lovelady said. "Calcium is critically linked to bone density and health, and this depletion can result in loss of bone mineral density. When mothers wean their infants, bone mineral density usually returns to normal levels. We proposed that weight-bearing exercise would minimize bone losses during lactation and decrease the risk of osteoporosis later in life."

Exercise - especially strength training - can slow bone loss during lactation, the study found. Women who combined strength training and aerobic exercise three days a week kept their lower-spine bone mineral density loss to just 4.8 percent - highly preferable to the 7-percent loss in the non-exercising group.

In addition, regular weight-bearing exercise has an added benefit for moms trying to shed post-pregnancy weight: the regular exercisers in the study significantly improved their body composition compared to the non-exercisers, lowering their body fat percentage and increasing lean mass, even without dietary intervention. Exercisers increased their one-repetition maximal strength anywhere from 31 to 221 percent.

"Women in our study found themselves overall healthier and stronger after completing the post-partum exercise program, which lasted just 16 weeks," Lovelady said. "Moreover, implementing this exercise into daily life can help entire families get active and improve their overall health."

More guidelines for exercise during pregnancy and postpartum can be found in the ACSM Roundtable Consensus Statement "Role of Physical Activity on Pregnancy and Postpartum."

Medicine & Science in Sports & Exercise® is the official journal of the American College of Sports Medicine, and is available from Lippincott Williams & Wilkins at 1-800-638-6423. For a complete copy of the research paper (Vol. 41, No. 10, pages 1902-1907) or to speak with a leading sports medicine expert on the topic, contact the Department of Communications and Public Information at 317-637-9200 ext. 127 or 133. Visit ACSM online at

The conclusions outlined in this news release are those of the researchers only, and should not be construed as an official statement of the American College of Sports Medicine.

American College of Sports Medicine