Daily physical activity is associated with increased sonographically measured bone status during lactation

OBJECTIVES: The purpose of this cross-sectional study was to investigate the association between daily physical activity and sonographically measured bone status among women during the lactation period. METHODS: Final participants were 152 women 4 months after childbirth. Bone status of the participants was measured using quantitative ultrasonometry of the calcaneus (speed of sound). Daily physical activity was assessed using the Japanese version of International Physical Activity Questionnaire short version. After getting the International Physical Activity Questionnaire results, we classified participants into three categories (low/moderate/high) according to a protocol. Participants categorized into the low group according to the International Physical Activity Questionnaire were considered to be in the low physical activity group and those categorized into the moderate and high groups were considered to be in the moderate to vigorous physical activity group. RESULTS: Speed of sound was significantly higher in the moderate to vigorous physical activity group (moderate to vigorous physical activity versus low physical activity, 1533 m/s versus 1523 m/s, p = 0.03). Daily physical activity was significantly associated with speed of sound, even after adjustment for confounding factors and prognosticators (β = 0.195, p = 0.02). CONCLUSION: Sonographically measured bone status was significantly higher in women who were physically active than in those who were physically inactive, suggesting that daily physical activity might help to maintain good bone status.