| Peak bone mass in women occurs at 16 to 30 yrs, in part dependent on nutrition and exercise. Pregnancy may stress body calcium economy through fetal calcium needs, and increasing bone weight. Bone is stimulated by compression, e.g. tennis, as load-bearing exercise. Tennis may decrease bone resorption, through intermittent short high mechanical loading. The playing arm is impacted from swinging forearm grip, and ball contact. The calcaneus receives ground reaction forces, from sudden starts and stops at heel strike. The purpose of the study is to test the thesis that maternal bone mineral density of pregnant women who participate in a load-bearing exercise such as recreational tennis increases during pregnancy. Bone mineral density (BMD) measures of the radii and calcanei used dual energy x-ray absorptiometry (DEXA) at <12 wks gestation and 2--4 wks postpartum. Ultrasound of calcanei, and hand grip strength were measured at <12, 20--24, 33--36 wks, and 2--4 wks postpartum. Speed of sound (SOS) and broadband ultrasonic attenuation (BUA), bone properties reflective of density and structure respectively, are combined as Stiffness Index (SI) referent to a normal 20 yr. value: SI = 0.67(BUA) + 0.28(SOS)-420. Age, height, and weight were not different between groups. At <12 wks, tennis players' left calcaneus BMD was higher vs. controls 0.56 +/- 0.08 vs. 0.40 +/- 0.07 g/cm2, (p = 0.017). BMD fell to values not different from controls at 2--4 wks postpartum. SI values for left calcanei were higher in tennis players vs. controls at <12 wks (SI, 108.0 +/- 19.20 vs. 84.9 +/- 15.17, p = 0.033), but fell to values not different from normal at 20--24 wks, 33--36 wks, and 2--4 wks postpartum. In the upper limbs, DEXA measures of BMD, at 3 different radial sites, 1/3, mid, and ultra distal showed no difference between tennis players vs. controls for dominant, or non-dominant hand at <12 wks and 2--4 wks postpartum. Hand grip strength was not different between tennis players vs. controls. Tennis players generally stopped playing in the third trimester by own choice. Thus, a period in pregnancy when tennis is reduced, is associated with a drop in fast bone measures, despite the counter load-bearing effect of pregnancy itself in late pregnancy. |
