Daily Physical Activity Program Increases Bone Mineralization and Growth in Preterm Very Low Birth Weight Infants

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Abstract
Objective. A study of daily physical activity was performed with 32 preterm infants to evaluate changes in body weight and bone mineralization. Study Design. Subjects were matched by birth weight and gestational age and randomly assigned to the physical activity (PA;n = 16) or to the control (C; n= 16) program. PA consisted of range of motion against passive resistance to all extremities for 5 to 10 minutes daily. Peripheral dual-energy x-ray of the right forearm (ulna and radius); biomarkers of bone formation (serum type I collagen C-terminal propeptide [PICP]) and resorption (urine pyridinoline cross-links of collagen [Pyd]); serum calcium, phosphate, alkaline phosphatase, parathyroid hormone (PTH), and 1,25-(OH)2 vitamin D; and urine levels of calcium, phosphate, and creatinine were obtained. All measurements were made at study entry and at 2.0 kg of body weight. Results. Despite a similar nutrient intake at advised levels for preterm infants, gains in body weight (g) and forearm bone length (cm), bone area (BA; cm2), bone mineral content (BMC; mg), and fat-free mass (g) were greater in PA infants. Forearm bone mineral density and fat mass gains did not differ between groups. Serum PICP levels remained constant in PA infants but decreased in C infants suggesting a slower rate of bone formation. Urine Pyd or bone resorption activity was similar between groups. A higher level of serum PTH was observed in PA infants at 2.0 kg of body weight; however, the change from study entry to completion did not differ between groups. All other serum and urine values were similar and within normal limits. Conclusion. A daily PA program promotes greater gains in body weight, forearm length, BA, BMC, and fat-free mass in premature infants.