The Effect of Physical Activity on Bone Strength and Immune System in Very Low Birth Weight Infants: is More Really Better??

Infants will be randomly assigned to one of 3 study groups. Group 1 - physical activity once a day. Group 2 - physical activity twice a day and group 3 - control.

The physical activity program is based on the Moyer-Mileur et al protocol (1). Briefly, this protocol involves extension and flexion range-of-motion exercise against passive resistance of both the upper and lower extremities. Both extension and flexion were performed five times at the wrist, elbow, shoulder, ankle, knee, and hip joints (about 10 minutes for each session). Infant in group 1 have the physical activity intervention once a day, 5 days a week. Infant in group 2 will have the same physical activity intervention twice a day, five times a week. Infant in group 3, the control group will have a similar time (10 minutes) of daily interactive periods of holding and stroking without range-of-motion activity.

The physical activity will be done by the same person (the NICU physiotherapist) Growth parameters, and bone strength, will be measured at enrollment and every 2 weeks till discharge.

Bone strength assessment will be determined by quantitative ultrasound measurement of bone speed of sound (SOS) at the middle left tibial shaft (Sunlight Omnisense Premier). All measurements will be performed by the same person, who will be blinded to the group assignment.

Cytokines study In a sub-group of patients who will have arterial line at enrollment blood sample ( 0.6 CC) will be drawn before and immediately following activity for assessment of proinflammatory (IL-6) and anti-inflammatory ( IL1-ra) cytokines. Samples will be kept at -20º C and will be analyzed after completion of the study.