 Briefly our study is looking at the effects of 4 weeks of assisted exercise on the body composition and neurologicalbehavioral development of healthy growing premature infants enrolled between the ages of 30-33 weeks. It is a blinded study where the active group gets the exercise intervention and the control group is cuddled for the same amount of time -approximately 20 minutes. We get baseline data using muscle ultrasound, bone speed of sound and DEXA. We also get baseline blood samples to look at inflammatory mediators and growth hormone. Video of each subject is recorded an hour at two time points during the study to assess the babies for spontaneous activity. Nutritional intake information is collected daily and in the 4th week of the study assessments made for total energy expenditure using doubly labeled water. At this point in the study we repeat the ultrasounds and DEXA for comparison. Finally in the period just before discharge we do a complex neurological exam using the Brazelton NBAS assessment. 