The goal of this interventional study is to investigate through musculoskeletal ultrasonography how the thickness and muscle trophism in infants aged 28 to 35 weeks undergoing infant massage compared with a group of infants with similar characteristics not subjected to treatment.

The main questions it aims to answer are:

• To assess by musculoskeletal ultrasound the impact of infant massage on muscle thickness muscle. Specifically, changes in muscle thickness and trophism of the quadriceps femoris.
• Potential effects on spontaneous motility and stature-ponderal growth of infants. In addition, the discomfort and behavioral status of the infant before and after massage will be investigated infant.

Patients included in the study will be randomized according to a random sequence with a 1:1 ratio into theexperimental group (GS) or the control group (GC). Patients in the GS will perform therapy with infant massage in addition to the usual rehabilitation therapies as specified by the program individual habilitative, to which patients in the control group will be subjected exclusively control.

Infant massage will be performed three times a day (10 minutes per session) until they reach the 35th week of post-conceptional age (35+6) by the two departmental physical therapists (ADP and ADV).

Ultrasound will be performed at the time of randomization (T0) and then 1 time per week until the 35th week by two operators (SN and VA); at the same time, the circumference of the thigh subjected to ultrasound examination. A 12Hz linear ultrasound probe will be used, applied perpendicular to the skin. The infant will be placed supine, with the thigh extended, in a neutral position; excessive compression will be avoided by applying a generous amount of gel. At the midpoint of the thigh, the thickness of the quadriceps muscle will be calculated by measuring the distance between the cortex of the femur and the most superficial muscle fascia. The average of at least 2 measurements will be then calculated. The Heckmatt scale will be used to assess the echogenicity of muscle and bone. In addition, at time T0 and at week 35 the following data will be collected: weeks gestational age, weight at birth and at the end of treatment, rectal temperature, blood gas parameters if present.

Inclusion Criteria:

• gestational age between 28and 35 weeks;
• day of life ≥ 7 (to ensure passing the transition phase);
• clinically stable infants, either in spontaneous breathing or ventilatory support invasive or noninvasive, with a good ability to regulate states and good stress management.

Exclusion Criteria:

• Brain pathologies;
• Dysmorphisms;
• Clinically unstable patients requiring treatment with inotropes and/or nitric oxide nitric acid and/or drug therapy for closure of the ductus arteriosus of Botallo.