Standing back weakness in 1-year-old babies may be related to too little exercise, malnutrition and spinal muscular atrophy. 1. Too little exercise: As parents are worried that their 1-year-old babies will fall and get hurt, they thus limit their babies’ daily activities, resulting in insufficient exercise for the babies. As a result, there will be a phenomenon that 1-year-old babies may suffer from standing waist weakness due to the lack of proper exercise for their muscles. 2. malnutrition: due to insufficient breastfeeding or the baby’s diet structure is more single, may lead to the baby’s nutrition is not balanced, lack of vitamin D, lack of calcium and so on. As a result, the baby’s bone and muscle development will be slower, so that the baby may have standing waist weakness. 3. spinal muscular atrophy: spinal muscular atrophy is mainly manifested as muscle weakness, muscle tone weakness, may lead to the baby to stand waist soft. When a 1 year old baby appears to have standing waist weakness, parents should take the baby to the doctor in time, by the professional doctor to clarify the cause of the disease and carry on the treatment.