Hypotonia is a state of reduced muscle tone, usually related to the skeletal muscles. Hypotonia ranges from mild to severe in people who have Down syndrome, although muscles tend to strengthen with age.

Young children with Down syndrome often have hypotonia throughout their bodies.

Babies with Down syndrome often have delays in reaching physical developmental milestones, such as rolling over, sitting up, crawling, or walking. Constipation may also frequently occur, caused by weak intestinal muscles that move stools more slowly through the digestive tract.