Hypotonia is the medical term for decreased muscle tone.
Healthy muscles are never fully relaxed. They retain a certain amount of tension and stiffness (muscle tone) that can be felt as resistance to movement.
For example, a person relies on the tone in their back and neck muscles to maintain their position when standing or sitting up.
Muscle tone decreases during sleep, so if you fall asleep sitting up, you may wake up with your head flopped forward.
Hypotonia isn't the same as muscle weakness, although it can be difficult to use the affected muscles.
In some conditions, muscle weakness sometimes develops in association with hypotonia.
It's most commonly detected in babies soon after birth or at a very young age, although it can also develop later in life.
Hypotonia present at birth is often noticeable by the time a child is 6 months old, if not before.
Newborn babies and young children with severe hypotonia are often described as being "floppy".
Signs of hypotonia in a child include:
A child with hypotonia often takes longer to reach motor developmental milestones, such as sitting up, crawling, walking, talking, and feeding themselves.
An adult with hypotonia may have the following problems:
Hypotonia is a symptom rather than a condition. It can be caused by a number of different underlying health problems, many of which are inherited.
Hypotonia can also sometimes occur in those with cerebral palsy, where a number of neurological (brain-related) problems affect a child's movement and co-ordination, and after serious infections, such as meningitis.
In some cases, babies born prematurely (before the 37th week of pregnancy) have hypotonia because their muscle tone isn't fully developed by the time they're born.
But provided there are no other underlying problems, this should gradually improve as the baby develops and gets older.
Read more about the causes of hypotonia.
If your child is identified as having hypotonia, they should be referred to a specialist healthcare professional, who will try to identify the cause.
The specialist will ask about your family history, pregnancy and delivery, and whether any problems have occurred since birth.
Read more about how hypotonia is diagnosed.
Depending on the cause, hypotonia can improve, stay the same or get worse over time.
Babies with hypotonia that results from being born prematurely will usually improve as they get older.
Babies with hypotonia caused by an infection or another condition will usually improve if the underlying condition is treated successfully.
Unfortunately, it's often not possible to cure the underlying cause of hypotonia.
Hypotonia that's been inherited will persist throughout a person's life, although the child's motor development may steadily improve over time in cases that are non-progressive (don't get worse).
Read more about treating hypotonia.