My Baby Seems Too Stiff (Hypertonia)
The short answer
Hypertonia means your baby's muscles feel unusually tight or stiff, making it hard to bend or move their limbs. While some stiffness can be normal during certain movements (like when a baby is startled or upset), persistent stiffness at rest warrants evaluation. Early identification and physical therapy can make a significant difference.
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By Age
What to expect by age
0-3 months
Newborns naturally have some degree of flexor tone, meaning their arms and legs tend to curl inward. This is different from hypertonia, where the limbs feel rigid and resist being moved. Signs to watch for include a baby who feels like a board when you pick them up, whose legs scissor or cross when held upright, or who arches their back strongly and frequently. Some stiffness during crying or startling is normal, but stiffness at rest is not.
3-6 months
As normal newborn flexor tone decreases, you should be able to gently extend your baby's arms and legs without much resistance. A baby with hypertonia may still have tightly fisted hands past 3 months, resist having their arms or legs straightened, or arch their back when you try to hold them in a seated position. These babies may have difficulty with tummy time because they cannot relax enough to push up comfortably.
6-12 months
Babies with hypertonia may have difficulty reaching motor milestones like sitting, crawling, and grasping objects. Their movements may look stiff or jerky rather than smooth. You might notice that their legs feel very tight when you try to open them for a diaper change, or that they consistently point their toes. Physical therapy at this stage focuses on stretching, positioning, and encouraging relaxed movement patterns.
12+ months
Persistent hypertonia affects walking and other gross motor skills. A toddler with high muscle tone may walk stiffly, have difficulty with balance, or walk on their toes. Ongoing physical therapy is important, and your pediatrician may refer you to a pediatric neurologist to determine the underlying cause. Many children with mild hypertonia respond very well to therapy and make excellent progress.
What Should You Do?
When to take action
- Your baby stiffens briefly when startled, excited, or upset, but relaxes at rest.
- Your baby has some normal newborn flexor tone but you can gently extend their limbs without significant resistance.
- Your baby occasionally arches their back during fussiness or gas but is otherwise relaxed and moves freely.
- Your baby feels strong and firm but is meeting motor milestones on time.
- Your baby's limbs feel consistently stiff and resist gentle bending, even when your baby is calm and relaxed.
- Your baby's hands are tightly fisted past 3-4 months of age and they have difficulty opening them to grasp objects.
- Your baby arches their back frequently during feeding or when held, and this seems involuntary.
- Your baby's whole body stiffens and their legs scissor when held upright, or they feel like a rigid board when picked up.
- Your baby has stiffness accompanied by difficulty feeding, breathing problems, or seizure-like episodes.
Sources
Related Resources
Trust your instincts. If something feels wrong, reach out to your pediatrician.
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Related Physical Concerns
My Baby Seems to Use One Side More Than the Other
Babies should use both sides of their body fairly equally during the first 18 months of life. While slight preferences can be normal, a consistent pattern of favoring one side - using one arm much more than the other, crawling with one leg dragging, or turning the head predominantly one way - should always be discussed with your pediatrician. Early identification of asymmetry leads to the best outcomes.
My Baby Only Army Crawls
Army crawling (also called commando crawling) is a completely valid and normal way for babies to move. Many babies army crawl for weeks or even months before transitioning to hands-and-knees crawling, and some skip hands-and-knees crawling entirely. What matters is that your baby is independently mobile and exploring their environment.
One Side of My Baby's Body Moves Differently
Babies should generally use both sides of their body equally. If one side consistently moves differently, is weaker, stiffer, or less coordinated, this warrants evaluation. Asymmetric movement can indicate hemiplegia (cerebral palsy affecting one side), brachial plexus injury, or other neurological conditions that benefit from early therapy.
My Baby Crawls Unevenly
While some variation in crawling patterns is normal, consistently favoring one side or dragging one limb while crawling warrants attention. Babies should use both arms and both legs relatively equally when crawling. Persistent asymmetry could indicate muscle tone differences, hip issues, or neurological concerns that benefit from early evaluation.
My Baby Still Has the Fencing Reflex (Persistent ATNR)
The asymmetric tonic neck reflex (ATNR, also called the fencing reflex) causes your baby to extend the arm on the side they are looking toward. It should integrate between 4-6 months. If the ATNR persists strongly beyond 6 months, it can interfere with bringing hands to midline, bilateral hand use, and rolling. Evaluation is recommended.
Signs of Ataxia in Babies and Toddlers
Ataxia refers to wobbly, uncoordinated movements that result from problems with the cerebellum (the brain's coordination center). Signs include an unsteady, wide-based gait, difficulty with precise hand movements, and intention tremor (shaking that worsens when reaching for something). If you notice these signs, evaluation by a pediatric neurologist is important.