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Baby Tensing Up

For new parents, in particular, a baby’s behaviour can often be baffling. Especially as they can’t communicate their behaviour verbally, some of these things are often unexplained. In this article, we take a look at causes and some general advice on a baby tensing up.

What do we mean by baby tensing up?

When a baby stiffens its body up, it can be a sign that they are uncomfortable or feeling threatened, excited, or there may be an underlying medical condition. It’s important to learn what it looks like when a baby tenses up so that you can provide the appropriate support.

There are a couple of descriptions for baby tensing up and what you may be trying to look up may be different to another visitor. So here are a couple of descriptions:

Baby straightening their body and legs

This kind of baby tensing can be easily described as the baby making themselves stiff and straight. Depending on how they’re positioned it almost looks like they are standing up. They are tensing their muscles in their legs and often they will accompany this action with grunts. This can happen at any time and each episode tends to only last a few seconds.


Baby stretchingWhen babies stretch, like we do, it can look like they are tensing up.  Sometimes you may see your baby stiffening its body or your baby straightening legs or arms out in a stretching motion just like we do.

Tensing tummy

You may also have a baby tensing up in belly area. Some babies may just be tensing their tummy and when you look at their stomachs while they are tensing their stomachs don’t look quite as round as they usually do. This can often be accompanied by clenching their firsts, tensing their legs and shaking at the same time.

Infantile spasm

A different kind of baby tensing up is known as a spasm (or small seizure) and luckily we have a video here which can show if this is the kind of tensing you’re looking for information on.

Other descriptions

However, every baby is different, which means that baby tensing may look completely different from child to child. Understanding the different ways that baby tensing or stiffening may look can help determine how we can help. Here are some other descriptions we’ve gathered from real parents online

  • My baby started to clench his fists and tense his whole body and make a grunting noise. 
  • He is 5 months old and throughout the day he will be playing like normal and then all of a sudden he tenses his whole body up and makes a grunting noise!
  • My little one has recently started tensing up, straightening her arms and legs, and grunting.  It’s almost like she has stomach pain, but she is not pooping when she does it.
  • When he lays down he straightens arms and legs out and grunts.
  • Since my girl twin could sit up, she would tense up whenever we put her in the high chair, clench her thighs, pull her whole body inwards, her face would go red and hot and then she would appear to pass out!

Any of these sound familiar to you? If so, read on.

What is going on when a baby is tensing up?

Baby straightening legsWe will never quite know exactly what is going on when you have a baby or newborn tensing up and whether it’s voluntary or not. However, what we can imagine is the same if we tensed our muscles fully – the baby is engaging their muscles to their limit and contracting their bodies. 

Contracting muscles is what we do to release energy to perform actions but rarely do we ever need to contract them all at once when there’s no need.

This is why many parents are concerned when they see it. Are they in pain? Is it a normal baby development event?

Possible causes of your baby tensing up

baby tensing up

Before we go into details on possible causes of a baby tensing up we think it’s important to note here that a quick search online will make it obvious that it is a common thing to happen to a baby in their early development phase and often not a cause for concern. 

However, we are not medical professionals at Best For Mums and any information here should not be used as advice and genuine concerns should always be sought from your GP.


Baby teething

Teething is a big cause of a lot of problems for babies full stop and the pain and annoyance of it all can cause your baby to tense up if they’re having a particularly uncomfortable moment. 

At times I have known my baby boy has been irritable because of teething and when I see him tense up I put two and two together and move on. If your baby tenses up and is crying then this could be a leading cause of it.

Possible solutions: We recommend letting it pass without intervention but you can also use various teething aids to distract them.


Babies can get constipated often for a number of reasons, teething being one of them in fact. Being constipated is uncomfortable and can lead to some abdominal pain which can come and go in waves. Your baby tensing up and grunting during a particularly painful moment of constipation can be common, especially if you see them tensing up their tummy. This can sometimes be accompanied by grunting or a red face. 

Although constipation can be unavoidable there are some things you can do to relieve it if you feel this is a cause of the tensing.

If your baby follows baby led weaning or is in the middle of a growth spurt then constipation could be more common than usual.

Possible solutions: Again, we recommend just letting it pass naturally (a warm bath can often help) but you can speak with your GP or paediatrician if you feel the constipation is problematic

Baby wants to stand up

Baby wants to stand

If you’re baby is anything like mine then they will love to stand up on their legs with your support. This is especially true for babies who are particularly keen on bouncers, rockers and jumperoos. There’s just something about it that they love and get great joy to use their leg muscles properly. 

Most babies who are tensing for this reason will do it when they aren’t standing up, obviously, such as when they’re lying down, in a high chair or in a bath. When they do this, try picking them up and let them stand up with your support and see if it does the trick. Once you get to know your baby, tensing up their legs may become a familiar cue that you’ll know exactly what to do with!

Possible solution: Get your baby up on their legs safely or place them in a baby bouncer and let them get their kicks!

Over stimulation

We’ve seen a few mentions online of parents’ babies tensing up when they’ve had their senses overloaded in a short space of time and it’s just too much for them. Over stimulation happens when there’s too much going on at once and not a case of a heavy baby sensory class

Think about scenarios where you could be trying to feed them in a crowded room with the telly on and loud noises or music. If they stiffen up in a tense situation take them out of it to calm them down and see if the tensing up subsides.

Possible solution: Take your baby out of the tense situation and try and calm them down


It’s hard to believe but babies can sulk and demand to have something change. This can manifest itself in the form of tensing as they huff to get their own way. This is perhaps a characteristic of older babies who have the mental capacity to know to do this. 

We’ve found that babies can stiffen up in the high chair or when lying down (especially for tummy time) which results in them tensing up and grunting or crying. Try picking up your sulking babe and put them somewhere else and see if it stops it. Or, you can try to not give in and work through it but that’s probably going to lead to more upset to be honest.

Possible solution: Move your baby from what they don’t like or put up with it and take your chances

Tummy ache

Baby tense tummyA tummy ache can lead to your baby clenching and tensing up as they deal with the discomfort. This is slightly different from being constipated as there is still a presence of regular stools. Is your baby under the weather? This could be why they’re tensing up stomach and crying. 

Tricky one to diagnose and not one you should probably do yourself. If your baby’s stool is different than usual, running a high temperature or not quite themselves for a prolonged period then do not self medicate – seek medical attention straight away.

Possible solution: Do not attempt to self medicate – if symptoms persist please visit a GP for a diagnosis and medical help.


Babies suffering from reflux can sometimes tense up and grunt as they’re going through the motions. Chances are that if your baby has reflux then it won’t be the tensing that brings it to your attention. Things like bringing up milk, crying and fussing are the most common markers of reflux with tensing up being way down on the list.

Possible solution: Normally, reflux isn’t a problem and should pass, however if your baby is persistently suffering than seek medical attention is our advice as usual.


A buildup of farts can be quite painful before it passes which can be made worse if they are constipated as well. When a baby tenses up it can help to get that gas moving before the gas emerges at the other end!

Possible solution: Let the gas pass naturally or read our section above on constipation.

Burn off some energy

Have you ever woken up from a deep sleep to stretch your arms, tense your muscles and then stretch? Well, we think babies like to do that as well and it manifests itself with baby tensing up without grunting or crying. This is a completely innocent and harmless reflex and you shouldn’t worry. At times it may even be a pleasant thing to see.

Possible solution: No solution needed.

When to be Concerned

As we’ve seen, it is fairly normal for babies to tense up, stiffen, stretch, straighen their arms and legs, etc., and is usually not a cause for concern. However, we would not be doing our job if we didn’t at least mention that there are some cases of baby tensing up that are due to medical conditions that should be diagnosed and treated by a doctor. If you suspect one of these, please seek medical help. 

  • Infantile Spasms. A form of epilepsy that affects babies under 1 year old. We included a video earlier on of a baby having infantile spasms (also not to be confused with baby shudders). These are most notably recognised as being very short spasms but occurring at regular 5-10 second intervals for a period of time. If you notice this type of behaviour, be sure to contact your doctor.
  • Hypertonia. Muscle stiffness is the main symptom of hypertonia. If your baby has trouble moving their joints, such as bending their legs, then this could be the cause and something to explore further with your doctor.
  • Cerebral palsy. This is a disorder that effects a person’s ability to move and balance, and is difficult to diagnose in newborns. In addition to muscle stiffness and spasms or tensing up, common symptoms to look out for include delays in reaching development milestones, weak muscles and clumsy movements. 

Wrapping Up

We think that babies tensing up from time to time is a completely normal thing to happen and should not be a cause for concern. However, if you feel it doesn’t seem normal and resembles a seizure or prolonged stiffness, then medical attention should be sought.