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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?

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 a couple of descriptions:

Baby straightening their body

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.


When babies stretch, like we do, it can look like they are tensing up.

Tensing tummy

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.

This and so much more...

Best For Mums have created a wide range of product guides to helps parents, and here’s a selection:

Infantile spasm

A different kind of baby tensing up is known as a spasm 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

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.

Other baby condition articles

We’ve covered a few other articles relating to conditions baby’s can experience, check them out:

What is going on when a baby is tensing up?

We will never quite know exactly what is going on when you have a baby 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 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.


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 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. 

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 but you can speak with your GP or paediatrician if you feel the constipation is problematic

Baby wants to stand up

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. If they’re tensing 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 tense up in the high chair and when lying down which results in them tensing up and 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

A 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.


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 then medical attention should be sought.

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