Why Do Sit Ups Hurt My Thighs? (5 Factors to Consider)

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Should you notice that sit ups are causing pain in your thighs, this is the reason and the solution for it.

The main reason that sit ups hurt your thighs is because you’re not isolating your abs. Most ab exercises where your back is flat on the floor, or your legs are the primary mover, will involve using your hip flexors. So, your hip flexors are generally working much harder than your abs. Plus, your hip flexors are connected to your thigh-bone. Hip flexor activation is actually increased when you have your feet anchored or when performing decline sit ups.

You’re Using Your Hip Flexors Rather Than Your Abs

If you’re feeling sit ups in your thighs then you’re activating your hip flexors more than your abs.

Personally, I’ve never been a fan of sit ups, as I feel they tend to place stress on various body parts, while not isolating the abs as well as many other ab and core exercises.

Probably, the most common complaint about sit ups is lower back pain.

However, many people find that their legs tend to tire during sit ups well before their abs.

Realistically, what’s happening here is that either you’re not isolating your abs at all, or your abs have simply fatigued already.

So, in effect, once your abs have fatigued, you’re now using your hip flexors to raise your torso from the ground.

You can probably continue performing sit ups like this for quite a while, but you’re no longer using your abs.

Plus, it’s important to remember that the largest hip flexor muscle, the iliopsoas, is connected to the top of the thigh-bone (femur).

Therefore, if you’re using your hip flexors, as opposed to your abs, when performing sit ups, it won’t be long before your thighs start aching.

As I say, I’ve never been a fan of sit ups, and I will reveal some better ab exercises in a moment.

However, for now, if you choose to perform sit ups, then you’ll really need to concentrate on contracting and using your abs.

In reality, you’ll probably perform far less sit ups then you typically aim for before you stop using your abs.

Once you get to this point the set is over.

Most exercises will hit various muscle groups anyway, so it’s important to always stop a set when you feel the main target muscle is no longer being worked.

Are You Anchoring Your Feet?

Something else to consider is what you’re doing with your feet during sit ups.

I know many people choose to do sit ups with their feet anchored to a sturdy object.

This could mean that your feet are tucked under a sofa, a pair of dumbbells, or even a specific foot rack found on various pieces of equipment in the gym.

Unfortunately, when you anchor your feet during sit ups you’re actually stimulating your hip flexors even more than usual.

If you anchor your feet during sit ups you will automatically activate your thighs and hip flexors.

Basically, you’ll tend to pull with your feet in order to raise your torso during sit ups.

I would actually say that anchored-feet sit ups are even worse than conventional sit ups when it comes to isolating your abs.

In reality, most people tend to perform many more reps when their feet are anchored.

In a way this is making sit ups easier.

However, it’s highly unlikely that you’re using your abs, even from the first rep.

Now, don’t get me wrong, there are many of you who feel fantastic ab activation during feet-anchored sit ups.

But, much the same as any other exercise, you have trained yourself with good habits to ensure that you’re targeting the correct muscle group.

With that being said, I still believe that the vast majority of people perform sit ups, especially with feet anchored, and simply use their hip flexors and thighs to move themselves.

Are You Doing Decline Sit Ups?

Decline sit ups are a harder version of the regular sit up.

Basically, you’re having to work slightly against gravity too.

However, most decline sit up benches once again require you to anchor your feet.

So, in effect, you’re now performing a harder exercise, while anchoring your feet at the same time.

If you don’t have the required ab strength you’ll automatically end up using your feet, hip flexors, thighs, and lower back to perform the exercise.

I’m sure you can see how terrible this is, as you’re pretty much using every surrounding muscle group bar your abs in order to perform decline sit ups.

For me, if you’re still struggling to perform standard sit ups without using your hip flexors and thighs, then you definitely shouldn’t be doing the decline variation.

Place a Ball Between Your Legs

Here’s a little trick to try if you feel sit ups in your thighs.

Basically, what you want to do here is to activate the abs, while taking the focus away from your legs.

Weirdly enough, one of the best ways to achieve this is by placing something between your thighs.

I have a preference for a light medicine ball.

So, place the medicine ball between your thighs, squeeze your thighs together hard, and keep the medicine ball in place throughout your set.

You’ll want to squeeze and contract both your abs and glutes hard while performing your set.

This will immediately take the stress of your hip flexors and place it on your core muscles as a whole.

If you perform sit ups in this way correctly you’ll typically find that your abs fatigue much quicker.

However, I’ve never viewed ab training as the total number of reps performed.

Additionally, a great ab workout doesn’t even need to take that long either.

I would much rather perform 5 reps of sit ups that completely target my abs than 20 reps whereby I’m using my hip flexors and thighs.

So, give the medicine ball squeeze a try and you’ll immediately notice the difference.

Better Exercises to Isolate the Abs

Okay, I’ve mentioned that I’m not really a fan of sit ups.

In truth, I’m not a massive fan of crunches either, but they are still so much better than sit ups if you target your abs correctly.

For me, both sit ups and crunches use the lower back, hip flexors, and thighs much more than the abs.

And this is regardless of how hard you try to isolate your abs during the exercises.

In fact, there are a plethora of exercises that not only protect your hip flexors and lower back, but they also work the abs to far greater effect.

Choose 2-3 of the following exercises for an ab workout. Change up the exercises whenever you feel like it. 

Weighted Planks
Hanging Leg Raises 
Hanging Leg Raises with Medicine Ball between thighs
Ab Walkouts
Ab Rollouts
Russian Twists 
Pallof Press

Key Learning Points

  • It’s likely that you’re activating your hip flexors an thighs, as opposed to your abs, when performing sit ups.
  • This thigh and hip flexor activation can be made worse by anchoring your feet or performing decline sit ups. Once more, it’s unlikely that you’re actually activating your abs.
  • Place a medicine ball between your thighs and squeeze hard when performing sit ups. This will help you to activate your abs to greater effect.
  • Sit ups are NOT the greatest ab exercise and there are many others which are far better for your abs, and your overall spinal health.
  • Perform exercises which isolate your abs better, e.g planks, hanging leg raises, ab rollouts, pallof press, etc.

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