Knee Touch Crunch: Benefits, Muscles Worked, and More

published by: Debbie Luna
Last Updated:
December 16, 2022

Having six-pack abs is a goal aimed for by many gym buffs, and one exercise that helps achieve such a goal is crunches. Although there are many variations to this workout, all of them are able to target the rectus abdominis muscle, which is responsible for ab definition. 

The knee touch crunch, a variation of the crunch, is a simple and straightforward bodyweight exercise that targets the core muscles, primarily the rectus abdominis. This exercise has the advantage of requiring no additional equipment while still being very effective at strengthening the core muscles.

While the knee touch crunch may be easy to execute, there are important mistakes to avoid in order to optimize the workout. Furthermore, if these mistakes are avoided, they may also reduce the risk of muscle strains.

What is a Knee Touch Crunch?

The knee touch crunch is an upper-body isolation exercise that is very effectively designed to build core strength and target the abdominal muscles.

knee touch crunch

It relies on body weight and gravity to act as resistance, but the exercise can be further advanced through different hand positioning. 

How to Perform a Knee Touch Crunch

To perform knee touch crunches, assume the starting position by lying supine on the floor. Bend the knees at about 90 degrees, and plant the feet firmly on the ground. Extend the arms forward with the palms facing down, reaching towards the knees.

Start the movement by contracting the abdominal muscles. Lift the shoulders off the floor and let the hands travel toward the knees. Keep the chin tucked in for the whole exercise to keep the neck muscles from getting strained. When the palms are on the knees, lower the upper torso back to the ground to complete a repetition. Repeat the maneuver until a set is completed.

When it becomes too easy to perform, the starting position may be modified to add more resistance. Instead of starting with the arms reaching for the knees, the exercise may also be performed starting with the arms extended overhead. This makes the exercise more challenging and may be utilized as a progression to avoid hitting plateaus.

Muscles Worked in a Knee Touch Crunch

The primary muscle worked in the performance of knee touch crunches is the rectus abdominis muscle. The rectus abdominis is the uppermost layer of the abdominal muscles. It is also called the "abs" and the "six-pack."

knee touch crunch muscles

Knee touch crunches also engage other abdominal muscles such as the internal and external obliques and the transversus abdominis muscles. The difference in muscle activation between crunches and sit-ups is that crunches are isolation exercises for the abdominals, whereas sit-ups also recruit the hip flexors.

Benefits of a Knee Touch Crunch

Can be Performed Anywhere

As a bodyweight exercise, a primary benefit of the knee touch crunch is that it can be performed virtually anywhere with a stable, flat surface to lie on. Others may prefer to use a bench when performing this workout; however, the floor is a suitable surface for a knee-touch crunch.

Defines the Abs

The knee touch crunch and many other variations of the crunch are used to define the rectus abdominis to create what is called the “six-pack abs.” Although the exercise may seem too simplistic, the knee touch crunch is actually able to burn fat in the abdominal area while also strengthening and defining the muscles.

Enhances Stability

Because the knee touch crunch works the core muscles and therefore strengthens them, this exercise is also able to improve stability. This thought is supported by a study published in 2018 where it is stated that core strengthening exercises are able to positively influence core stability.

Mistakes to Avoid When Doing Knee Touch Crunches

Jutting the Chin to the Ceiling

Neck positioning while doing crunches is a crucial factor to avoid straining the muscles of the neck, which in turn leads to a sore neck after the workout. Make sure that the movement of the crunch is not led by the neck muscles, as it should be in line with the body at all times. 

The proper position of the neck should be slightly tucked as if there were a ball placed between the chest and the chin and you were trying to hold that ball still.

Not Activating the Core Muscles

Before doing a crunch, it is vital that the core muscles are first activated. A lack of core engagement prior to performing the crunch may lead to an improper and unstable technique. 

To fix this, first, tuck the belly in without having to hold your breath while doing the crunch. This will cause a stabilization action of the abdominal muscles which will support the movement.

Using Momentum

A common mistake for crunches is using momentum to lift the upper back off the mat to perform the crunch, and then performing it too fast. This comes from the misconception that doing faster reps gives better results. On the contrary, slower and steadier reps while doing crunches are better.  It can be observed that the abdominals burn more when performing them in this manner.

This is because a slower pace with more controlled movement will eliminate the generation of momentum to lift the upper back. Hence, the exercise will recruit more of the abdominal muscles to generate power. 

Arching the Back

Like most other exercises, arching the back is a common mistake, especially with individuals that perform workouts or lift weights that are too heavy for their current fitness level. With crunches, the lower back is expected to stay in contact with the mat or the floor, thus the lower back should not arch. If this cannot be achieved, try reducing the level of exercise through minor modifications, such as starting at an incline. 

Sitting Up

As mentioned above, when crunching, the lower back is expected to stay in contact with the floor at all times. Only the upper back should be off the mat in the process of a crunch. A full sit-up is not necessary, as this does not work the abdominals but rather relies on the hip flexor muscles to lead the movement as soon as the upper back leaves the mat. 

Final Thoughts

The knee touch crunch is an ab-focused, core-strengthening, upper-body isolation exercise. This workout is great for building abdominal muscles and doesn't call for any special equipment. Although it uses the user's own weight as resistance, the pressure and resistance level may be increased by shifting where the hands are held.

Furthermore, because it is a low-impact exercise, the risk of injury is low. However, caution must still be observed since crunches require flexion of the spine, which may cause unnecessary strain on the back or neck.


1. Hsu SL, Oda H, Shirahata S, Watanabe M, Sasaki M. Effects of core strength training on core stability. J Phys Ther Sci. 2018;30(8):1014-1018. doi:10.1589/jpts.30.1014

Debbie (Deb) started powerlifting and Olympic lifting in High School as part of her track team's programming; She continues to train in order to remain athletic. Inspire US allows Deb to share information related to training, lifting, biomechanics, and more.
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