The short answer to this question is "almost everywhere". As this is not really a scientific or very instructional answer I have worked on a more comprehensive breakdown with some anatomical explanations for you. The kettlebell swing is worth the time invested which many seasoned lifters can attest. Andy Bolton uses it and women also seem to like this type of exercise more than working with a barbell

Overall the kettlebell swing works for about 600 muscle groups as it is a compound movement just like the deadlift, bench press or squat which activate multiple muscle groups at once. 

 

While this number might seem excessively high think about your feet and hands and back muscles around the spine which are involved in the swing. A basic anatomy class will give you an idea on how many different little muscles are located in these areas which are activated during the swing. 

 

A longer, but not complete list of the muscle groups and muscles addressed by the swing

 

 

You will find many coaches refer to the posterior chain and that it is often being not trained enough in conventional programs. Some of the main muscles in the posterior chain are the biceps femoris, gluteus maximus, the erector spinae muscle group, trapezius, and posterior deltoids.

 

The biceps femoris is located in the thigh and is part of the hamstrings muscle group. The biceps femoris helps you to perform knee flexion and hip extension.

 

The Gluteus maximus is often lumped together with the gluteus medius and minimus as the "glutes" in fitness articles and among bodybuilders and powerlifters. The gluteus maximus is what mainly forms your buttocks. SO if your aim is to have a nice ass, the kettlebell swing helps. One of its main functions is to help you stand and take the weight of your body. It also helps when you need to get your body upright after falling down.

 

The erector spinae muscle group is made up of three muscles called the Iliocostalis, longissimus and spinalis and runs along the back of your spine. This muscle group helps to keep the spine in place and be more upright.

 

The trapezius is located at the back around your shoulder blade. It helps with three main functions which are supporting the weight of the arm, retracting the shoulder blade and rotating it. 

 

The deltoids, also referred to as "delts" are the muscles situated at the top of your arm where it attaches to the trunk. It might also be referred to as the common shoulder muscle. Most often it is being anatomically divided three ways into the anterior, lateral and posterior part. Its original name was coined through the similarity in form and shape to the Greek letter delta. Its function is to move the arm up.

 

The external obliques is what most commonly being referred to as the "six-pack". Technically it is an eight-pack which forms the outermost part of the three big muscle of the abdomen, the external obliques, internal obliques and transversus abdominis. The main function of the external obliques is to pull the chest downwards to compress the abdominal cavity. Strictly speaking, it keeps you from popping open and spill your guts. 

 

The internal obliques are between the external obliques and the transversus abdominus. Its main function is to work together with the diaphragm to make you breathe. The back and forth between these two antagonistic muscles creates the resistance and room fir air to fill the lunges and be exhaled. 

 

The transversus abdominis is a deep muscle which many fitness instructors belief to be a significant component of the core. It is the innermost of the flat muscle of the abdomen sitting beneath the internal oblique muscle. In women, it helps to deliver a child. For powerlifters, it is essential to building tension and stability in the midsection of the body for very heavy lifts. So deadlifting and giving birth has something in common in the ned, abdominal pressure.

 

The diaphragm is the skeletal muscle which sits below the heart and lunges and separates them from your lower abdomen where your intestines sit. When it contracts, the space for your lungs increases and therefore air is drawn into the lungs.

 

The rotator cuff is also a simplified version of calling a specific group of muscles by one name rather than their individual ones just like with the glutes. The muscles in the rotator cuff are the Supraspinatus, Infraspinatus, Teres minor and Subscapularis. If you find to learn them by heart you can remember "Which muscle sits in the rotator cuff?" As a group, the rotator cuff is responsible for moving and rotating the upper arm. 

 

The Rhomboids are two muscles the rhomboid major and minor. Their main function is to retract the shoulder blade.

 

The latissimus dorsi is a large flat muscle on the back which is partly covered by the trapezius. This is the muscle you train when you want to have "Bat Wings". In gym language, they are also commonly referred to as lats. Latissimi dorsi comes from the Latin word latissimus which means broadest which reflects its appearance on the back. Its main function is the movement of the shoulder joint in various directions. 

 

The quadriceps femoris, also referred to as "quads" among bros, is a large muscle group at the front of the legs consisting of four muscles. Their names are rectus femoris, vastus lateralis, vastus medialis and vastus intermedius. All of these muscles are extensors of the knee joint playing a major role in walking, running, jumping and squatting. 

 

As you can see the kettlebell swing trains a lot of muscles which will make you one strong or sexy person, depending on your training goals.

 

 

When you talk about swings there are different types of swings to consider. The main variations are

 

Standard Swing

One arm swing

Double kettlebell swing

 

The standard swing will put more emphasis on the glutes and the obliques if performed correctly. When executed correctly you will have a big force pulling on you in both directions on the upward and downward movement of the swing. This will be compensated by flexing your glutes and obliques at the top of the swing. 

 

The one arm swing will not create as much force as the standard swing but a bigger pull to the left or right. To stabilize this your internal obliques and transversus abdominis will have to work harder and you will get more core activation at the expense of the glutes and quads.

 

Finally, the double kettlebell swing will put the glutes and abs comparatively on the back bench and put more focus on the quads. This is mainly due to the fact that your stance has to be a lot wider to get two kettlebells between your legs and control them. Therefore you can get less momentum out of squeezing your glutes and the power comes more out of the quads.

 

All of these changes as small, but there. All of the different exercises address the areas aforementioned just with slight differences. Same principle as with the closed bench press to make the bench press more triceps than pectoral heavy (moving focus from the chest to the arms).

 

 

The list of targeted muscles in the kettlebell swing is long. If you wanted a gym was all the machines in it that address the same groups you will spend thousands of Euros or Dollars. A kettlebell comes in at 100 to 200 depending on the size and with these prices, I am talking big kettlebells which you do not find at your local gym.