You can look up “core muscles” and find that different people include different muscles in the group considered the “core muscle group”. But unless you are going to get that specific and train just one muscle in the group then you really don’t need to figure out which person is right. It would serve you just as well to do a variety of exercises that strengthen your “core” and more than likely you are going to be working the various different sets that the different people are including in the “core muscle group”. What can help is to think of the “core” not just as the abdominals. That is very limiting. If you think of the core as center from which you need to be strong and stable then you will possibly have a larger picture of what the core is and understand that it is more than just your abdominals.
You need a strong center to be stable and balanced while you are manipulating your limbs. If you keep that in mind you might realize that it is the back of your body as well as the front AND extending further down your legs than you first might have realized.
Doing a variety of crunches and sit-ups, including V-sit-ups and side crunches, will work your abdominals. Wood chops help with the entire trunk area. Push-ups are great because they require you to keep your abs tight for a great workout of them.
Bridges (lying on the floor and pushing your pelvis up), work the lower back muscles as well as the hips and glutes.
Lunges are great because they work your quadriceps and glutes. If you put some trunk twist into it with or without a weight you are adding another dimension to it and getting your trunk area.
Squats can help as they get the quads and glutes too.
Exercises that require you to balance yourself are going to help you with all those stabilizing muscles. These will strengthen your “core” as well as keeping it trained and at the ready for you when you need them to stabilize you.
So, do you really need to know that in a squat you are using your multifidus and quadratus lumborum (among other muscles) or does it just help to know that if you do them you are strengthening muscles that will assist you in having a strong a stable core? I believe it is good just to think about the “core muscles” as being the groups and groupings of muscles from the top of your chest down to your knees, front and back.
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