For a more defined core I would do cable crunches, some form of leg raises, and decline sit ups! I would also make sure you're eating pretty clean because abs are really made in the kitchen!

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I would try to focus on adding muscle to your stomach aka abs. This won’t make your waist bulky and you really have to go through extra mile to make yourself look bulky trust

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What do you want to improve?

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If you want a thinner waist you don’t have to do much core because that can make it wider but definitely don’t skip fully. do glutes and legs if you want a more rounder shape at the hips and to make your waist seem thinner… but that’s just my experience. also make sure you work them upper glutes, a lot of people seem to skip them without knowing

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