The martial arts adjust to your body not the other way around. They were designed to use technique, timing, leverage, and knowledge of the human body, not strength.
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Maybe he is just stronger. There will be someone that is stronger. Maybe he has been training or exercising more to get stronger. This question has nothing to do with martial arts.
Start working out buddy
You need to change your diet, eat more protein and in a month you will see a difference.
