it meant you are using localized arm muscle in the most normal way, i.e. like everyone else (non-martial). when i train with bokken or jo or axes/hammers, my legs, hips, and middle (below my sternum) tired before my upper body and arms. something you can try. hold your bokken in chudan/seigan position. have someone push the tip of the bokken toward you. imagine your body is like a giant balloon, michelin man, and let all the power of that push to into the ground beneath your feet. if you have tension in your body, then you will know from the feedback. so every time you swing the bokken, remember that feeling. it's what we called "bring the ground to the tip of your bokken". think of unbend able arm exercise, but with your arm now as long as the bokken or whatever weapon you held.

it could mean you have strong vitality, healthy, i.e. life force (doesn't mean that you know how to use it). or it could mean you have a strong feminine side in you.