as one

One of the most interesting, and hardest, things about martial arts is using the whole body as one complete unit. It's very easy to use say just an arm. And by extension it's just as easy to use that arm to lift consecutively heavier weights in order to build up the muscles and make the arm stronger. It is as easy as well to practice some set repetition of complex moves with the arm, until such moves become second nature.
It is much harder to move the arm in conjunction with the rest of the body. All the pieces; arms, hips, legs and feet, head, have to move in coordination and in synch.
When the whole body can be used as one single, completely coordinated entity, there is some serious leverage to be had. The arm can only move so far, so fast. Sure, the muscles can be developed, for a time. But eventually the muscles deteriorate as the body ages. But to move the arm whilst advancing from the hips and driving the trunk of the body, that can generate more speed and power than even the strongest, fastest arm.
Critical too is a sense of timing, both intra- and inter-body. Intra-body means timing amongst all the parts of the body such that the arms extends just enough in an arc while the hips turn and the legs move forward, such that the peak of the arm's arc is reached just as the hips and legs have moved their greatest distance. Miss the timing and the arm flails limply waiting for the body to catch up, or gets snapped by the body like a whip. Inter-body timing is the movement of one's body in relation to someone else's, generally the bad guy. The fastest, strongest movement is useless if done so early it is telegraphed to an enemy who easily dodges away and counters. It is also useless if a devastating attack is unleashed too late; the body stepped within killing range but the arm trailing behind, building up force and speed like a whip ready to crack, but too late, as the enemy has already engaged the parts of the body that have stepped defenseless into range.
I am not the fastest, nor the strongest. I doubt I ever will be. But that also does not matter. More importantly is to move with economy. Move if and when necessary; no earlier, no later. And move everything together; move from the center, the legs holding the body up, the head guiding, the arms connecting the sword to the whole.