Perhaps the most general principle underlying human movement is that people prefer to move in ways that minimize their energetic cost. Although aspects of this preference are likely established over evolutionary and developmental timescales, we recently discovered that the nervous system can continuously optimize cost in real-time. Here I will present our new research focused on uncovering the mechanisms underlying the initiation of this optimization, as well as its process. Our collective findings indicate that energetic cost is not just an outcome of movement, but also plays a central role in continuously shaping it.