Shintaido includes many jumping, hopping and walking movements with the center of gravity lowered (shin shin kaihatsu taiso 身心開発体操, literally "heart-mind and body opening exercises"). These exercises are a significant part of most Shintaido practices and are unique to Shintaido— no other martial art or movement discipline that I know of included such unusual ways of moving forward through space. But the precises purpose of these exercises remains a bit mysterious and might benefit from deeper analysis.
The phrase "moving forward through space" may be the key, since moving or jumping forward is typically emphasized more than, say, jumping as high as possible. Many of these movements call attention to the act of moving forward. In this age of mechanized transportation, we sometimes take the simple act of moving through space for granted— just step on the escalator, push the elevator button for the floor you want, or get in the car turn the ignition and put the pedal to the metal. We may forget the degree direct personal effort that was required to move from one place to another in past times.
On a more basic level, most people simply see what they want or where they want to go, and reach for it or walk to it. But even for people without a disability or injury, it wasn't always so easy. Imagine the infant we all once were, moving towards something intentionally for the first time, every resource it has engaged in the incredible struggle to move itself forward.
The infant represents our past, our earlier self, for whom moving forward through space was a challenging step along the path of engaging with the world. In some ways, the jumping exercises in Shintaido return us to that struggle. But we can look back further to the evolutionary past to consider the meaning of "going forward."
In the 1950s, the American neuroscientist Paul MacLean proposed the concept of the triune brain. While his ideas are no longer considered scientifically valid (see this article in Scientific American), his concept of a "reptilian brain"— an evolutionarily older structure that persists within our modern human brains and controls the most basic instincts and urges such as sex, hunger and aggression— may still carry some metaphorical or psychic meaning.
Reptililan brain or no, we do carry the history of evolution written in our DNA and in the structure of our bodies, but applying the word "aggression" to those primitive drives may be somewhat misleading. We usually think aggression has something to do with anger or hostility, but it's difficult to imagine that fish or reptiles take things personally, feel insulted and angry, and then behave aggressively. In fact, the Latin root of the word aggressive, which we can also see in words like egress or progress, is gradi: to step, to walk. So in this sense, aggression is something quite neutral: simply going forward.
Going forward is one of the most basic expressions of life. Of course, one may believe that everything in the universe is "alive" in some philosophical sense. But from the practical point of view, it doesn't seem that a rock feels hungry, and then takes action to fulfill its needs. A lion, on the other hand— or for that matter, even a bacterium— actively moves towards sources of food. In this sense, even bacteria behave "intentionally". They don't just sit there passively, letting the chaos of the environment take over. They make efforts to stay alive, going forward to seek what they need from their worlds. They embody a self-organizing principle, which is about as close as we have come to defining "life."
Symbolically, consciously moving forward through space suggests progress, stepping forward into a new world, leaving our old selves behind. Because they are a never-ending challenge, the jumping movements of Shintaido can re-introduce even the most athletic among us to the struggle to move forward, and by this they let us feel our connection with the primal foundations of all life. Fish gotta swim and birds gotta fly; bacteria wiggle, salmon swim upstream, and here and there on the surface of the earth in practice halls or on green fields, people dressed in white hop and jump.