Firm and soft/fluid are complimentary not contradictory.
Firm to allow energy transfer.
Firmness allows energy transfer. In karate training—whether in adult karate classes, childrens karate classes, or even self defense classes for kids—we learn that being too rigid blocks the flow, while being too loose causes disconnection. The balance of firmness and fluidity lets energy transfer smoothly through the kinetic chain.
We are not only firm at kime but throughout the technique, even though the muscles activation is different at moving and at kime.
Aiko San and sensei Nishiyama constantly told me “keep the very inside (around the sacrum) strong and the outside soft and flexible.” Of course, to be able to apply and get the feel of this we need proper training methods and good feedback.
Sport research confirms this, for force transfer between the legs to torso to arms and vice versa (through the sacrum), the smaller, local muscles around the sacrum have to activate and stabilize the sacrum.
Connection and disassociation.
Sports research confirms this: for energy transfer between legs, torso, and arms (through the sacrum), smaller local muscles must stabilise the sacrum. This principle is vital in adult karate classes, where power generation depends on internal stability.
We must connect all segments of the body, but not over-tense. For example, to increase energy transfer from the sacrum to the thoracic spine, the thoracic spine must move slightly more than the sacrum and lumbar. This is disassociation. If we brace too much, the body moves as one piece and energy is blocked. If too loose, there is no connection, and power is lost.
In childrens karate classes or self defense classes for kids, these principles are introduced in simple, practical ways—teaching young students how to control their body while staying relaxed yet strong.
The Balance of Firmness and Relaxation
When someone braces too much at the shoulder or hip, energy cannot transfer smoothly. Disassociation allows subtle adjustments at the hip or shoulder, which are essential for smooth weight shifting, footwork, and force production.
Firmness also allows true relaxation. If the spine isn’t stabilised by smaller muscles, the bigger movement muscles become stiff and less efficient. But when the inner muscles activate correctly, the larger muscles can contract and expand to their full potential.
This balance—taught in both adult karate classes and youth training—is what enables efficient, powerful, and fluid motion.
The Bigger Picture
Our body is the most complex machine ever created. To achieve simplicity in movement, we must first understand the complexity. At the end, in sparring or competition, you don’t consciously think of firmness, softness, or disassociation—you simply act. Everything flows because you trained hard and correctly.
Whether it’s adult karate classes focused on precision, or self defense classes for kids and childrens karate classes building fundamentals, the principle remains the same: firm inside, fluid outside, always connected.