The whole-body Tai Chi ball（全身太極球）
In Tai Chi, the whole body is understood as one integrated sphere—the whole-body Tai Chi ball（全身太極球）. Its center is the dantian（丹田）, located in the lower abdomen. The ball may expand or contract, becoming large or small, while trained power begins from its center and spreads throughout the body.
This traditional theory can be understood through ancient Tai Chi principles（古代太極理論）, physiology（生理學）, biomechanics（生物力學）, and energy transfer（能量傳遞）.
1. Ancient Tai Chi theory（古代太極理論）
The Tai Chi classics describe the body as a unified system:
“When one part moves, every part moves.”（一動無有不動）
This means that the hands should not move independently. The feet, legs, waist, spine, shoulders, and arms must participate in one coordinated action—whole-body integration（周身一體）.
The ball can become larger through opening and expanding（開／放）, or smaller through closing and gathering（合／收）. These are not merely arm movements. They are changes in the organization of the entire body.
Ancient theory also states:
“Power is rooted in the feet, generated by the legs, directed by the waist, and expressed through the fingers.”
其根在腳，發於腿，主宰於腰，形於手指。
Therefore, saying that power begins from the dantian does not mean that the abdomen alone produces force. It means that the dantian functions as the body’s central organizing point（中心統合點）, coordinating the force produced from the ground and transmitted through the whole body.
2. Physiological explanation（生理學解釋）
Physiologically, the dantian region corresponds approximately to the body’s lower trunk and pelvic core（下軀幹與骨盆核心）. This region includes:
The diaphragm（橫膈膜）
Deep abdominal muscles（深層腹肌）
Pelvic-floor muscles（骨盆底肌）
Multifidus muscles（多裂肌）
Hip and gluteal muscles（髖部與臀肌）
Muscles surrounding the lumbar spine（腰椎周圍肌群）
These muscles stabilize the trunk and help connect the upper and lower body. When breathing, posture, and movement are coordinated, they create intra-abdominal pressure（腹內壓）, which helps stabilize the spine without excessive stiffness.
Tai Chi breathing—abdominal breathing（腹式呼吸）—may also support relaxation, postural control, and awareness of internal movement. The nervous system coordinates many muscles in carefully timed sequences, known as neuromuscular coordination（神經肌肉協調）.
Thus, qi sinking to the dantian（氣沉丹田） may be interpreted practically as relaxing unnecessary tension, lowering the breath, stabilizing the trunk, and maintaining a calm, grounded posture.
3. Biomechanical explanation（生物力學解釋）
In biomechanics, the dantian is close to the body’s center of mass（身體重心）. It is also near the region where the pelvis, spine, and large muscles of the legs interact.
Effective Tai Chi movement often begins with a change in:
Ground pressure（地面壓力）
Weight distribution（重量分配）
Hip and waist rotation（腰胯旋轉）
Trunk orientation（軀幹方向）
Center-of-mass movement（重心移動）
When the feet press against the ground, the ground provides an equal and opposite ground-reaction force（地面反作用力）. This force travels through the legs, kua, pelvis, trunk, shoulders, arms, and hands. This connected route is called the kinetic chain（動力鏈）.
The Tai Chi ball represents this three-dimensional connection. The body can roll, rotate, rise, sink, expand, and contract around its center. A movement that appears circular at the hand is actually produced by coordinated rotations of several joints and body segments.
4. Energy and power（能量與力量）
In traditional language, qi（氣） and jin（勁） are related but not identical:
Qi（氣） refers to vitality, breathing, internal sensation, and the functional condition of the body.
Jin（勁） means trained, coordinated force.
Li（力） commonly means ordinary muscular strength.
From a scientific viewpoint, mechanical energy is produced by muscular activity and interaction with gravity and the ground. It is then transferred through the body’s connected structure. The dantian does not create mysterious energy; it organizes the body so that muscular force and ground-reaction force can be transmitted efficiently.
Tai Chi uses several related forms of energy:
Gravitational energy（重力能）
Elastic energy（彈性能）
Rotational energy（旋轉能量）
Momentum（動量）
Ground-reaction force（地面反作用力）
Relaxed muscles and connective tissues can temporarily store and release elastic energy（彈性能）, somewhat like a compressed spring. Rotation of the waist and hips produces torque（扭矩）, while coordinated opening and closing transfer energy through the limbs.
5. The ball can be large or small（球可大、可小）
When the Tai Chi ball becomes large, the practitioner expands awareness and structural connection through the arms, legs, and surrounding space. This is expansion or opening（開／放大）.
When the ball becomes small, the movement gathers toward the center while preserving structure. This is contraction or closing（合／縮小）.
Opening does not mean becoming stiff, and closing does not mean collapsing. Both require peng energy（掤勁）—a resilient, rounded, outward-supporting quality maintained in every direction.
The changing size of the ball also illustrates:
Yin and yang（陰陽）
Opening and closing（開合）
Rising and sinking（升降）
Gathering and releasing（蓄發）
Inward and outward movement（出入）
Opposition and extension（對拉拔長）
6. How force moves through the Tai Chi ball
The complete process can be described as:
Intention leads（意領） → breathing and core organize（氣息與核心統合） → the feet interact with the ground（足下作用於地面） → the legs and kua generate movement（腿胯發動） → the waist directs it（腰為主宰） → the spine and torso transmit it（脊柱與軀幹傳遞） → the hands express jin（勁達於手）.
Therefore, “power begins from the center of the ball”（運勁從球心起） means that every action is centrally organized. The dantian guides the timing and direction, while the actual force is produced and transmitted by the coordinated action of the ground, legs, pelvis, trunk, and limbs.
The essential idea is:
The entire body is a flexible Tai Chi ball（全身是一個靈活的太極球）. The dantian is its organizing center（丹田是統合中心）. The ball can expand or contract（球可大、可小）, and trained force travels from the center through the whole body（勁由中心貫通周身）. Ancient Tai Chi theory describes the principle, while physiology and biomechanics explain how the body performs it.
