The Science of Posture and Movement Series — Examining the Relationship Between Gravity and the Body | Part 5
Introduction
“I keep up with both yoga and Pilates, yet my stiff shoulders and lower-back pain never get any better.”
It is a remark heard often in sessions. The superficial muscles are loosened, yet something deeper does not change — and the reason is that the approach is reaching a different “layer.”
What supports posture is not “muscle strength” but “the body’s response to gravity.” The concept that gave this question a scientific answer is “Tonic Function,” proposed by Hubert Godard, the French Rolfer and neuroscientist.
Tonic Function and Phasic Function — Two Ways the Body Works
Under the conditions of gravity, muscles operate in two ways.
Phasic Function — muscles that work “transiently” — handle conscious movements such as lifting an object or sprinting. They draw on glucose for energy and are governed by the alpha motor nervous system; in other words, they are muscles the brain can control directly. They are concentrated in the superficial layers, tire easily, and contract under stress and tension as well. Much stiff-shoulder and lower-back pain is the state in which these muscles have taken on the work of “maintaining posture,” a job that is not properly theirs.
Tonic Function — muscles that work “continuously” — are the deep muscles that hold posture around the clock, unconsciously. They draw on oxygen for energy and are governed by the gamma motor nervous system; rather than conscious will, they are handled by the unconscious, habitual nervous systems of the cerebellum and the medulla oblongata. They resist fatigue and engage automatically the moment gravity is detected.
The key to this automatic action is the muscle spindle. Deep muscles are rich in spindles, which sense the stretching and shortening of the muscle. When the body detects gravity, the spindle switches on, and the tonic muscles begin to work naturally without any conscious effort.
| Phasic (transient) | Tonic (continuous) | |
|---|---|---|
| Nervous system | Alpha motor system | Gamma motor system |
| Control | Conscious / voluntary | Unconscious / automatic |
| Location | Superficial | Deep |
| Fatigue | Tires easily | Resists fatigue |
| Energy source | Glucose | Oxygen |
When yoga or Pilates is slow to produce results, it is often because the superficial layer (Phasic) has not been released, so the spindles of the deep layer (Tonic) never switch on. Releasing the superficial layer first is the order of operations for restoring Tonic Function.
→ 重力と姿勢〜重力下で働く「一時的」「持続的」に働く筋肉を知る
Tonus (Muscle Tone) — A Sustained State of Readiness
The physiological basis of Tonic Function is “Tonus” (muscle tone).
Tonus means “keeping the tone of the muscle” — the sustained state of readiness that exists before a muscle moves. Where the alpha motor nerves issue the command “move,” the gamma motor nerves issue the command “stay ready to move at any moment.”
The quality of this muscle tone determines the quality of posture. What Rolfing aims for is to activate the gamma motor nervous system appropriately, so that the tonic muscles can reclaim their proper work — a natural response to gravity.
→ Tonic Function②：Tonusと2方向性の詳細
Why Trying to “Improve Posture” Backfires
“Straighten your spine,” “pull your shoulders back,” “tighten your core” — these are all commands to the Phasic system (conscious, quick to tire).
They attempt to substitute the Phasic system for a domain that the Tonic system (unconscious, sustained) is meant to handle. It is only natural that holding posture by conscious effort is tiring, because it asks the wrong muscles to do the wrong job.
There is a phrase, “let go of tension.” But it means nothing without knowing which muscle’s tension to release. The answer is to undo the over-tension of the phasic muscles. Releasing the state in which the Phasic system substitutes for the Tonic system’s job, so that the tonic muscles can reclaim their proper work — this is the essence of “letting go of tension.”
The Four Perspectives of Tonic Function
What Hubert Godard demonstrated is that Tonic Function is not simply a “muscle problem.” The body’s posture and tone are influenced from four perspectives.
① Coordination — How the body’s parts coordinate their movement determines the quality of Tonic Function. Habits and quirks of movement become engraved as patterns of muscular tension.
② Perception — How space, gravity, and environment are perceived directly alters the tonic state. The sense of peripersonal space (the personal space surrounding oneself) is directly linked to posture. This is precisely why Rolfing emphasizes not only “a direct approach to the fascia” but also a change in perception — how the body is felt within space.
③ Meaning — The meaning assigned to a situation affects the body’s tonic state. The meanings “this place is safe” or “there is a threat” change the body’s patterns of tension. It is a perspective that overlaps deeply with the trauma and attachment theory covered in the Somatic Psychology series.
④ Structure (Rolfing’s distinctive focus) — Working on the very structure of the body — its relationship with fascia, posture, and gravity — ripples out to all three perspectives above. When the body’s center comes into order, Coordination, Perception, and Meaning all change.
| Perspective | Content |
|---|---|
| Coordination | Patterns and habits of movement |
| Perception | How space and gravity are sensed |
| Meaning | Interpretation of, and emotion toward, a situation |
| Structure | Aligning the body’s center ← Rolfing’s distinctive focus |
Rolfing is said to “integrate the body” rather than “correct posture” because a direct approach to structure ripples out to all four of these.
Gravity and the Tonic Muscles — The Mechanism That Keeps the Body Balanced
There is a perspective deepened through a workshop with Gael Rosewood, a Rolf Movement trainer.
Gravity acts on the body at all times, and the tonic muscles make ceaseless, minute adjustments against it, continually supporting the body so that it does not fall. This process is not a conscious effort but an automatic dialogue between the nervous system and the muscles.
Trouble arises when the tonic muscles fall into over-tension, under-tension, or a mistaken pattern of activation. Much chronic shoulder stiffness, lower-back pain, and neck tension can be understood as a dysfunction of the tonic muscles. Rather than “kneading what feels tight,” what is needed is to ask anew, from the perspective of Tonic Function, “why was this pattern formed?”
→ 重力に関わるTonic Muscleが身体のバランスをどう保つのか
Movement and Tonic Function — A Rolf Movement Perspective
Tonic Function is directly linked not only to “static posture” but also to “the quality of movement.”
When Tonic Function works properly, the body can produce maximum efficiency with minimum force. An athlete’s “smooth movement” or a martial artist’s “relaxed power” is born not from the muscular strength of the Phasic system but from the natural response of the Tonic system. Conversely, when Tonic Function is disrupted, excess tension arises within movement, and the burden concentrates on particular regions of the body.
→ 身体の動きとTonic Functionをどう関連づけるか
To Study Tonic Function More Deeply
- 重力と姿勢〜重力下で働く「一時的」「持続的」に働く筋肉を知る
- Tonic Function①：ロルフィングの科学的理論の基礎
- Tonic Function②：Tonusと2方向性
- Tonic Function③：Space（空間認識との関係）
- 重力に関わるTonic Muscleが身体のバランスをどう保つのか
- 身体の動きとTonic Functionをどう関連づけるか
The Science of Posture and Movement Series — Examining the Relationship Between Gravity and the Body (6 parts)
Part 1: What Is the Difference Between Squatting and Sitting? — How Chair Culture Has Shaped the Body
Part 2: Why Is Sitting for Long Periods Bad for the Body? — The Science of Visceral Fat, Chronic Inflammation, and Stress
Part 3: Why Is “Standing” Not Tiring? — The Mechanism of Gravity and the Antigravity Muscles
Part 4: Why Is “Walking” Fundamental to Being Human? — The Science of Bipedal Locomotion, Center-of-Gravity Shift, and Gravity
Part 5: Why Good Posture Is Not a Matter of Muscle Strength — Tonic Function and Its Relationship to Gravity
Part 6: Why Does an “Easy Posture” Exist? — From the Perspective of Gravity, Fascia, and Rolfing
第1回：しゃがむと座るは何が違うのか──椅子文化が身体に与えた影響
→ 第1回を読む
第2回：なぜ長時間座ると身体に悪いのか──内臓脂肪・慢性炎症・ストレスの科学
→ 第2回を読む
第3回：なぜ「立つ」は疲れないのか──重力と抗重力筋の仕組み
→ 第3回を読む
第4回：なぜ「歩く」は人間の基本なのか──二足歩行・重心移動・重力の科学
→ 第4回を読む
第5回：なぜ「姿勢の良さ」は筋力ではないのか──Tonic Functionと重力の関係（この記事）
第6回：なぜ「楽な姿勢」は存在するのか──重力・筋膜・ロルフィングの視点から
→ 第6回を読む
Understanding posture and movement scientifically is one entry point for updating the “Recognition OS.” The theme of integrating thought, emotion, and body is explored in greater depth in the “Recognition OS” series at Mind and Bodywork Lab.
→ Mind and Bodywork Lab: How to Navigate This Site (only in Japanese)
A trial session is a place to begin by confirming what is happening within the body.
Hidefumi Otsuka, Ph.D. | Certified Advanced Rolfer™ / Rolf Movement Practitioner
Completed the doctoral program at the University of Tokyo Graduate School of Medicine. After a career in the pharmaceutical industry, has offered Rolfing® sessions in Shibuya since 2015, working under the theme of “the integration of thought, emotion, and body.”