[Purpose] The qi-transformation (气化) theory in Chinese medicine describes the rhythmic adjustment of human physiological functions across seasons, but its driving source has long remained unidentified. Modern chronobiology has confirmed the molecular mechanism of the human biological clock but has not "why rhythms necessarily exist." Starting from the planetary dynamics framework established in the author's previous work, this paper aims to derive the physical source of human rhythms and provide a dynamic definition for qi-transformation theory. [Method] Taking the planetary north-south oscillation mechanism established in the author's previous work "From Geothermal Anomaly to Layer Oscillation: Geodynamic Effects of Gravitational Torque from the Obliquity of the Ecliptic" as the starting point, and through the observable bio-planetary coupling phenomenon of animal migration and hibernation, this paper establishes a dynamic definition of "qi-transformation"—the phase synchronization process between life systems and the planetary rhythm base. On this basis, the dynamic isomorphism between the human dual-layer structure (ying-wei) and Earth's dual-layer circulation is derived, and a rhythm dynamics model of disease progression is constructed. [Results] 1. Animal migration and hibernation are extreme behavioral expressions of qi-transformation, demonstrating observable phase locking between life systems and the planetary rhythm base; 2. Human qi-transformation is the same mechanism expressed at the physiological level, with four-season pulse patterns as its clinically observable window; 3. Disease progression can be described as cumulative phase drift: health (phase synchronization) → functional imbalance (phase drift, reversible) → organic pathology (pathological rhythm formation, sustained antagonism with the terrestrial baseline); 4. The reason qi-transformation has been difficult for modern science to understand is that its driving source (planetary north-south oscillation) had not been previously identified. [Conclusion] Human rhythms are not "implanted" preset programs, but temporal structures that necessarily emerge as life systems—semi-open homeostatic systems—maintain their own existence. The planetary north-south oscillation establishes a unified annual energy temporal base for the Earth's surface; human qi-transformation is the compelled response to this base. Health is the state in which all system rhythms operate in coordination; disease is the manifestation of rhythm dissonance.