Muscle hypertrophy is often discussed as a singular physiological event — a general increase in muscle size due to mechanical overload or anabolic stimuli. However, emerging insights from both basic science and applied physiology suggest this may be a misleading simplification.

Mechanistically, hypertrophy appears to manifest in at least two distinct forms:

• Adaptive hypertrophy: Characterized by increased protein synthesis, architectural remodeling, and translational efficiency — often occurring without overt cellular damage or inflammation.
• Regenerative hypertrophy: Triggered by structural muscle damage, especially in eccentric overload or injury models, requiring satellite cell (MuSC) activation and repair-based remodeling.

These two forms differ in:

• Signaling pathways (e.g., mTOR vs Notch/p38 MAPK)
• Cellular players (ribosomal biogenesis vs MuSC fusion)
• Time course and recovery requirements
• Functional outcomes (fiber integrity, ECM remodeling, etc.)

Despite this, most training studies and reviews treat hypertrophy as a monolithic outcome — potentially masking important mechanistic differences.

Should we, as a field, begin formally classifying hypertrophy as adaptive vs regenerative in both experimental design and interpretation?

Could this help clarify inconsistencies in training outcomes, satellite cell involvement, or age-related responses?

I'd love to hear from colleagues working in muscle physiology, regenerative biology, or sports science on this conceptual shift.