What is the Origin of Myofibrillar Accretion?

This term is a precise descriptor used in exercise physiology and muscle biology, combining the Greek roots myo- (muscle) and fibril (small fiber) with the Latin accretio (growth). It specifically defines the growth of the contractile elements, distinguishing it from sarcoplasmic hypertrophy.

What is the Mechanism of Myofibrillar Accretion?

Myofibrillar Accretion is initiated when mechanical stress from resistance exercise causes microtrauma to the muscle fibers, activating satellite cells and initiating intracellular signaling cascades, notably the Akt/mTOR pathway. Activation of mTOR enhances the translational machinery, increasing the rate of protein synthesis and decreasing the rate of protein breakdown. This leads to the net deposition of new actin and myosin filaments, which are integrated into the existing myofibrils, structurally reinforcing the muscle fiber and increasing its force-generating capacity.

Myofibrillar Accretion ∞ Area

Myofibrillar Accretion

Meaning

The cellular process of increasing the quantity and density of myofibrils, the contractile protein filaments (actin and myosin) within muscle fibers, leading directly to an increase in muscle fiber size and, consequently, muscular strength and hypertrophy. This anabolic event is the structural basis for functional strength gains and is tightly regulated by mechanical tension, nutrient availability, and the systemic signaling of anabolic hormones. It is a key physiological outcome of effective resistance training protocols.