Muscle fiber splitting in stretch-enlarged avian muscle

Area of Science:

• Muscle physiology
• Skeletal muscle adaptation
• Animal models in research

Background:

• Muscle hypertrophy is a complex adaptation process.
• Understanding the mechanisms of muscle growth, such as fiber splitting, is crucial.
• Previous research has explored stretch overload, but specific mechanisms in ALD muscle require further investigation.

Purpose of the Study:

• To investigate the role of longitudinal fiber splitting in the anterior latissimus dorsi (ALD) muscle of adult quail.
• To determine if progressive stretch overload (PSO) influences fiber number through splitting.
• To compare the effects of PSO with chronic stretch overload.

Main Methods:

• Induction of muscle hypertrophy via a progressive stretch overload (PSO) model in quail.
• Measurement of muscle mass and length after 16 and 28 days of PSO.
• Assessment of fiber number using direct counts after nitric acid digestion.
• Quantification of longitudinal fiber splitting frequency.

Main Results:

• Significant increases in ALD muscle mass (188% at 16d, 294% at 28d) and length (approx. 77%) were observed under PSO.
• Fiber number did not change at 16 days but increased by 30% at 28 days of PSO.
• Longitudinal fiber splitting was minimal (<0.3%) except in the 28-day PSO group, where 5.25% of fibers showed splitting.

Conclusions:

• Progressive stretch overload (PSO) significantly enhances ALD muscle mass and length in quail.
• Longitudinal fiber splitting emerges as a significant contributor to the increase in fiber number after prolonged PSO.
• The mechanism of muscle growth induced by PSO differs from that of chronic stretch overload, highlighting the importance of splitting.