PURPOSE: In response to aerobic training some individuals exhibit significant improvement inone or more training variables (high responders), whereas some others experience few to no changes or even display an adverse adaptation in the same training variables (low responders This study using a contrasting animal model where rats have been artificially selected for high and low response to running exercise aims to reveal the differences in capillarity, fibre type distribution and fibre size in EDL (extensor digitorum longus) muscle between 1) high and low responder rats in sedentary state 2) sedentary and endurance trained rats within both low an high response selection lines.
METHODS AND MATERIALS: After two-way artificial selective breeding of rats for low and hig response to running exercise, rats from generation 22 were studied in trained and sedentary state. Immunohistochemistry was performed to identify MHC (myosin heavy chain) phenotyp laminin and capillaries in EDL muscle. Two sample t-tests were used for the statistical analysis.
RESULTS: The fibre type proportion and fibre size did not differ between high and low responders or between sedentary and endurance trained rats. However, high responders had significantly higher capillary supply than low responders. Finally, both high and low responder trained rats experienced impaired exercise-induced angiogenesis.
CONCLUSION: We demonstrate that even in sedentary state, rats with high adaptational capacity for running exercise display a more enriched capillary network compared to rats that cannot improve notably their running performance in response to endurance training.Furthermore, blunted exercise-induced angiogenesis seen in rats from both selection lines recommends that the peripheral component can be a limiting factor of aerobic performance even in rats with high adaptability to endurance training.