Resistance training results in selective hypertrophy of skeletal muscle in both young and middle‐age rats

Resistance training results in significant increase in muscle mass of flexor hallucis longus (FHL) in both young and middle‐age rats. Purpose : Study if there is a difference between young and middle‐age rats in responsiveness to eight weeks of resistance training. Methods : Twenty female Sprague‐Dawley rats, 2 (Young) or 15 months (Middle‐age) of age (each n=10), underwent resistance training for 3d/wk for 8 wks by climbing an 85°, 1m high ladder with weights attached to their tails. There were sedentary controls. Results : After 8 wks of training, 24% and 23% increasein muscle mass were observed in the FHL, the major muscle recruited in climbing activity, of Young and Middle‐age groups. The rats in both groups pulled over 3 times of their body weight up the ladder during their last training sessions. There was no significant increase in muscle mass in soleus and plantaris showing selective hypertrophy for FHL. The citrate synthase activity and muscle fiber type distribution were not significant different from their sedentary controls. Conclusion : 8 wks of resistance training results in selective hypertrophy of FHL in rat skeletal muscle. There was no significant difference in responsiveness to resistance training between young and middle‐age rats. These findings suggest that aged rats still have the capacity to adapt in response to resistance type exercise. Supported by Korea Research Foundation 2005‐013‐G00024