Resistance training reduces muscle protein turnover

Resistance training results in muscle hypertrophy, requiring a stimulation of muscle protein turnover such that muscle protein synthesis exceeds breakdown. We examined the hypothesis that resistance training would attenuate the acute increase in muscle protein turnover seen following exercise. Muscle protein turnover was determined in persons (N=6) who regularly performed resistance exercise (trained - T; 74.8±5.0kg; means±SE) and controls (N=6: untrained - UT: 70.4±8.4kg). Exercise was 80 repetitions of single leg. eccentric, knee flexion (at 120% of the subject's single repetition maximum). The contralateral inactive leg served as a non-exercised control. Fractional synthetic rate (FSR) and fractional breakdown rate (FBR) of mixed muscle proteins were determined using primed continuous infusions of [²H5]phenylalanine and [¹⁵N]phenylalanine, respectively. Exercise resulted in an increase in FSR, greater than the resting leg, of 49±6% in T and 119±18% in UT (P<0.05). Mixed muscle protein FBR also increased 16±3% in T and 37±6% in UT (P<0.05). The result was an increase (P<0.05) in muscle net balance (FSR - FBR) in both the T (34±11%) and UT (38±5%; P>0.05). In addition, there was a significant correlation between FSR and FBR (r = 0.83; P<0.01). These results show that resistance exercise acutely increases muscle protein balance. However, resistance training results in a blunting of the response of muscle protein turnover, in response to exercise. In addition, the correlation between FSR and FBR suggests that one process may be affecting the other, potentially by a demand for amino acids.