Resistance and endurance training differentially affect myofibrillar and mitochondrial protein synthesis at rest and following exercise in human skeletal muscle

We aimed to determine the acute and chronic changes in myofibrillar (MYOFIB) and mitochondrial protein synthesis rates (MITO) with aerobic exercise (AE) and resistance exercise (RE). We infused d 3 ‐α‐KIC at REST and for 4 hours after an acute bout of RE or AE prior to (UT) and following 10 weeks (TR) of training in healthy 20 yr old men. In the UT state, both MYOFIB (REST: 0.06±0.01, RE: 0.10±0.01 %/h, p=0.01) and MITO (REST: 0.08±0.02, RE: 0.14±0.04 %/h, p=0.02) increased following RE. Following TR only MYOFIB increased with RE (REST: 0.08±0.01, RE: 0.11±0.01 %/h, p=0.05), while MITO did not change from resting values (p=0.43). AE stimulated MITO (UT REST: 0.07±0.02, AE: 0.18±0.03, TR REST 0.07±0.01, AE: 0.15±0.03 %/h, p<0.05) but not MYOFIB regardless of training. In conclusion, RE acutely increases both MYOFIB and MITO, while AE increases MITO only. Acute responses to RE appear to be redundant in that synthesis of both MYOFIB and MITO were both stimulated. Following TR, the rate of MYOFIB was increased at rest with RE, and also following an acute bout of RE. By contrast AE activated only MITO in both the UT and TR states. These protein fraction responses are exercise specific and indicate the responses of mixed muscle protein synthesis are likely heavily influenced by exercise mode and training status. Supported by NSERC, CIHR, UK BBSRC, NIH‐NCRR.