Introduction: Muscle hypertrophy is one of the main outcomes from regular resistance training (RT) practice, but how it is modulated throughout training and the mechanisms regulating it are still obscure. It is known that intermittent increases in myofibrillar muscle protein synthesis (MPS) after RT bouts accumulate increasing muscle cross-sectional area (CSA). Indeed, studies have shown a qualitative agreement between MPS and hypertrophy, but, intriguingly we and others (1,2) recently reported that infusion-derived MPS, measured through hours after the first RT bout, did not align with the eventual hypertrophy after RT. Whether this have a physiological mechanistic reason as MPS was measured only after the first bout when, for example, muscle damage is highly pronounced burdening MPS to regenerate the tissue, or if it just a method issue (infusions trials, through hours only) of measuring MPS is not known. To explore this further, we used an integrated approach to measure MPS using deuterium-oxide and assessed muscle damage parameters, at the beginning (T1), 3wk into training (T2), and at 10wk of RT (T3). Methods: Ten young men (age: 27±1 y; BMI: 23.6±1.0 kg/m^2) were evaluated for muscle and fiber CSA by ultrasound at T1, T2 and T3 of RT. Integrated MPS analysis through D2O ingestion and muscle damage through Z-band streaming assessments were conducted before and 48h after the RT bout at T1, T2, and T3. Results: Hypertrophy only occurred significantly at T3. 48h integrated MPS increased after the RT bout at the 3 evaluation weeks, but the increase was greater at T1 than T2 and T3 (similar values at T2 and T3). Z-band streaming increased at T1, was mildly attenuated at T2 and strongly reduced at T3. Increases in MPS at both T2 and T3, but not at T1, were correlated (r~0.9, p<0.05) with hypertrophy. No significant correlations were found between muscle damage and hypertrophic responses. Discussion: Integrated MPS assessed at different phases of RT allowed a more precise and encompassing measurement to capture its contribution to chronic hypertrophy. At T1 muscle damage is the highest and MyoPS do not correlate with hypertrophy, and at T2 and T3 damage is progressively attenuated reaching a minimal magnitude, but MPS is highly correlated with hypertrophy. These facts added to the absence of any correlations between damage and MPS or hypertrophy precludes any role for muscle damage in hypertrophic responses.
© Copyright 2016 21st Annual Congress of the European College of Sport Science (ECSS), Vienna, 6. -9. July 2016. Veröffentlicht von University of Vienna. Alle Rechte vorbehalten.