title: Resistance training-induced changes in integrated myofibrillar protein synthesis are related to hypertrophy only after attenuation of muscle damage.
abstract: Skeletal muscle hypertrophy is one of the main outcomes from resistance training (RT), but how it is modulated throughout training is still unknown. We show that changes in myofibrillar protein synthesis (MyoPS) after an initial resistance exercise (RE) bout in the first week of RT (T1) were greater than those seen post-RE at the third (T2) and tenth week (T3) of RT, with values being similar at T2 and T3. Muscle damage (Z-band streaming) was the highest during post-RE recovery at T1, lower at T2 and minimal at T3. When muscle damage was the highest, so was the integrated MyoPS (at T1), but neither were related to hypertrophy; however, integrated MyoPS at T2 and T3 were correlated with hypertrophy. We conclude that muscle hypertrophy is the result of accumulated intermittent increases in MyoPS mainly after a progressive attenuation of muscle damage.
  
  
  
  Skeletal muscle hypertrophy is one of the main outcomes of resistance training (RT), but how hypertrophy is modulated and the mechanisms regulating it are still unknown. To investigate how muscle hypertrophy is modulated through RT, we measured day-to-day integrated myofibrillar protein synthesis (MyoPS) using deuterium oxide and assessed muscle damage at the beginning (T1), at 3 weeks (T2) and at 10 weeks of RT (T3). Ten young men (27 (1) years, mean (SEM)) had muscle biopsies (vastus lateralis) taken to measure integrated MyoPS and muscle damage (Z-band streaming and indirect parameters) before, and 24 h and 48 h post resistance exercise (post-RE) at T1, T2 and T3. Fibre cross-sectional area (fCSA) was evaluated using biopsies at T1, T2 and T3. Increases in fCSA were observed only at T3 (P = 0.017). Changes in MyoPS post-RE at T1, T2 and T3 were greater at T1 (P < 0.03) than at T2 and T3 (similar values between T2 and T3). Muscle damage was the highest during post-RE recovery at T1, attenuated at T2 and further attenuated at T3. The change in MyoPS post-RE at both T2 and T3, but not at T1, was strongly correlated (r ≈ 0.9, P < 0.04) with muscle hypertrophy. Initial MyoPS response post-RE in an RT programme is not directed to support muscle hypertrophy, coinciding with the greatest muscle damage. However, integrated MyoPS is quickly 'refined' by 3 weeks of RT, and is related to muscle hypertrophy. We conclude that muscle hypertrophy is the result of accumulated intermittent changes in MyoPS post-RE in RT, which coincides with progressive attenuation of muscle damage.
authors.affiliation: School of Physical Education and Sport, University of São Paulo, Av. Prof. Mello de Morais, 65, 05508-030, São Paulo, SP, Brazil.
authors.forename: Felipe
authors.initials: F
authors.lastname: Damas
authors.affiliation: Department of Kinesiology, McMaster University, 1280 Main Street West, Hamilton, ON, Canada, L8S 4K1. phillis@mcmaster.ca.
authors.forename: Stuart M
authors.initials: SM
authors.lastname: Phillips
authors.affiliation: Department of Physical Education, Federal University of São Carlos, Rod Washington Luiz, km 235 - SP310, 13565-905, São Carlos, SP, Brazil.
authors.forename: Cleiton A
authors.initials: CA
authors.lastname: Libardi
authors.affiliation: School of Physical Education and Sport, University of São Paulo, Av. Prof. Mello de Morais, 65, 05508-030, São Paulo, SP, Brazil.
authors.forename: Felipe C
authors.initials: FC
authors.lastname: Vechin
authors.affiliation: School of Physical Education and Sport, University of São Paulo, Av. Prof. Mello de Morais, 65, 05508-030, São Paulo, SP, Brazil.
authors.forename: Manoel E
authors.initials: ME
authors.lastname: Lixandrão
authors.affiliation: School of Physical Education and Sport, University of São Paulo, Av. Prof. Mello de Morais, 65, 05508-030, São Paulo, SP, Brazil.
authors.forename: Paulo R
authors.initials: PR
authors.lastname: Jannig
authors.affiliation: School of Physical Education and Sport, University of São Paulo, Av. Prof. Mello de Morais, 65, 05508-030, São Paulo, SP, Brazil.
authors.forename: Luiz A R
authors.initials: LA
authors.lastname: Costa
authors.affiliation: School of Physical Education and Sport, University of São Paulo, Av. Prof. Mello de Morais, 65, 05508-030, São Paulo, SP, Brazil.
authors.forename: Aline V
authors.initials: AV
authors.lastname: Bacurau
authors.affiliation: Department of Kinesiology, McMaster University, 1280 Main Street West, Hamilton, ON, Canada, L8S 4K1.
authors.forename: Tim
authors.initials: T
authors.lastname: Snijders
authors.affiliation: Department of Kinesiology, McMaster University, 1280 Main Street West, Hamilton, ON, Canada, L8S 4K1.
authors.forename: Gianni
authors.initials: G
authors.lastname: Parise
authors.affiliation: School of Physical Education and Sport, University of São Paulo, Av. Prof. Mello de Morais, 65, 05508-030, São Paulo, SP, Brazil.
authors.forename: Valmor
authors.initials: V
authors.lastname: Tricoli
authors.affiliation: School of Physical Education and Sport, University of São Paulo, Av. Prof. Mello de Morais, 65, 05508-030, São Paulo, SP, Brazil.
authors.forename: Hamilton
authors.initials: H
authors.lastname: Roschel
authors.affiliation: School of Physical Education and Sport, University of São Paulo, Av. Prof. Mello de Morais, 65, 05508-030, São Paulo, SP, Brazil.
authors.forename: Carlos
authors.initials: C
authors.lastname: Ugrinowitsch
mesh_terms: D000328:Adult; D006801:Humans; D006984:Hypertrophy / Q000378:metabolism* / Q000503:physiopathology; D008297:Male; D009124:Muscle Proteins / Q000096:biosynthesis*; D009135:Muscular Diseases / Q000378:metabolism* / Q000503:physiopathology; D009210:Myofibrils / Q000378:metabolism*; D014176:Protein Biosynthesis; D055070:Resistance Training
chemical_list: D009124:Muscle Proteins