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J Appl Physiol (1985). 2019 Jul 3. doi: 10.1152/japplphysiol.00350.2019. [Epub ahead of print]

Myofibrillar protein synthesis and muscle hypertrophy individualised responses to systematically changing resistance training variables in trained young men.

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Department of Physical Education, Federal University of São Carlos, Brazil.
Department of Kinesiology, McMaster University, Canada.
Centre for Human and Applied Physiological Sciences, King's College London, United Kingdom.
School of Physical Education and Sport, University of São Paulo, Brazil.


The manipulation of resistance training (RT) variables is used among athletes, recreational exercisers and compromised populations (e.g., elderly) attempting to potentiate muscle hypertrophy. However, it is unknown whether an individual's inherent predisposition dictates the RT-induced muscle hypertrophic response. Twenty resistance-trained young (26(3)y) men performed 8wk unilateral RT (2∙wk-1) with one leg randomly assigned to a standard progressive RT (CON), and the contralateral leg to a variable RT (VAR, modulating exercise load, volume, contraction type and interset rest interval). The VAR leg completed all 4 RT variations every 2wk. Bilateral vastus lateralis cross-sectional area (CSA) was measured pre- and post-RT, and acute integrated myofibrillar protein synthesis (MyoPS) rates were assessed at rest and over 48h following the final RT session. Muscle CSA increase was similar between CON and VAR (P>0.05), despite higher total training volume (TTV) in VAR (P<0.05). The 0-48h integrated MyoPS increase post-exercise was slightly greater for VAR than CON (P<0.05). All participants were considered 'responders' to RT, although none benefited to a greater extent from a specific protocol. Between-subjects variability (MyoPS, 3.30%; CSA, 37.8%) was 40-fold greater than the intra-subject (between legs) variability (MyoPS, 0.08%; CSA, 0.9%). The higher TTV and greater MyoPS response in VAR did not translate to a greater muscle hypertrophic response. Manipulating common RT variables elicited similar muscle hypertrophy than a standard progressive-RT program in trained young men. Intrinsic individual factors are key determinants of the MyoPS and change in muscle CSA compared with extrinsic manipulation of common RT variables.


biological predisposition; individual responses; muscle protein synthesis; resistance exercise; training protocol

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