| Summary: | Background: The aim of this study was to investigate the effect of whey protein supplementation on myofibrillar protein synthesis (myoPS) and muscle recovery over a 7-d period of intensified resistance training (RT). Methods: In a double-blind randomised parallel group design, 16 resistance-trained men aged 18 to 35 years completed a 7-d RT protocol, consisting of three lower-body RT sessions on non-consecutive days. Participants consumed a controlled diet (146 kJ·kg<sup>−1</sup>·d<sup>−1</sup>, 1.7 g·kg<sup>−1</sup>·d<sup>−1</sup> protein) with either a whey protein supplement or an isonitrogenous control (0.33 g·kg<sup>−1</sup>·d<sup>−1</sup> protein). To measure myoPS, 400 ml of deuterium oxide (D<sub>2</sub>O) (70 atom %) was ingested the day prior to starting the study and m. vastus lateralis biopsies were taken before and after RT-intervention. Myofibrillar fractional synthetic rate (myoFSR) was calculated via deuterium labelling of myofibrillar-bound alanine, measured by gas chromatography-pyrolysis-isotope ratio mass spectrometry (GC-Pyr-IRMS). Muscle recovery parameters (i.e., countermovement jump height, isometric-squat force, muscle soreness and serum creatine kinase) were assessed daily. Results: MyoFSR PRE was 1.6 (0.2) %∙d<sup>−1</sup> (mean (SD)). Whey protein supplementation had no effect on myoFSR (<i>p</i> = 0.771) or any recovery parameter (<i>p</i> = 0.390−0.989). Conclusions: Over an intense 7-d RT protocol, 0.33 g·kg<sup>−1</sup>·d<sup>−1</sup> of supplemental whey protein does not enhance day-to-day measures of myoPS or postexercise recovery in resistance-trained men.
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