Does habitual dietary intake influence myofiber hypertrophy in response to resistance training? A cluster analysis

Although resistance exercise training (RT) is a common intervention to stimulate muscle protein synthesis and increase skeletal muscle mass, the optimal daily protein and total energy intakes sufficient to support RT-mediated muscle growth are as yet unclear. Further, the efficacy of RT varies widely among adults of all ages and whether this is attributable to interindividual differences in nutrition is not known. To determine if self-selected daily intake of macronutrients and specific components of dietary protein and fat are predictive of the magnitude of RT-mediated muscle growth, detailed 4-day dietary records were analyzed on 60 subjects previously clustered (K-means cluster analysis) as non-, modest, and extreme responders (non, n = 16; mod, n = 29; xtr, n = 15), based on the magnitudes of change in vastus lateralis myofiber cross-sectional area following a 16-week, 3-day-per-week, high-intensity RT. Despite the marked contrast between 60% myofiber hypertrophy in xtr and zero growth in non, we found no differences among response clusters in daily intakes of energy (mean +/- SEM: non 102 +/- 8; mod 111 +/- 6; xtr 109 +/- 5 kJ.kg(-1).day(-1)), protein (non 0.97 +/- 0.08; mod 1.07 +/- 0.07; xtr 1.05 +/- 0.06 g.kg(-1).day(-1)), carbohydrate (non 3.02 +/- 0.24; mod 3.18 +/- 0.20; xtr 3.14 +/- 0.17 g.kg(-1).day(-1)), and fat (non 0.95 +/- 0.09; mod 1.05 +/- 0.08; xtr 1.03 +/- 0.08 g.kg(-1).day(-1)), which generally met or exceeded dietary recommendations. There were no cluster differences in intakes of branched chain amino acids known to stimulate muscle protein synthesis. Using the novel K-means clustering approach, we conclude from this preliminary study that protein and energy intakes were sufficient to facilitate modest and extreme muscle growth during RT and intrinsic or extrinsic factors other than nutrient ingestion apparently impaired the anabolic response in nonresponders.