“Window of anabolic opportunity” refers to the time period after exercise training when muscle protein synthesis is elevated. Which factors affect this anabolic response?
Exercise training or feeding? The general concept is that exercise is capable of turning on anabolic signaling and that feeding maximizes this effect. Indeed, studies show that resistance training induces an increase in muscle protein synthesis even in the absence of protein feeding. Protein intake and resistance training may increase muscle protein synthesis by about 15-25% compared with training alone (Phillips et al., 1997).
How long is anabolism sustained after exercise training? It seems that acute resistance exercise-induced muscle protein synthesis is sustained for 48h. The peak of muscle protein synthesis rate depends on training level. However the higher rate is observed at 4 hours post exercise in trained and around 16 hours in untrained individuals (Tang et al., 2008).
Does exercise intensity affect anabolic rate? Resistance exercise training at loads higher than 70% of maximal is required to stimulate muscle protein synthesis. In untrained subjects or untrained limbs, exercise intensities as low as 20-30% of maximum with working muscle blood flow occlusion may also stimulate muscle anabolism.
Does amino acid amount and type affect anabolism? Yes. It seems that essential amino acids (EAA) are necessary for the stimulation of muscle protein synthesis. The guidelines are for 20 g of intact dietary protein intake or 8-10 gr of EAA to maximize protein anabolism. Proteins that are digested at a fast rate such as whey or soy are the best choices.
Timing of amino acid ingestion: does it matter? Timing of ingestion is a major issue. Literature review suggests that an increase in amino acid availability in close time proximity with resistance training may be beneficial to muscle protein synthesis. More benefits are gained when amino acids are ingested either before or/and within 1 hour after resistance exercise.
For more reading
Phillips et al. Am J Physiol 273:E99-107, 1997
Tang et al. Am J Physiol 294:R172-178, 2008