Participants will consume 12 half-hourly (6 hours) isoenergetic, isonitrogenous beverages containing 0.9g/kg fat-free mass/day protein. Drinks will be enriched with stable isotopes [2H5]Phenylalanine and [1-13C]Phenylalanine, which will respectively allow for determination of muscle protein synthesis and whole-body protein synthesis over the subsequent 6 hours of feeding.

Participants will consume 12 half-hourly (6 hours) isoenergetic, isonitrogenous beverages containing 0.9g/kg fat-free mass/day protein. Drinks will be enriched with stable isotopes [2H5]Phenylalanine and [1-13C]Phenylalanine, which will respectively allow for determination of muscle protein synthesis and whole-body protein synthesis over the subsequent 6 hours of feeding

Rate of whole-body phenylalanine excretion following orally ingested amino acid tracer [1-13C]Phenylalanine determined from the product of breath 13CO2 enrichment and carbon dioxide production rate (VCO2).

Rate of whole-body phenylalanine oxidation following orally ingested amino acid tracer [1-13C]Phenylalanine determined from the correction of phenylalanine excretion by the phenylalanine precursor enrichment via urine enrichment.

Rate of myofibrillar fractional synthesis is determined by rate of incorporation of orally ingested tracer [2H5]Phenylalanine into myofibrillar proteins (isolated from skeletal muscle biopsies) and the enrichment of [2H5]Phenylalanine in plasma collected over the 6 hours protein consumption period. Enrichment will be quantified via tandem LC-MS/MS to derive a rate of incorporation over the 6-hour period.

Rate of sarcoplasmic fractional synthesis is determined by rate incorporation of orally ingested tracer [2H5]Phenylalanine into sarcoplasmic (ie., soluble) proteins (isolated from skeletal muscle biopsies) and the enrichment of [2H5]Phenylalanine in plasma collected over the 6 hours protein consumption period. Enrichment will be quantified via tandem LC-MS/MS to derive a rate of incorporation over the 6-hour period.