The Effects of Ingesting a Single Bolus of Hydrolyzed Collagen versus Free Amino Acids on Muscle Connective Protein Synthesis Rates

The suggested anabolic properties of hydrolyzed collagen on connective tissue may be attributed to the delivery of amino acids as precursors or to anabolic signaling properties of bioactive peptides. Purpose To assess the impact of ingesting a single bolus of hydrolyzed collagen or free amino acids on myofibrillar and muscle connective protein synthesis rates. Methods In a randomized, double-blind, parallel design, 45 young male (n = 21) and female (n = 24) adults (age: 23 ± 3 y; BMI: 22.3 ± 2.2 kg/m2) received intravenous infusions with L-[ring-13C6]-phenylalanine. Following unilateral resistance exercise, participants ingested either 30 g hydrolyzed collagen (COLL, n = 15), 30 g free amino acids reflecting the collagen amino acid profile (AA, n = 15), or a non-caloric placebo (PLA, n = 15). Blood and muscle tissue samples were collected over 6 h to assess myofibrillar and muscle connective protein synthesis rates and associated signaling responses. Results Both collagen and free amino acid ingestion substantially increased circulating plasma amino acids concentrations and effected collagen turnover proteins. Collagen and free amino acid ingestion did not significantly increase myofibrillar protein synthesis rates in the rested (0.039 ± 0.011, 0.037 ± 0.010, and 0.036 ± 0.015%·h-1 in PLA, COLL and AA, respectively) or the exercised (0.049 ± 0.010, 0.048 ± 0.011, and 0.045 ± 0.013%·h-1) leg (P > 0.05). Similarly, both collagen and free amino acid ingestion did not significantly increase muscle connective protein synthesis rates in the rested (0.065 ± 0.014, 0.063 ± 0.017, and 0.061 ± 0.025%·h-1 in PLA, COLL and AA, respectively) or the exercised (0.098 ± 0.023, 0.092 ± 0.028, and 0.085 ± 0.024%·h-1) leg (P > 0.05). Conclusions Ingestion of a single bolus of collagen hydrolysate or free amino acids substantially increases circulating amino acids concentrations, particularly glycine, but does not further increase myofibrillar or muscle connective protein synthesis rates at rest or during recovery from exercise in healthy, recreationally active young men and women.