Resistance exercise (RE) increases collagen synthesis in young and older men, while hydrolyzed collagen (HC) ingestion improves this response to RE in a dose-response manner in young men. However, the collagen synthesis response to RE with and without HC in middle-aged men is unknown. Eight resistance-trained men (age: 49±8 years; height: 1.78±0.02m; mass: 90±4kg) took part in this double-blind, crossover design study, and undertook 4×10 repetitions of lower-limb RE at maximum load, after consuming 0g, 15g, or 30g vitamin C-enriched HC. We analyzed venous blood samples for N-terminal propeptide of type 1 pro-collagen (PINP), β-isomerized C-terminal telopeptide of type 1 collagen (β-CTx) and 18 collagen amino acids throughout all three interventions. The serum PINP concentration×time area-under-the-curve (AUC) was higher following 30g (169±28 µg/mL×h) than 15g (134±23 µg/mL×h, P<0.05) HC ingestion, and both 15g and 30g were higher than 0g HC (96±23 µg/mL×h, P<0.05). RE with 0g HC showed no change in serum PINP concentration. The AUCs for glycine, proline, hydroxyproline, alanine, arginine, lysine, serine, leucine, valine and isoleucine were greater with 30g than 15g and 0g HC ingestion (P<0.05), and greater with 15g than 0g HC ingestion (P<0.05). Plasma β-CTx concentration decreased after RE independently of HC dose. Our study suggests connective tissue anabolic resistance to RE in middle-aged men but ingesting 15g HC rescues the collagen synthesis response, and 30g augments that response further. This dose-response is associated with the increased bioavailability of collagen amino acids in the blood, which stimulate collagen synthesis.
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