Resistance exercise (RE) increases collagen synthesis in young and older men, whereas 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 yr; height: 1.78 ± 0.02 m; mass: 90 ± 4 kg) took part in this double-blind, crossover design study and undertook 4 × 10 repetitions of lower-limb RE at maximum load, after consuming 0 g, 15 g, or 30 g 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 30 g (169 ± 28 µg/mL × h) than 15 g (134 ± 23 µg/mL × h, P < 0.05) HC ingestion, and both 15 g and 30 g were higher than 0 g HC (96 ± 23 µg/mL × h, P < 0.05). RE with 0 g 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 30 g than 15 g and 0 g HC ingestion (P < 0.05) and greater with 15 g than 0 g 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 15 g HC rescues the collagen synthesis response and 30 g augments that response further. This dose response is associated with the increased bioavailability of collagen amino acids in the blood, which stimulate collagen synthesis.NEW & NOTEWORTHY This study is the first to document the dose-response effect of hydrolyzed collagen (HC) ingestion before resistance exercise (RE) on collagen turnover in middle-aged, resistance-trained men. Strikingly, RE alone did not increase collagen synthesis (suggesting connective tissue anabolic resistance), but ingesting 15 g HC rescued the collagen synthesis response and 30 g augmented that response further. These results were associated with the increased bioavailability of collagen amino acids in the blood, which stimulate collagen synthesis.
Keywords: connective tissue; glycine; hydroxyproline; proline; strength training.