TLDR
In a study of 45 healthy young adults in the Netherlands, researchers compared the effects of collagen, its free amino acid equivalent, and a placebo on protein synthesis after exercise.
After participants performed one-leg resistance exercise and drank one of the test drinks, researchers measured muscle and skin protein synthesis, plasma amino acid and insulin levels, and collagen turnover markers over 6 hours using stable isotope tracers and biopsy analyses.
Key Findings
- Exercise alone, not collagen, increased muscle connective tissue and myofibrillar protein synthesis.
- Neither collagen nor free amino acid consumption further increased synthesis in muscle, connective tissue, or skin compared with placebo.
- Collagen turnover markers (P1NP, CTX-I) varied over time but showed no treatment effects.
- Men and women showed small differences in baseline and post-consumption synthesis rates, but these did not alter overall outcomes.
Bottom Line
Hydrolyzed collagen and its free amino acid mixture do not meaningfully boost muscle or connective tissue protein synthesis after resistance exercise in healthy adults, despite short-term increases in circulating amino acids and insulin. Exercise itself remains the dominant driver of muscle remodeling.
Purpose of the Study
To compare how hydrolyzed collagen and its constituent free amino acids affect muscle connective tissue protein synthesis after resistance exercise. They also evaluated how these supplements influence myofibrillar protein synthesis, resting and post-exercise connective tissue synthesis, skin protein synthesis, and plasma amino acid availability.
Methods:
The study took place in the Netherlands and included 45 healthy, non-obese young adults. Participants received intravenous infusions of L-[ring-^13C_6]-phenylalanine to trace protein synthesis. After a resistance exercise session, they consumed either 30 g of hydrolyzed collagen, 30 g of matched free amino acids, or a non-caloric placebo.
Each participant followed the same unilateral leg workout. Researchers randomized which leg to train. The workout included six sets on both the leg press and leg extension machines. Participants performed 6 sets of 8–10 reps: the first two at 55% and 65% 1RM, and sets 3–6 at 75% 1RM, resting 2 minutes between sets and exercises. The team assessed perceived exertion using the Borg scale.
Over the following 6 hours, researchers collected blood, muscle, and skin samples. They measured glucose and insulin with enzymatic assays and analyzed plasma amino acids using ultra-performance liquid chromatography–mass spectrometry (UPLC-MS). They obtained muscle biopsies from the vastus lateralis and skin biopsies from the buttock to measure myofibrillar and connective tissue protein synthesis.
The team also measured collagen formation (P1NP) and resorption (CTX-I) using chemiluminescent immunoassays. They calculated fractional synthetic rates (FSR) of muscle and skin proteins from isotopic tracer data relative to plasma enrichment levels.
Statistics
The researchers powered the study to detect a 20% difference in postprandial connective tissue protein synthesis between groups. They calculated that 14 participants per group would provide 80% power, adjusting the significance level to α = 0.0167 for multiple comparisons. To account for dropouts, they included 15 participants per group.
They checked data normality using the Shapiro–Wilk test and sphericity using Mauchly’s test, applying Greenhouse–Geisser corrections when necessary. They used one-way ANOVA to compare baseline characteristics and dietary intake. For time-dependent outcomes (e.g., plasma glucose, insulin, amino acids, tracer enrichments, and collagen turnover markers), they used mixed-model ANOVA.
They analyzed myofibrillar and connective tissue FSR using repeated-measures ANOVA with condition (basal, exercised, rested) as the within-subject factor and treatment as the between-subject factor. Secondary analyses explored early and late postprandial phases. One-way ANOVA assessed non–time-dependent variables such as skin FSR and iAUC. They applied Bonferroni corrections where appropriate and set significance at P < 0.05.
Results
Participant Characteristics and Dietary Intake
The three groups did not differ in baseline characteristics or dietary intake. All participants consumed sufficient vitamin C in the days before testing (≈150 mg/day)
Primary Outcome:
Muscle Connective Tissue Protein Synthesis
Collagen and amino acid supplementation did not increase connective tissue protein synthesis.
Post-absorptive synthesis rates were similar across all groups, and exercise clearly increased synthesis afterward. In other words, exercise, not collagen or amino acid supplementation, was responsible for the rise in connective tissue protein synthesis.
In early (0–180 min) and late (180–360 min) recovery phases, the exercised leg maintained higher synthesis rates than the rested leg, regardless of treatment.
Post hoc sex analysis revealed that women had higher baseline connective tissue synthesis, but men showed larger post-exercise increases .
Secondary Outcomes
Myofibrillar Protein Synthesis
Exercise increased muscle protein synthesis in both legs, and this effect was similar across all groups. The supplements did not provide any additional benefit compared with the placebo. A follow-up analysis confirmed higher synthesis in the exercised leg, regardless of supplementation. Women showed slightly higher baseline synthesis rates, while men experienced larger increases after exercise.
Skin Protein Synthesis
Skin protein synthesis was similar across all groups and did not differ between treatments. Overall, skin protein synthesis remained much lower than that of muscle or connective tissue.
Plasma Glucose, Insulin, and Amino Acids
Hydrolyzed collagen and amino acids temporarily increased blood glucose and insulin levels during the first two hours after ingestion. Both supplements also raised amino acid levels in the blood, particularly glycine, proline, and hydroxyproline. Collagen uniquely increased hydroxylysine, while the amino acid mixture caused slightly higher peaks of proline and hydroxyproline.
Isotope Tracer and Protein Signaling
Tracer levels varied slightly between groups early in recovery but were similar overall. The study found no major differences between groups in protein signaling. MMP-1 increased in the exercised leg for both the collagen and amino acid groups compared with the placebo, while MMP-8 was higher in the rested leg later in recovery, regardless of treatment.
Plasma Collagen Turnover Markers
P1NP levels changed over time but were similar across all groups. CTX-I levels varied during the recovery period but did not differ consistently between treatments. In both the collagen and amino acid groups, CTX-I temporarily dropped between one and three hours after ingestion and then returned to baseline or slightly higher by six hours
Notes and Limitations:
This was a rigorous, mechanistic study using gold-standard stable isotope tracer methods to quantify protein synthesis. However, the findings reflect acute molecular responses, not long-term adaptations in muscle or connective tissue structure. Future research should explore chronic supplementation and functional outcomes, especially in populations with impaired tissue repair.
The study was funded through a public–private partnership between Maastricht University and the Tessenderlo Group NV (Belgium). Several investigators, including Luc van Loon, Tim Snijders, Andrew Holwerda, and Keith Baar, have received research support or consulting fees from collagen-producing or nutrition-related companies (e.g., Gelita, Tessenderlo, PepsiCo). All authors declared transparent reporting, and no data manipulation or fabrication was noted. These relationships should be acknowledged when interpreting the findings.