Collagen Supplementation on Tendon-Related Structural and Performance Outcomes: A Systematic Review

Background: Tendons adapt to mechanical loading by increasing cross-sectional area (CSA), stiffness, and matrix organization, with structural remodeling critical for both rehabilitation and performance. Collagen supplementation has been proposed to enhance this process by supplying key amino acids for collagen synthesis. However, inconsistent results across trials have limited its clinical and athletic application. Methods: A comprehensive search of PubMed, EMBASE, CINAHL, and Web of Science was conducted in May 2025. The risk of bias was assessed using the PEDro scale; studies scoring ≥6/10 were classified as good-to-excellent quality. Data extraction included collagen type, dose, training modality, intervention duration, and outcome measures. Results: Of 887 unique citations, 8 RCTs (n = 257; ages 18–52; 246 M:11 F) met inclusion criteria. All studies included resistance or plyometric training for 3–15 weeks. Three of four studies reported significantly greater increases in tendon CSA in collagen groups versus placebo. Four studies investigated tendon stiffness and Young’s modulus; the two using higher doses (15–30 g/day) demonstrated significant between-group improvements favoring collagen, while two lower-dose studies (~5 g) showed only within-group effects. Muscle strength improved with training in all trials, but no additive effects of collagen were observed. One study reported improvements in eccentric rate of force development and deceleration impulse with collagen, though gross explosive metrics (e.g., jump height) remained unaffected. Conclusion: Collagen supplementation (15–30g) with vitamin C (≥ 50mg) may enhance tendon remodeling when combined with high-intensity resistance training (≥70% 1RM). The current literature indicates a GRADE A recommendation (strong evidence) for increases in tendon cross-sectional area and tendon stiffness, GRADE A (strong evidence) against an effect on muscle strength, and GRADE C (conflicting evidence) for muscle cross-sectional area and physical performance. Limitations of the literature include small sample sizes, heterogeneous protocols and short intervention durations. Future trials should standardize protocols, include diverse populations, and examine long-term adaptations to optimize clinical and performance outcomes.